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A Computer Darkroom Review

Although Photoshop CS (AKA Photoshop 8.0) contains many enhancements and new features we find that the overall appearance remains virtually unchanged from earlier versions.

 

Likewise the colour management system and settings will be familiar to those who previously used Photoshop 6 or 7. All of this is good news for those migrating from earlier versions but colour management and particularly the plethora of options associated with it can leave many new users in a state of confusion.

This essay is primarily intended to help new Photoshop users and will explain how the colour management system within Photoshop CS should be configured. That said and before getting into the specifics I think it worth taking a few moments reviewing the underlying principles of colour management.

Colour Management Primer

Ever since the beginning of colour reproduction, colour management has existed in one form or another. The basic concept underlying colour management is to ensure that colour data is processed in a consistent and predictable way throughout the entire imaging workflow. A typical Imaging System will consist a wide range of Input and Output Devices, and each device will reproduce colour differently. This means that a colour represented by one device will rarely if ever match the same colour represented on another device. In other words, colour is device-dependent. So expanding upon our earlier definition we can say that the purpose of a Colour Management System (CMS) is to maintain the consistent and accurate appearance of a colour on different devices (e.g. scanners, monitors, printers, etc.) throughout our imaging workflow.

Components of a Colour Management System

In order that we can achieve the above aims a colour managed system will require three basic components, namely: -

  • A device-independent colour space - this is usually referred to as the Working Space or Reference Colour Space.

  • ICC/ColorSync device profiles for each device (printer, scanner, monitor, digital camera, etc.) that describe the colour characteristics of the specific device.

  • A Colour Matching Module (CMM) that will interpret the information contained within a device profile and carry out the instructions on the way the colour gamut of each device should be treated.

The following diagram demonstrates a typical Colour Managed Workflow and shows the image being passed along the chain - from scanner/digital camera - to - computer - to - monitor - and printer with the ICC profiles ensuring that the colour data from/to each device is correctly described.

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Colour Numbers, their Meaning, and Profiles

A digital image will comprise pixels each of which is represented by a number. This number will describe the location of the pixel within the image and its particular colour value (typically an RGB value). We have already noted that since colour is device-dependent the appearance of the each coloured pixel will vary for each device. We also noted that this is because each device has its own unique way of translating the raw colour value into visual colour. To minimise the discrepancies that result from the widely differing colour characteristics of each device we use an ICC profile to inform the CMM how the colour values produced by that device should actually appear. This may be on our monitor, in print or on film output. In simple terms it is the device profile that conveys the meaning of the raw colour numbers associated with each pixel.

Whilst consumer class film and flatbed scanner software applications are now ICC/ColorSync aware they tend to be based upon a colour space known as sRGB, likewise consumer digital cameras. This colour space isnít generally regarded as appropriate for high quality image editing, especially when print or film output is required, but is quite often all we can expect to get. An image delivered into Photoshop by the scanner or digital camera application software which is already in a device-independent colour space sRGB/Adobe RGB means that it has already undergone a considerable amount of data processing and not that itís an sRGB/Adobe RGB device.

Many Prosumer class scanners and digital printers are now supplied with some form of generic or "canned" profiles. Whilst these profiles are useable they are rarely accurate. For truly accurate colour matching you should seriously consider getting customised profiles for each device and/or media type. These profiles can be created professionally or by buying your own profiling software. Sadly very few, if any digital camera vendors have adopted the "canned" profile approach instead opting process the images into a device-independent colour space as discussed above.

Device profiles come in two basic forms, i.e. Input and Output. Input profiles typically describe the colour characteristics of scanners and digital cameras, whereas Output profiles describe devices such as monitors, printers and film recorders. Input profiles are often referred to as one-way since it is only possible to select them as the Source meaning we can never convert an image into the colour space of our scanner or digital camera. Output profiles are two-way meaning we can convert From or To them.

Why bother with Profiles?

Even though colour correction and colour management are not the same thing they are often confused with each other, especially by the novice Photoshop user. The colour characteristics of most imaging devices are such that it is very rare for them to be truly linear (i.e. R=G=B=Neutral). Sometimes this characteristic is referred to as the device not being well behaved. Scanners and printers are good examples of badly behaved devices. Obviously it would be extremely difficult for a Photoshop user to edit an image where a group of pixels with values of R=G=B=128 (grey) actually appeared to be non-neutral. In such circumstances colour correction would an absolute nightmare. To overcome these discrepancies we usually carry out all our editing in a colour space that is well behaved. In Photoshop well behaved colour spaces are more usually referred to as the Working Spaces, and are always characterised by having R=G=B appearing neutral. Without the aid of accurate device profiles the accurate translation of the raw colour data (the numbers) from the scanner/digital camera into the Working Space will prove very difficult, if not impossible. The translation from the Working Space into the media specific colour space of a digital printer will prove equally difficult without the aid of media specific printer profiles.

So the main benefit offered by colour management is that the process of colour correction can be undertaken in the knowledge that the image displayed on the monitor is an accurate visual representation of the original subject, and that the final print will accurately reflect the colours of the displayed image.

Some Photoshop Revision!

Photoshop CS continues to use document/image specific colour settings, which means that the colour space of each document is independent of others that may be open on the Photoshop desktop. As with Photoshop 6 and 7 the Working Space defined in Color Settings only has a bearing on three types of image, viz.: -

  1. New images/documents.

  2. Existing images/documents without an embedded ICC profile.

  3. Images/documents with no embedded ICC/ColorSync profile (i.e. untagged images/documents).

Image or document specific colour means that it's the profile embedded within an image that determines how the image will be displayed (it's appearance) and not the Photoshop Working Space. With Photoshop CS we can have multiple images, each in its own unique Working Space, open at the same time and each will be displayed accurately. Of course all of this assumes we're using a calibrated monitor.

Note that except for the obvious difference in user interfaces; Photoshop CS for Mac OSX and Windows share a virtually identical feature set. Therefore the Windows based screen shots that follow should be equally useful to Mac users.

On opening Photoshop CS for the very first time we are presented with an information dialog (shown below). The purpose of this dialog is to warn the user that the Photoshop Color Settings will be automatically configured or to provide access for manual setup. As with Photoshop 6 and 7  there is no wizard to help the user through the process of configuring the Color Settings. If Photoshop 6 and 7 are anything to go by many new users will panic at this dialog and accept the defaults only to realise later that this was only a short-term solution.

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For the purpose of this essay I to have chosen the No option and have therefore accepted the default Photoshop settings. However, I chose this option for no other reason than to concentrate upon monitor calibration and characterisation. Once I have discussed calibrating the monitor we can return to Color Settings.

Part 1 - Monitor Calibration and Characterisation

Accurately calibrating and characterising the monitor is the probably the most important aspect of the colour-managed workflow. The aim is to calibrate and characterise the monitor so that we eliminate unwanted colour casts and so obtain the best possible display environment for editing our images. We characterise the monitor by means of creating an ICC device profile, which is simply a data file that includes a description of the monitorsí colour handling characteristics. The profile will then be used by Photoshop to compensate for the colour limitations of the monitor. Photoshop automatically optimises the display of images by carrying out an on-the-fly conversion between the image/document profile (e.g. Adobe RGB, sRGB, ColorMatch) and the monitor profile. This conversion does not alter the actual image in any way.

Note: Adobe no longer supply Adobe Gamma with the Mac version of Photoshop although the Apple Display Calibrator Assistant found within System Preferences offers similar features. A tutorial describing the process of calibrating a display with the Apple Display Calibrator Assistant can be found here.

To calibrate and characterise the monitor Windows users should open the Adobe Gamma utility or a third party alternative. For many new users Adobe Gamma is more than sufficient and it's free.

Adobe Gamma is a Control Panel utility that can easiest be accessed from My Computer > Control Panel. Before running Adobe Gamma, it is best that the monitor has been switched on for at least 30 minutes. It is also best to work in subdued lighting when calibrating a monitor using Adobe Gamma. Another helpful tip is to set the desktop colour to grey.

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Control Panel as is appears when using the Windows Classic Theme

Step-by-Step Calibration

Step 1

When the Adobe Gamma utility is first opened you will be asked to make a choice between the Step- by- Step (Wizard) and the Control Panel method. It's probably easier to use the Step-by-Step (Wizard) method.

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Step 2

Using the Load button choose your monitor profile or pick one that's close. If in doubt choose the Adobe default monitor profile or even sRGB, it really makes little difference since all we are doing is defining the start point.

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Before progressing to the next step, be sure to give the profile a unique description and include the date.

Step 3

Set your monitor contrast control to maximum and then adjust the brightness control until the innermost grey square is only just visible against the black surround. Squinting your eyes helps with this process, as does keeping the room lighting at a low level or off.

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Step 4 

If you're using a manufacturer supplied profile for your specific make and model of monitor then in all probability the Phosphors will be listed as Custom. If this is the case leave well alone. If you don't have a monitor profile choose either Trinitron or P22-EBU. I keep getting asked -"how do I decide which is appropriate for my monitor?"  You can tell a Trinitron monitor by simply looking at the display area. A Trinitron type monitor will have two faint lines running across the display area approximately 1/4 from the top and 1/4 from the bottom. If your monitor has these lines choose Trinitron, otherwise choose P22-EBU.

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Step 5

Begin by keeping the View Single Gamma selected. However, keep in mind that this option ONLY allows you to adjust the relative brightness of the monitor.

Adjust the slider until the inner grey square blends with the outer frame, squinting slightly can help. Finally, deselect the View Single Gamma checkbox.

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Step 6

This is the step where we neutralise the colour imbalances inherent in our monitor. Adjust each of the sliders in turn so as to blend the inner square with its coloured surround. Again squinting is a great help.

Green is usually the most difficult to get right, but persevere. The closer you get to a perfect match at this point the more accurate your final profile will be.

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Step 7

Depending upon your computer type choose either the Windows Default or Mac Default gamma. In reality, this choice is not as important as it once was and you can choose either in the knowledge that Photoshop will make the appropriate corrections when necessary. Personally, and even though most of my work is now done on the Mac platform I choose gamma 2.2

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Step 8

Choosing the White Point for your monitor is pretty much a formality these days. Even the die-hards are in agreement that 6500oK is probably the best option on most systems.

You should have already set the Hardware white point via the dials/buttons on the monitor. Most monitors have a native white of 9300oK; so do check what it has been manually set to.

Choosing 6500oK provides the cleanest and brightest white point and closely matches daylight. If you feel really confident you could select the Measure option. You can choose 5000oK, but this usually produces a slightly dimmer and more yellow white point.

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Step 9

Generally, it's better to leave the Adjusted White Point setting at the default - Same as Hardware. Nevertheless, this option is used to choose a working white point for monitor if it differs from the hardware white point set in the last step.

By way of example; if your hardware white point can only be set to 6500oK, but you want to set it at 5000oK because that most closely represents the environment in which it will normally be viewed, you can set your Adjusted White Point to 5000oK, and Adobe Gamma will change the monitor display accordingly: However, choosing this approach will all cause the graphics card colour LUT to be adjusted quite severely, and depending upon the graphics card the screen can look quite ugly on some systems. As indicated above I recommend that you choose Same as Hardware and thus avoid this problem.

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Step 10

That's it, if all has gone well you will have adjusted the brightness, contrast and colour settings of your monitor to the optimum values.

Make a quick check using the Before and After radio button. If you're happy that the screen display now looks more neutral than before press the Finish button and Save the profile. Once saved the profile will be available for use by the OS and Photoshop.

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22 May 04

(Optional Steps)

Finally you might wish to check that the newly created monitor profile has been enabled and set as the system default. To do so you should reopen the Windows Control Panel from My Computer and double click the icon labelled Display. A dialog called Display Properties, which will be similar to the following should appear.

Once the Display Properties dialog box appears navigate your way to the Settings tab and click the Advanced button. The next dialog box to appear will be labelled to match with the display/graphics card vendor names and will be similar to that shown below. The final step is to click the tab labelled Color Management. All being well you should find that your newly created monitor profile is listed and set as the default.

Useful Information on location of  ICC/ColorSync Profiles

Photoshop CS is only compatible with Windows 2000 and XP on the PC platform and OSX 10.2.x or higher on the Mac platform. An upside of this change is that the ICC and ColorSync profiles are more easily found.

Profile locations:

Windows 2000 and  XP - sub-folder named system32/spool/drivers/color

Mac OSX - ColorSync profiles are located in the Library/ColorSync/Profiles folder

The only advantage of Adobe Gamma (Windows systems) or the Apple Display Calibrator Assistant (Mac OSX systems) is that they're both free, whereas the third party products can cost nearly as much if not more than Photoshop. However, since many third party alternatives use hardware and not the eyeball for measurement you are generally assured of much greater accuracy.

Part 2 - Photoshop CS Color Settings

Now begins the process of configuring Photoshop. This is achieved through the "Color Settings" dialog (figure 1) found under the "Edit" menu (Windows) or the Photoshop menu (Mac OSX).

The Color Settings dialog is the control room for the Photoshop CS colour management system, and like all control rooms it can appear complicated. The default colour setting is called: North America General Purpose Defaults, but this certainly isnít the best choice. So if the default isnít what is, and how do we make the necessary alterations?

I could answer the above question by simply writing US Prepress Defaults but doing so doesn't really help explain why. Therefore, I will work my way through each section of the Color Settings dialog in turn.

Note the Description box at the bottom of the dialog. As the mouse is moved across the various pop-up menus, etc. you should see a short but informative explanation of what each menu does. Also note the checkbox labelled Advanced Mode; it's probably best that you select it now. At least you'll now see everything that the Color Settings has to offer, even if some are only applicable to the most advanced of Photoshop users.

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Figure 1 - Photoshop CS Default Color Settings

The first section is labelled Settings and is a simple pop-up menu with a list of pre-set Photoshop settings plus any that you may have saved. You needn't worry too much about this section just yet.

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Figure 2

If you are upgrading from Photoshop 6 or 7 it should be a simple matter of selecting your previous saved setup. Notice that Adobe has retained the Colour Management Off option for those users who find the whole subject too complicated. However, whilst I don't recommend choosing this option I am aware that quite a few new Photoshop users working on the PC Windows platform find it the easiest to manage.

Working Spaces

The next section is labelled Working Spaces (figure 3), and as I discussed earlier the selections made here will determine the Working Space of certain types of image/document.

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Figure 3

There are four Working Space types in Photoshop: RGB, CMYK, Grey and Spot (occasionally called Modes because they appear under the Image>Mode menu). Since configuring the others follows a similar process I will concentrate mainly on the RGB Working Space.

Also note that the term Working Space should not be confused with Workspace. The term Workspace is used by Adobe to describe the layout of palettes, menu bars, etc whereas Working Space relates specifically to the various colour modes available in Photoshop.

RGB - Working Space

Clicking the RGB pop-up menu with the mouse will produce a list of options similar to that shown below. I chose Adobe RGB (1998) because it's the Working Space I settled on when using Photoshop 5. Notice that Adobe RGB (1998) appears within a group of four Working Spaces, each of which is device-independent. Typically sRGB will be confined to those users solely interested in web design, ColorMatch is a favoured choice of many Mac users and AppleRGB is apparently for Mac web design.

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Figure 4

If you look just above the four common Working Spaces you should also find options for Monitor RGB (green spot in the screenshot), and in the case of Mac systems ColorSync RGB. Monitor RGB is simply the colour space of your monitor as created by the Adobe Gamma utility or a 3rd party software/hardware combination.

It's often claimed that Photoshop CS has no obvious way of informing the user which monitor profile is actually being used. Well, a quick check for Monitor RGB in the RGB Working Space pop-up should be enough to put your mind at rest. If Monitor RGB is showing something other than the profile you created when calibrating the monitor it is essential that you investigate the reason and make the appropriate corrections. It is also possible to select your monitor space as the Photoshop Working Space, but this is not really a good idea. ColorSync RGB is only available to Mac users and will reflect the settings chosen as part of the ColorSync setup.

The actual list of options available for selection as Working Spaces differs depending on whether you activated Advanced Mode, or not. If you chose to activate Advanced Mode then the list of available RGB profiles will be quite extensive.

Additionally, if you had previously been using another Working Space such as BruceRGB then it should also appear as one of the options in this extended list. If it doesnít you can still create it yourself by choosing Custom (yellow spot in figure 4 above). The dialog box shown below appears and you simply type in the data as shown for the Primaries etc, but remember to give this new Working Space a name and click OK.

Bruce RGB

Figure 5 - Description of BruceRGB

Bruce Fraser originally developed BruceRGB around the time Photoshop 5 shipped but it has long since fallen out of favour by the majority of experienced Photoshop users.

CMYK - Working Space

With the exception of the list of available profiles making your choice of CMYK Working Space isn't that different to RGB. Again, having Advanced Mode activated gives you a more extensive list. Since desktop inkjet printers from Epson, Canon and HP actually require RGB data rather than CMYK and so configuring this particular Working Space will have little or no influence in their actual workflow.

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Figure 6

As mentioned above, the choice for you make is pretty much irrelevant if using a consumer class inkjet printer. In my case I just picked US. Web Coated (SWOP) V2. We can also have pick the old Photoshop 4 or 5 default CMYK options, the ColorSync settings (Mac only), or even customise our own settings.

Greyscale - Working Space

With the Greyscale Working Space we have access to two gamma settings, a series of five pre-set dot gain curves, the ColorSync Grey Work Space (Mac only) and the ability to customise the dot gain to our own requirements. The screenshots below (figures 7 and 8) show the various options and a typical customised Dot Gain curve.

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Figure 7

Note that if you choose to use a Custom Gamma or Dot Gain this will be the Working Space listed in the Grey Working Space pop-up menu.

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Figure 8

A very important point regarding Greyscale is that itís not tied to the CMYK setup! This is why some legacy greyscale documents might not look quite the same as they did in Photoshop 5.x (does anyone still use Photoshop 5?)

Spot - Working Space

The Spot pop-up menu is broadly similar to the greyscale, but for spot colours. The options that we find include a series of five pre-set Dot Gain options and the facility for customising the Dot Gain curve if required. In my case I simply selected the standard 20% option.

Colour Management Policies

Colour Management Policies was a new phrase introduced by Adobe with Photoshop 6 and continues with only minor changes in Photoshop CS. Figure 9 below shows the new default setup, but this hides a lot of important information.

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Figure 9 - Photoshop CS Defaults

This section of the essay is probably the one that will cause most Photoshop users the greatest difficulty and for that reason the explanation that I give below will appear quite wordy, but don't be put off.

Basically each Working Space will have the same set of three options, although we need not configure each identically. These options are called Policies and include: -

(a) Off

In simple terms, the Off Policy ensures that Photoshop does as little as possible when dealing with ICC profiles. In most circumstances it isn't the ideal choice and certainly not the choice to be made by new users. The following explanation will give you some idea as to the behaviour of Photoshop CS when this option is selected.

  • Choosing Off means that new images/documents will be created and saved without an embedded ICC profile. We sometimes refer to them as untagged images because they do not contain an embedded ICC profile.

  • Opening an existing image that has an embedded ICC profile matching the current Working Space will mean that Photoshop will honour the embedded profile and will subsequently be resaved with the image.

  • The default Pasting behaviour between images is to retain numerical values (RGB pixel values), not the appearance. This means that no conversion between colour spaces will take place and will often lead to the pasted version of the image taking on a radically different colour appearance to that of the original.

  • Opening an existing image that has an embedded ICC profile that does not match the current Working Space (i.e. profile mismatch) will cause that embedded profile to be stripped out of the image. The image will subsequently be saved with no embedded profile. With the Off Policy we find that the profile warning Ask When Opening has not been activated for Profile Mismatches so a warning similar to the following (figure 10) will appear.

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Figure 10

The problem with this configuration is that the user either accepts what Photoshop CS dictates or doesn't open the image at all, not much of a choice. Activating the Don't show again checkbox is generally accepted as a good move.

(b) Preserve Embedded Profiles (Default)

For most situations this is my preferred colour management policy since it offers the greatest degree of flexibility. The following should give you an idea as to the behaviour of Photoshop CS when this policy is selected.

  • Choosing Preserve Embedded Profiles means that when you open an existing image into Photoshop which has an embedded ICC profile that differs from the current Working Space then that image and its associated profile will be left intact. In other words Photoshop will make no attempt to convert the image to the current Working Space; the original embedded profile will be retained and subsequently saved with the image. Nevertheless, even though the image and Photoshop are no longer in sync colour space wise the image preview will still be accurate.

  • When opening an existing image with an embedded ICC profile that matches the current Working Space Photoshop will take no action; the image is opened and saved as normal.

  • The default behaviour when pasting either an RGB or Greyscale image is slightly more complex whereby the appearance of the pasted image will be preserved but the numbers will change (i.e. the pixel values will change). In the case of CMYK it is the numbers that will be retained, not the appearance.

  • If the image being opened or imported has no embedded ICC profile (i.e. the image is untagged) then Photoshop will use the current Working Space for editing and previewing purposes. However, the profile will not be embedded into the image when it is subsequently saved.

  • Creating a new document with this policy setting means that the current Working Space is used for editing, previewing. The associated profile will eventually be embedded into the file when saved. However, the default Working Space profile for new documents can be overridden in the New document dialog.

The following warning (figure 11) will appear if the profile warning Ask When Opening has not been activated for Profile Mismatches. Again, my earlier comment about Photoshop imposing its will on proceedings applies.

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Figure 11

At first glance the above warning appears virtually identical to that shown for the OFF Policy, but there is a subtle difference - the embedded ICC profile is retained rather than discarded. Compare the text of the two screenshots (figure 10 and 11) if you're in any doubt as to the differences. Again you may wish to tick the Don't show again checkbox so as to stop this warning reappearing in the future.

(c) Convert to Working Space

This policy behaves in an almost identical fashion to colour management Photoshop 5. It's for this reason that many still tend to favour it. Actually this policy isn't a bad choice but does need to be treated with care.

  • If an existing image with no embedded ICC profile is opened or imported into Photoshop then the current Working Space will be used for editing and previewing. However, there will be no profile embedded into the image when it is saved (i.e. the resulting image will be untagged).

  • If an image is opened or imported and has an embedded ICC profile which is found to differ from the current Working Space then that image will be converted into, and subsequently saved in the Working Space. When the image and the Working Space are matched then Photoshop takes no action; the image is opened and saved as normal. Newly created images will be edited, previewed and ultimately saved in the current Working Space.

  • Finally, the default pasting behaviour is to convert and thus preserve the appearance of the image. However, the user will get the option not to convert the pasted image, hence preserving the numbers if the pasted image doesn't match with the target image. Overriding the Default Policy Behaviour

Overriding the Default Policy Behaviour

The previous section described how our choice of Colour Management Policy determined the default behaviour of Photoshop CS under various scenarios. However, we need not be confined to these pre-set outcomes. A much better option would be to configure the Colour Management Policies as shown in figure 12 below.

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Figure 12

Here we can see that each of the checkboxes for Profile Mismatches and Missing Profiles be set for Ask When Opening or Ask When Pasting as appropriate. It is only through setting these checkboxes to ON that we can enable the default behaviour override facility.

Basically the three checkboxes associated with the profile warnings have the following impact on the Colour Management Policies: -

(i) Profile Mismatches: Ask When Opening

Photoshop has been set to present the user with a warning when the image being opened or imported has an embedded profile that does not match the current Working Space. The warning looks like figure 13 below and contains three options with the pre-set selection being dependent upon the Colour Management Policy in operation at the time. Noticed that all the necessary information required to make an informed decision is present.

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Figure 13

The above example is pre-set for how the dialog would appear when the Colour Management Policy is set for Preserve Embedded Profile. The user can choose to leave the image as is (default - Use the embedded profile), allow the conversion (Convert document's colors to the Working Space) or strip out the embedded profile and switch off colour management (Discard the embedded profile). Had the policy been Convert to Working Space the dialog would have looked almost identical except that it would have been pre-set for Convert document's colours to Working Space. Basically, the answer to the question: How do you want to proceed? is already decided for you when the Embedded Profile Mismatch dialog appears. If you KNOW this answer to be incorrect then by all means make an alternative selection otherwise leave well alone and click OK.

I think you will agree that the warning in figure 13 is a lot more user friendly than the one that appears under similar circumstances when Ask When Opening is unchecked (i.e. figure 10 above). At least with this option we now have the opportunity to assign an alternative profile to the image before it opens.

Now that Photoshop CS can read the EXIF colour space information it's likely that many consumer class digital camera users will be seeing this particular warning on a regular basis. Since no benefit will be gained by converting the image from say sRGB to Adobe RGB (1998) the best choice in such circumstances is to leave the default Use the Embedded Profile rather than be tempted to choose Convert document's colours to Working Space.

Users of high-end cameras such as the Canon EOS 1 or Nikon D series have the facility to program the camera so that it processes images into a colour space such Adobe RGB (1998). In this situation the user will know that the profile mismatch warning is incorrect and should choose to either accept the embedded profile or discard it. However, they must then use the Assign Profile command to assign the correct profile. Both methods are equally valid. Assign Profile does not change the actual image only its appearance. Assign Profile and Convert to Profile are discussed later.

(ii) Missing Profiles: Ask When Opening

Choosing this option means that Photoshop has been set to present the user with a warning when the image being opened has no embedded ICC profile. The warning looks similar to the following (figure 14) and again contains three options. The pre-set or default selection is dependent upon the Colour Management Policy in operation at the time.

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Figure 14

The above example is pre-set for how the dialog would appear when the Colour Management Policy is set for Preserve Embedded Profile. Since no profile is embedded Photoshop will try to assign the Working Space profile to the image. No conversion takes place, just the assignment of the Working Space profile.

The lower Assign Profile (and the associated and then convert to working RGB) checkbox is the best choice if you know the source images' true colour space and you want the image to appear correctly in Photoshop. Typically, this option will be used for images from a digital camera or similar device that does not embed a profile in the image file or provide accurate EXIF colour space information. Note that the source profile must be known and available to the user before this option can be selected.

(iii) Paste Profile Mismatches: Ask When Opening

Figure 15 below shows the Paste Profile Mismatch warning that appears in the event of the colour spaces of the two images not matching.

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Figure 15

Note that the terms preserve colour appearance and colour numbers relate to the source image, not the destination.

The various warning dialog boxes shown above are only a sample of those that may appear as you open or import images that contravene the defined Colour Management Policy. However, I think that the text messages included in each should be more than ample to explain what each option does and will therefore allow you to make the appropriate choice.

Conversion Options

This section will only be present in the Color Setting dialog if the user chooses to activate the Advanced checkbox. Figure 16 shows this section of the Color Setting dialog in its default configuration.

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Figure 16

Engine: this is the name of the engine, which will be used for all colour space conversions. Unless you have good reason to choose an alternative your should leave it at the default Adobe ACE setting. ACE is the direct equivalent of the Built-in engine used in Photoshop 5. Windows users should NOT be tempted to choose ICM. Mac users should keep in mind that the option chosen here will override the selection made in the ColorSync setup. Choosing the ColorSync engine is for Mac users as a bad a choice as Windows users choosing ICM.

Intent: this pop-up menu allows the user to select from four different rendering intents, namely Perceptual, Saturation, Relative Colorimetric and Absolute Colorimetric. Typically, most users will choose between either Relative Colorimetric or Perceptual. A short description on each is provided in the Description section of the Colour Settings dialog. A more comprehensive explanation can be found in the Photoshop on-line help files.

With Relative Colorimetric it is only those source colours that are out of gamut (i.e. can't be viewed/printed accurately within the destination colour space) that will be mapped to the closest in-gamut colour, the remainder are left unchanged. This means that in the case of images with lots of out-of-gamut colours the visual relationship between the colours (after conversion) will almost certainly change. With Perceptual, all colours of the source colour space will be mapped to the nearest in-gamut colour of the destination colour space thus maintaining the visual relationship between colours. In other words, with Perceptual the whole image colour gamut will be compressed so that it fits within the new colour space. The Photoshop default and my recommendation is Relative Colorimetric.

Use Black Point Compensation: this should be kept checked. Black Point Compensation ensures that the darkest neutrals of the source colour space are mapped to the darkest neutrals of the destination colour space. In most circumstances toggling BPC ON and OFF will result in no obvious change to the image appearance.

Use Dither (8-bit/channel images): as with Black Point Compensation this should be kept checked. The description box at the bottom of the Colour Settings dialog box will give you some clue as to what it does.

Advanced Controls

As with the Conversion options, this section will only be present in the Colour Settings dialog if the user chooses to activate the Advanced checkbox. Figure 17 shows this section of the Colour Settings dialog in its default configuration.

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Figure 17

An explanation on what each of these options do is provided in the Description box and on-line helps files. The consensus appears to be that both settings should be left in the default Off condition.

The Desaturate Monitor Colour option is the one that has greatest potential to cause confusion, as it will result in the image preview to become progressively less saturated as the percentage is increased. Those choosing to work in VERY wide colour spaces may find it useful, however, the majority of Photoshop users should leave it Off.

Saving Out Your Own Default Colour Settings

Select the Save button and give your settings a Name and Description by which you can call them back in the future, if for some reason you make a temporary change. Also note that you can have as many different sets of settings as you wish, although only one can be active at a time. Figure 18 shows my preferred colour settings. Notice that I have chosen to use a customised dot gain for the greyscale Working Space; you shouldn't try to repeat these particular settings since it is specific to my workflow.

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Figure 18 - Customised Color Settings Configuration

Part 3 - Soft Proofing

A frequently asked Photoshop questions is: why don't my prints match the screen? Generally it's down to poor monitor calibration, but on other occasions it's simply the fact that the user has unrealistically high expectations of what can be printed or theyíve made the wrong selection in the Photoshop Print with Preview dialog.

This section will discuss the options and commands associated with the Photoshop CS Soft Proof feature and should also go some way to answering the above question. However, you should note that I haven't included any reference to specific printer driver set-ups as these have been covered in a dedicated tutorial at: - Managing colour when printing

Basically soft proofing is nothing more than using your monitor as a proofing device. However, accurate proofing is dependent upon the quality and accuracy of the monitor profile that I described in Part 1. Youíll also need good quality media profiles for each printer/media/ink combination.

In order that we may get Photoshop in a state ready for soft proofing we must configure the relevant dialogs. This is done via the View > Proof Setup > Custom menu as shown below.

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Proof Setup only affects the current or active image on your desktop. So if you want to define your own default Proof Setup (as wise move) you MUST configure the proof setup via the Custom menu option with NO image/document open.

The various proofing options are:

  • Working CMYK - soft proofs the image using the current CMYK working space defined in the Colour Settings dialog.

  • Working Cyan, Magenta, Yellow and Black Plate or Working CMY Plates - soft proofs the image using the current CMYK working space defined in the Colour Settings dialog.

  • Macintosh RGB and Windows RGB - soft proofs the image using the standard Mac or Windows monitor profile (i.e. Apple RGB and sRGB respectively).

  • Monitor RGB - soft proofs the image using your actual monitor profile. If the image look bad when this option is selected you know that your monitor profile is broken and needs to be recreated as described in Part 1.

  • Simulate Paper White - provides a preview of the shade of white for the paper based upon the active soft proof profile . This option requires a very accurate profile otherwise the whites of the image can appear significantly more blue/yellow than it should.

  • Simulate Ink Black - provides a preview of the dynamic range of the image based upon the active soft proof profile.

The screenshot below shows a typical view of the Proof Setup dialog for an Epson inkjet printer simulation. From this dialog we can easily select, configure and save our own customised soft proofing setup for any number of different printer profiles. Remember; make sure you have NO images/documents open when going through the process of defining your own default Soft Proof profile.

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We begin the process by choosing the Profile; in the example shown above I have selected the Epson profile for Premium Glossy paper. This choice will be the profile for the media that we want to simulate on the monitor.

Preserve Colour Numbers

This option will only be available if the image and profiles are in sync, i.e. both are RGB or both are CMYK. Selecting the Preserve Colour Numbers checkbox will usually result in a quite awful looking display, this is how it should be. Basically we are simulating how the document/image will appear if it is not converted to the actual device profile.

One use of this option is to enable you to see how the image would print if the media profile had not been selected in the Profile pop-up menu. There are apparently others, but these all well beyond my understanding. Normally it is best the leave the checkbox unchecked.

Use Black Point Compensation

I described Use Black Point Compensation previously when discussing the Conversion Engines. Typically, it will be best to keep it checked.

Intent

Intent is the setting that appears to cause most confusion and it's generally worth trying both Relative Colorimetric and Perceptual. Typically Relative Colorimetric will be best but some highly saturated images may benefit from choosing Perceptual.

Simulate

There are two options (or checkboxes) shown in this section of the Proof Setup dialog. The first Paper White allows you to simulate, on the monitor, the shade/colour of the paper white. The second Ink Black will enable you to simulate, on your monitor, the dynamic range defined by the media profile (i.e. how dark black will appear on the media you are printing to). Note that selecting the Paper White checkbox will cause the Ink Black to be selected and greyed out. Not all profiles will support both options.

The resulting soft proof display can be quite disconcerting in that the overall tone of the image may tend to look compressed or slightly colour shifted (e.g. white takes on a blue cast). This can often occur when using scanner derived printer profiles. In such circumstances it may be best to ignore the use of the Paper White and Ink Black since it is VERY unlikely that they are in fact providing an accurate soft proof. No doubt things will improve as the suppliers of the profiling software update their programs to be compatible with this Photoshop feature.

To save your customised proof setup simply choose the Save button and give the soft proof profile a name that clearly indicates the printer/media combination for which it should be used. The name of a saved soft profile will be appended onto the bottom of the list immediately below Simulate Ink Black.

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The saved soft proof profiles are saved to the following locations:

Windows - Program Files/Common Files/Adobe/Color/Proofing folder

Mac OSX - ~Library/Application Support/Adobe/Color/Proofing folder

A comprehensive tutorial describing the technique of soft proofing is provided here

Part 4 - Managing Image/Document Colour Space

On the Colour Space conversion and profile-embedding front we find that little has changed from Photoshop 6 and 7. Without the tools that follow it would be virtually impossible for the user to maintain a fully colour-managed workflow.

Assign Profile

As with previous versions of Photoshop the Assign Profile command is accessed via the Image > Mode menu and allows the user to assign any profile of their choosing to an image. The command itself was designed for only a few limited uses, typically with images that have been scanned into Photoshop using a Twain module or a scanner package that has no means of embedding an ICC profile. It will also be useful handling images from digital cameras that have no embedded profile or incorrect EXIF colour space information.

Assuming that the colour management policy is not set to off then an image imported into Photoshop with NO embedded profile will be assigned, previewed and subsequently saved using the current Photoshop Working Space. Obviously, this may not be the most appropriate colour space in which to edit or save the image; so assuming the user has the correct source profile they can make Assign the correct profile.

Itís important to note that assigning a profile does NOT convert the image (will not change the numbers; i.e. RGB pixel values). Assign simply provides Photoshop with a description of the actual colour space that you wish to edit and view the image in. In other words it changes the image appearance or meaning of the numbers.

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  • The Don't Colour Manage this Document: option is used to instruct Photoshop to remove an existing embedded profile (sometimes referred to as untagging).

  • The Working RGB: option tags the image with the current default working space profile as defined in Colour Settings.

  • The Profile: popup option allows us to assign a profile other than the default Working RGB profile. In the above example I chose to assign a customised profile for a digital camera.

Other potential uses for Assign Profile include the removal of an embedded profile (i.e. don't colour manage the image). The example screenshot shows a case where I chose to assign a customised profile for my digital camera to an image.

Convert to Profile

The Convert to Profile command found under the Image > Mode menu is basically an enhanced version of the old Photoshop 5 Profile-to-Profile command. With Profile-to-Profile we were able to define the source colour space (and probably get it wrong) whereas in Photoshop CS this cannot be done since the source profile for the image is locked. The only way that this source profile can be changed is via the Assign Profile command discussed previously.

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In the example above I show an image with an embedded profile (Source Space = Canon EOS D30 ..........NSC) being converted to Adobe RGB (1998) (i.e. the Destination Space). Whenever we make this conversion it will be the profile for the destination space that is embedded within the image file when saved. Convert to Profile changes the numbers (i.e. pixel values). The inclusion of the Preview checkbox allows the user to compare the conversion with and without Black Point Compensation, Dithering and any one of the four rendering Intents. The ability to preview the conversion is a real boon and shouldn't be ignored, use it to your benefit.

Notice that the Intent is set to Relative Colorimetric, as this was the default Intent chosen by me when configuring the Color Settings. However, as with many Photoshop setting the Intent is "sticky", which means that if I had chosen Perceptual instead then the next time I chose Convert to Profile the Intent would be set to Perceptual. The moral being - always check the actual value before clicking OK.

Save As

Last but not least, the Save As dialog throws up a host of useful features. The Embed Profile checkbox is very important and will reflect your choice of Colour Management Policy. You switch it ON or turn it OFF as you please, the latter option being a bad idea in most instances. Notice that the dialog even informs us which profile is being embedded.

The screenshot shown below is how the dialog appears on a Windows 2000 system; the Mac OSX version of Photoshop CS will look slightly different, but are functionally identical.

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The other save options present in the dialog are those associated with Layers, Alpha Channels, Annotations, etc. Again, we can choose to uncheck them and so save the image without the layers, etc. The Save As a Copy feature is engaged by default as soon as you uncheck Layers; this prevents you trashing a lot of hard work.

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Part 5 - Print with Preview

Whilst printing from within Photoshop is discussed in separate tutorial it's still worth providing a brief overview to round off this essay on colour management.

The screenshot shown below shows the colour management features within the Print with Preview dialog box although it is first necessary to turn them on via the Show More Options checkbox. The various colour management options enable you to define the source and destination (target) colour spaces and the rendering intent used to convert the image between the two.

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Source Space: Document - this denotes the actual colour space of the source image/document to be printed. The above example shows Adobe RGB (1998), but it could be any number of user specified alternatives (e.g. sRGB, ProPhoto, ColorMatch, etc.). If the image has already been converted (using the Photoshop Convert to Profile command) to a printer/media profile its name will be reflected here.

Source Space: Proof - tells Photoshop to convert the image/document from the source colour space to the ICC profile specified in the Proof Setup dialog (see: Photoshop View menu).

Print Space: Profile - is where you choose the preferred method of managing the colour output from Photoshop. We have three different options - each has its own specific configuration in the printer driver so avoid a mix and match approach, as it will end in tears. The following discussion should help you understand the differences between each.

  1. Same as source: Photoshop simply passes the image/document straight to the printer driver without making any print space conversions. This option is effectively telling Photoshop to not colour manage the printing of the image/document.

  2. Printer Colour Management: choosing this options tells Photoshop that the image/document should be sent to printer driver with the profile listed against Source Space: embedded within it. By embedding the profile Photoshop is providing the printer driver with all the necessary information required to ensure accurate colour rendering. Image/document colour management is handled the printer driver.

  3. ICC Profile: this last option is where we choose a specific profile that is compatible with our printer. Notice that once an ICC profile is selected the Intent and Use Black Point Compensation (BPC) facilities are activated.

Hopefully the material presented in this essay has been helpful and improved your understanding of Photoshop's approach to managing colour. As noted throughout the essay there is vast body of material to be found all over the internet. A simple search using "google.com" and the keys words color management is all that is required.

 

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