Header
 

 

Title

By

Ian Lyons

A Computer Darkroom Review

Prior to the introduction of Photoshop 5 by Adobe, users of Microsoft Windows 95/98 had no real knowledge or experience of "Colour Management". Yes, most of us were familiar with the terms ICM and ICC, but in truth we saw very little evidence of its true power and functionality. On the other hand Mac users have had access to a system level colour management system for years in the form of "ColorSync". Even then many of the concepts and procedures introduced by Photoshop 5 have required a different approach from those of previous versions.

 

1. What's all the Fuss About

In truth, and for many, colour management is of no great importance, but for photographers and anyone else interested in the accurate reproduction of colour in print or on screen, it is one of the most vitally important features introduced by Adobe as part of Photoshop 5.

One of the most often raised issues relating to Photoshop is – "why don’t the printed colours match the colours displayed on screen?" Epson claim in one of their online support documents that the answer is quite simple - "because monitors and printers use different technologies to create colour". They go on to say - "no monitor will ever match the printed piece of ANY printer due to the fact that the human eye perceives colour completely different when looking at colour reflecting off paper or projection from colour monitors". However, this is only partially true, by ensuring that Photoshop is correctly configured it is possible to achieve "acceptably" accurate colour matched prints with only minimum effort.

This article explains the process of configuring the colour management system within Photoshop 5 for those aiming to optimise the RGB workflow required for making prints that come "acceptably" close to matching their on screen image when using inkjet printers from manufacturers such as Canon, Epson and Hewlett Packard.

Obviously, in the limited space available it is not possible to address all the issues pertaining to colour management. For those wishing to gain a better understanding of how colour management works within Photoshop 5 you should follow this link to Adobes On-line Guidance Documents:-

http://www.adobe.com/

Further information can also be obtained from Andrew Rodney's web site at:-

http://www.digitaldog.net/tips.html

 

The final section of this article deals with colour correction. Although not strictly speaking anything to do with colour management, I believe you will find it informative if not entertaining?

2. The Colour-managed Workflow

The purpose of a Colour Management System (CMS) is to maintain a consistent  "appearance" of any given colour on different devices (i.e.; scanners, monitors, printers, etc.) throughout our system. In order that we may achieve this it is first necessary for each device to provide the Photoshop Colour Matching Engine or Module (CMM) with some information on how colour behaves within that device, and this is provided through "Device Profiles".

A typical "Colour-managed Workflow" will involve image input via a scanner or Photo CD, being viewed on the monitor, with colour correction of images on the computer, and image output to a printer or film recorder. As the image data is passed along the chain - from scanner - to - computer - to - monitor - and printer, colour inaccuracies will be introduced. These inaccuracies result primarily from the widely differing colour spaces or gamut's of each device. To minimise these inaccuracies we must give the CMS information in the form of device "Profiles" that describe the colour gamut of each device. Using these profiles the CMS is provided with information that says for example,  "this RGB image data is from such and such a scanner, which sees colour in this way", the CMS will then know exactly what colour really looks like on that scanner. Likewise for our monitor or printer, again with suitable profiles the CMS will adjust the scanner image data into a form that the monitor or printer can show accurately.

Most devices are supplied with generic or "Canned" profiles that describe them pretty well, but for truly accurate colour matching you should seriously consider either getting "Customised" profiles for each device done professionally or buying your own profiling software (e.g. ColorVision Photo/OptiCAL, Praxisoft WiziWYG or Monaco Systems EZcolor).

Image

A Typical Colour Managed Workflow

It is also worth pointing out that whilst most low cost, consumer based film and flatbed scanner applications are ICC aware they tend to impose sRGB as the "Source" colour space. This colour space is not ideal for anybody seriously interested in obtaining high quality prints or film output from within Photoshop, in so far as its colour gamut is so limited. Some manufacturers i.e. Nikon, Polaroid and MicroTek allow us to scan and save our images in any "Target" colour space we choose. Unfortunately others make similar claims but in reality the "Source" colour space is generally always "sRGB". Furthermore, the image is rarely if ever "tagged" with a profile of any description, so the file contains no information relating to the profile upon which it is based.

3. Monitor Calibration

Having first installed Photoshop 5 on your computer the next task is to make sure your monitor is properly calibrated. If the  monitor is not correctly calibrated then we can have no confidence in the on screen colours being a true representation of the image data. Accurately calibrating your monitor is also an essential (if not critical) first step in developing a colour-managed workflow. For real accuracy we would normally wish to use a specialist hardware device, but these tend to be expensive. However, Adobe has provided us with an acceptable software solution for this purpose, namely "Adobe Gamma", although others are available see  (http://www.colorcal.com) for details.

The following information concerning monitor calibration is applicable only to Windows 98, Windows 98 Second Edition and Windows 2000. Users of Mac systems may find the procedure to be identical, but the dialogs will look slightly different.

"Adobe Gamma" can be accessed either through the Windows Control Panel Folder or via Photoshop's Help Menu and selecting "Colour Management". To be honest I don't like the Help version of accessing Adobe Gamma since part of the process involves overwriting ALL the hard work of RGB setup etc. (see later).

Image

"Adobe Gamma" is used to calibrate your monitor at "System Level" and thus ensures that unwanted colourcasts associated with your monitor are eliminated. The profile created as part of the calibration process becomes the "default profile" for your monitor and is also available for all other applications that can use ICC profiles. This new "Custom" profile is generally referred to as your "Monitor Space", and is unique to "YOUR" monitor. It is important to note that:- no matter what software application you are using, the image on screen is always being viewed in "Monitor Space".

A further point worth considering is your working environment. Calibrating a monitor during daytime and using it later in an artificially lit room is pointless, since your perception of colour in natural light is entirely different from that in artificial light. So consider carefully how, where and when you set up your system. A consistent environment is an essential prerequisite for accurate colour matching.

You should use a neutral background for the Windows desktop, and all screen savers and power management features should be turned off (and kept “off”). Allow at least 30 minutes after first switching on your monitor before commencing the calibration process. Set the white point of your monitor. This is a hardware adjustment, and how you do it depends on the monitor you are using. Most monitors have a control panel. If you're unsure how to set the white point on your monitor, consult the documentation that came with it.

Before we begin the process of calibrating the monitor check to see if "Adobe Gamma Loader.Exe" or a short cut to it is in your "Start Up" Folder.  The Windows 98/98SE Start Up folder is nested below the "windows/start menu/programs/startup" folder.

For Windows 2000 things are a little more complicated in that the "start up" folder is found deep down the tree in the "Documents and Settings" folder, and worse still each user has his/her own set of folders - you'll need to find it yourself!!! 

If after checking you can't find "Adobe gamma Loader.Exe" in the relevant folder; then you can make a "Shortcut" to the file, it is found in the "Program files/Common Files/Adobe/Calibration" folder (this assumes Windows based computer).

The following page outlines the various steps in calibrating your monitor based upon Adobe's recommended procedure and my own experience.

Step by step monitor calibration using Adobe Gamma

Step 1

On opening Adobe Gamma I recommend selecting the Step By Step or (Wizard) option. You should then follow the on screen instructions.

Image

Step 2

Adobe Gamma then tells us the profile upon which the subsequent calibration process will be performed.

Image

Adobe Gamma Profile selection dialog for Photoshop 5.5

Searching out a Profile specific to make and model of monitor is to a very large extent a waste of time, most are pretty awful, so if you don't have one don't panic.

Normally the first time you use "Adobe Gamma" the profile initially offered is the standard "Adobe Monitor Profile". We don’t have to accept this profile, we can actually select any monitor profile we want, but realistically it’s as good a starting point as any. In fact if you are using Adobe Photoshop V5.5 it is MOST DEFINITELY the place to start. Without going into unnecessary detail it is recognised that many manufacturer based monitor profiles are incompatible with the Photoshop 5.5 version of Adobe Gamma. In fact this is one of the reasons underlying some people finding it virtually impossible to get a good screen-to- print match. If you have a version of Photoshop prior to V5.5 then the problem with Adobe Gamma and manufacturer supplied profiles shouldn't be a problem.

Profiles locations:-

Windows 98 and 98 Second Edition - folder named windows/system/color

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

Mac - ColorSync profiles are located in the System Folder/ColorSync Profiles folder

The dialog window shown above is unique to Photoshop 5.5 in that earlier versions don't have the "Description" window. This new window is actually quite important in that you can edit the monitor profile name. In fact I recommend that you do precisely that, otherwise the name shown will stay with the profile and cause you utter confusion next time open the Photoshop (e.g. - "Photoshop my profile says its sRGB, but I know it isn't"). Simply type the new name for your monitor profile and then select "Next".

If you have already calibrated your monitor using a manufacturer based ICM profile and would prefer to recalibrate using the above method then simply remove the old monitor profile from the relevant location as indicated below:-

The amount of adjustment required in the steps that follow will vary, depending upon how far your monitors’ actual behavior deviates from this initial profile.

Step 3

The next step is to adjust the contrast and brightness levels of your monitor.

Image

My recommendation is that the brightness should be adjusted so that the inner square is only just visible (as an aid I suggest that you squint when you make this adjustment). If the on screen image looks a shade dark after this stage don’t be too concerned, it will be corrected during the gamma adjustment stage. In fact, I have found that unless the screen is dim (at this stage), then the likelihood of over dark prints is increased significantly, so be warned!

Step 4

Once the brightness and contrast have been adjusted we move on to the monitor phosphor selection.

Image

We can either accept whatever is offered up in the window, not a good idea, you should select  Trinitron or P22-EBU, both of which are based upon standard monitors. Although, it is fairly widely accepted that Trinitron is probably the better starting point. The amount of adjustment required in the steps that follow will vary, depending upon how far your monitors' actual behavior deviates from this initial profile.

You can also choose "Custom" and insert our own values; normally you would need to have obtained the values from the manufacturer, not and easy task, and pointless. Don't forget that using the manufacturers ACTUAL ICM profile in Photoshop 5.5  is fraught with dangers.

Image

Custom Phosphor data (sample only!)

Step 5

Next we adjust the gamma slider (I suggest that you stick with the single gamma option initially, just to get the hang of things). When adjusting this slider I recommend that you sit back about 3 feet from the monitor and squint your eyes. When the inner square matches the outer patterned frame, stop. Choose your desired gamma (usually 2.2 for Windows) and then fine tune the gamma slider. If all has gone well your screen should now be reasonably bright, but not to bright.

A common misconception is that the gamma must be set to 2.2. Please note that there is no absolute requirement that the gamma be set to this value. If the user prefers to select a gamma value of 1.8 then that is perfectly reasonable choice, it is also the case that many actually prefer to calibrate their monitors to a gamma of 1.8 when CMYK prints are the final output medium. Mac users will generally find 1.8 is the more appropriate choice for their systems since it is apparently the native gamma of Mac monitor. I use both Mac and PC and find that I personally prefer Gamma 2.2 is the most appropriate.

Image

Once you become confident in using the single gamma option you can try the 3 channel option and balance each colour channel independently, this actually the best way. The procedure for balancing the inner and outer squares is the same as described above, although many people find it difficult at first to get the "green" square right.

Image

Step 6

If you are in any doubt about the accuracy of the  "Hardware White Point" you selected on the monitor control panel at the beginning then it might be better to use the "Measure" option (ensure that the room lights are off for this adjustment).

Image

Image

Adobe Gamma Monitor Colour Temperature Adjustment

The idea of the colour temp screen is to get the centre square as near neutral grey as possible. Keeping a Kodak grey card to hand can be helpful, but not essential.

For the "Adjusted White Point" it is normally accepted practice to choose "6500K"if using a PC or Mac. As was the case with gamma, it is not essential that we follow conventional wisdom when it comes to setting the White Point of your monitor. I have found a more appropriate choice to be  "Same as Hardware", since this doesn't actually require the video card to make any colour table adjustments (see Real Word Photoshop 5).

Image

Preferred choice for Adjusted White Point

Step 7

The final step of the monitor calibration process is to "Save" your new monitor profile. Remember this is now the profile that defines your "Monitor Space" and is used by all your software applications, including most scanner software, whether be it be "Standalone" or a "Twain plug-in".

4. Colour Settings

The previous section concentrated upon how we see colour on the monitor and how accurate that representation of colour actually is. The "Color Settings" menu option found under the "File" menu is where we effectively tell "Photoshop" what red, green, blue, cyan, magenta and yellow actually look like, and how we want the colour management system therein to operate on these colours.

Image

(i) RGB Setup

The RGB setup dialog is where we define the Photoshop RGB "Work Space". Just to confuse matters it’s also known the "Editing Space", or "Colour Space", I'll be using the three terms interchangeably.

The work space selected here is normally considered "device independent" (i.e. independent of scanner, monitor or printer devices), and allows Photoshop to attach a specific colour meaning to our RGB data.

Remember also that unless you specify otherwise the RGB work space (profile) selected by you here is the profile that will be saved with your file (i.e.; "tagged").

Before we begin selecting our preferred RGB work space I will dispel a commonly held misconception, namely that the gamma and white point selected for the RGB work space must be the same as we have chosen when calibrating our monitor, wrong!, simply because the two are NOT related. There is absolutely no reason why you should keep both compatible.

Image

There are nine "Canned" RGB colour spaces supplied as standard with Photoshop 5, each of which is based upon industry standards. There is also the option to select your "monitor space" (i.e. Monitor RGB) or define your own "Customised" RGB work space.

The selection of Monitor RGB is not recommended since it is not "device independent", but most importantly, monitors cannot display a considerable part of the gamut of CMYK output devices such as our inkjet printers.

Image

Of the nine "canned" RGB colour spaces there are only three that are truly useful to most of us printing to inkjet printers, namely:

  • Adobe RGB (1998) – based upon a gamma of 2.2 and a White Point of 6500K, which is broadly compatible with daylight in shade. This colour space comes very close to encompassing the entire CMYK gamut, although it has some difficulty with greens. Its gamma value of 2.2 ensures adequate separation of shadow detail is maintained.

  • ColorMatch RGB – this RGB colour space is based upon a gamma of 1.8 and a White Point of 5000K. It is also widely used by Mac users, and has slightly narrower colour gamut than Adobe RGB. Its main drawback relates to the gamma value of 1.8, which can cause some posterisation problems in shadow areas. That said it is still a perfectly acceptable workspace on either the PC or Mac platforms.

  • sRGB – this RGB colour space is similar to Adobe RGB above in that it is based upon a gamma of 2.2 and a White Point of 6500K. However, the colour gamut of this space is somewhat limited and can only be recommended for use with the 4-colour range of inkjet printers from Epson, Canon, HP, etc. It is also widely used for web pages, etc.

With the "Custom" option we can define our own RGB colour space, although this doesn’t come highly recommended. That said there is one custom colour space that has almost become an industry standard, i.e. "BruceRGB". The specification for this work space is as follows:-

  • White Point = 6500K

  • Gamma = 2.2

  • Red Primary xy = 0.6400, 0.3300

  • Green Primary xy = 0.2800, 0.6500

  • Blue Primary xy = 0.1500, 0.0600

This colour space has all the advantages of Adobe RGB (1998) but doesn’t suffer the problems associated with greens to the same extent. This colour space is now highly favored by users of the 6-colour consumer inkjet printers such as those supplied by Epson.

Remember to use the "Save" button after you create this profile (this will ensure that it is retained for future use). You can give the profile any name you like, although I recommend BruceRGB, especially if you propose to share your files with others, since there’s a greater chance that they will be able to handle your file without conversion.

The last setting that you can make in the RGB setup dialog is – "Display Using Monitor Compensation" (DUMC). With this feature activated we are instructing Photoshop to carry out an "on-the-fly" conversion of the image data from our selected RGB "work space" to our "monitor space", using the information contained in your customised monitor profile. So now we see why it is so essential that the monitor be calibrated correctly. It should also be noted that this "on-the-fly" conversion does not impact upon, or damage the image data in any way.

If you find that your prints don't match the monitor image (i.e. to dark, to light, etc.) then try switching DUMC off. If the screen more closely matches the print with DUMC off then your monitor calibration is "broken". I recommend that you try the method I described for monitor calibration which is based upon the "Adobe Monitor Profile".

For Photoshop users who share files with others, and especially across platforms (PC to MAC and vice versa) the following should be noted.

"If you open a file that has been colour adjusted in a gamma 1.8 workspace into a gamma 2.2 workspace without conversion the resulting on screen image will appear darker and more contrasty than it would have otherwise have done. Conversely, if you originally colour corrected a file in a gamma 2.2 workspace and then open it in gamma 1.8 workspace without conversion then the image will appear flat and light."

The moral here is that unless you have very good reasons stopping you converting to your own workspace then you should always allow the colour space conversion to take place.

(ii) CMYK Setup

For the most part this dialog is of no interest to those of us who concentrate solely on an RGB workflow. That said there is one "gem" buried within the CMYK settings dialog that anyone using "Custom" printer profiles simply must take heed of, i.e. "soft proofing" your RGB printer. Unfortunately, it doesn’t appear to work too well with Epson’s new "Standard" printer profiles.

Image

Soft proofing your RGB printer is based upon a very complex procedure developed by Mark Hamburg of Adobe, my thanks to Andrew Rodney for giving us access to the Photoshop Actions that make the whole process much simpler to implement.

Image

So, rather than try to explain it myself I’ll let Andrew Rodney do it for me: -

"Photoshop 5 has no RGB soft proof (unlike the CMYK Preview/Soft Proof feature). That means that while having a calibrated display is VERY important, you are not looking at your RGB file with an output simulation. There IS a way to trick Photoshop into providing a soft proof for RGB files and you will generally see a much closer screen to print match. This is mostly affecting out of gamut (very saturated) colours. The process of converting an RGB output file into a CMYK profile for soft proofing is long and complex. However, you can find a PDF with the recipe and a Photoshop action on my Web page:-

(http://www.digitaldog.net/tips.html)

that allows you to load into the CMYK setup, a modified RGB profile for your printer and then use the CMYK preview (Ctrl+Y) to redraw the screen to get a closer match. Of course the quality of all this depends on the quality of the output profile and how well your display really is profiled and calibrated."

(iii) Grayscale Setup

This dialog allows us to define our grayscale working space by stating whether it is based on RGB neutral values (i.e. equal values of Red, Green and Blue) or simply based on Black ink. If the latter is chosen then the dot gain curves defined in the CMYK dialog are used. Remember to switch "Off" RGB soft proofing feature described above if you are using that feature.

Image

If you are using a "Custom" printer profile there is a lot of merit in converting your grayscale images back to RGB before outputting to the printer. Although, it is worth trying both options, and settling one you prefer rather than blindly following convention or even my suggestions.

(iv) Profile Setup

I’ve heard it said that unless you share your image files with other users or have been using an earlier version of Photoshop then the Profile Setup feature is surplus to requirements, nothing could be further from the truth.

The Profile Setup dialog is in fact fundamental to determining how (or even whether) Photoshop acts upon images when they are "opened" or "saved". If you set the various options incorrectly you could potentially destroy an image and never even know that you’ve done so.

It performs two functions, namely:-

 

> It offers you a method of ensuring that images get converted into your working space, and

> It lets you embed an ICC profile (or "tag") within the file that describes the workspace in which the image was created.

As can be seen from the screen-grab below, the dialog is separated into three distinct sections, "Embed Profiles", "Assumed Profiles", and "Profile Mismatch Handling".

The Embed profiles section is fairly straightforward in that by checking the boxes we are effectively telling Photoshop to automatically embed our workspace profile within the file when we save the image. By default all the checkboxes are normally "On". It is recommended that you leave this section of the Profile Setup in its default state, the exception being when you open a printer calibration Test target (typically those used with Device Profiling Packages such as WiziWYG, EZcolor, etc.). With calibration targets it essential that you don’t allow the image to be saved (usually by accident) with your work space profile, so its better to be safe than sorry, with printer calibration images make sure "Embed Profiles" is "Off". However, remember to set it to "On" again once you finish with the printer calibration.

The settings you see in the screen-grab below are generally accepted as the safest choices (although not necessarily the defaults that you will obtain when you first install Photoshop, so please check), and will enable you to avoid virtually all image data damaging scenarios that you may encounter when opening files from whatever source. One interesting point about Embed Profiles and certainly one to keep in mind. If you deselect the option then Photoshop (so far as I know no other program does this) WILL embed a profile, but this profile will be a special profile indicating to Photoshop that the user made this choice. When you open such an image you will NOT get any warning messages, etc., this is quite deliberate and also a good thing.

Image

The "Assumed Profile" section is where we tell Photoshop how it should deal with images that contain no embedded profile.  It doesn’t actually do very much other than flag up the "Missing Profile" dialog as shown below, and even this only happens when you open an actual image. Of course if we have set the "Profile Mismatch Handling" section to something other than "Ask When Opening", it will totally ignore the fact that the file has no embedded profile and open the image in a colour space previously specified by you in the "Assumed Profile" RGB pop-up window. So it is important that you ALSO adhere to the following advice on "Profile Mismatch Handling". You should consider the "Missing Profile" and "Profile Mismatch Handling" sections as "safety nets", they're designed to slow you up and make you think.

In the example below the image contains no embedded profile, if you don't know the source then select "Don't Convert". If you do know the source then make that the selection in the "From" pop-down window then choose "Convert". Typically an image scanned outside of Photoshop will cause this dialog to appear. If the appearance of the image changes drastically in colour or density you made the wrong choice, you can use Photoshop "History" to get you back to original image.

Image

Example - opening an image with "no" embedded profile

The final section of the Profile Setup dialog is the "Profile Mismatch Handling" section. Get the settings in this section wrong and, your image data is very likely to end up in a less than optimal state. For each of the three pop-up windows we have three choices, "Ignore", "Ask When Opening", and "Convert".

Taking each of the options in turn:

  • "Ignore" – This option simply opens the image in your current RGB, CMYK or Grayscale workspace without any conversion of the image data. At first this may appear to be a perfectly reasonable choice, but note, by not allowing a colour space conversion we are in fact changing the "Colorimetric" meaning of the image data thus it will appear on your monitor and print differently from what it would have done on the system in which it was created.

  • "Ask When Opening" – With this option, if you open an image that has the no profile embedded within it, you will be presented with dialog similar to that shown above. If the file has an embedded profile, but it's the wrong profile, then you will get the dialog shown below. It will be displayed in the "From" pop-up window. The "To" pop-down window will usually be "YOUR" actual Photoshop "RGB", "CMYK", or "Grayscale" colour space depending upon which mode, etc. you are currently working.

  • "Convert to ----- C" – This is the most dangerous option in that it allows Photoshop to automatically convert the file you are opening "From" and "To" the colour spaces you specified in the "Assumed Profiles" section. For most this is not the best option for very obvious reasons (e.g. a calibration image will automatically be converted into your current work space thus destroying it).

Image

Example - opening an image with the "wrong" embedded profile

The example above shows that the embedded profile within the image is "Adobe RGB (1998)", since the Profile Mismatch dialog appeared we must make one of two assumptions depending on the workspace you're actually working in.

1. You are using a colour space other than  "Adobe RGB (1998)", e.g. ColorMatch, sRGB, etc.

2. The profile is NOT what it claims to be. This actually occurred with the original Nikon version of BruceRGB, so don't dismiss it as a possibility.

If the dialog appears, and unless you have very good reason to do otherwise it is recommended that you leave the Engine: at "Built-in", Intent: at "Perceptual Images", and "Black Point Compensation" at "On" at all times.

Remember, the "Missing Profile" and "Profile Mismatch" dialog boxes are designed to WARN you that something is amiss, they will only appear when you open an actual image, and not when you are configuring  "Profile Setup".

5. Profile-to-Profile

Although not specifically part of the Color Settings menu, "Profile-to-Profile" (P-to-P) does form an essential part of the colour management system, and is found under the Image/Mode menu. Profile-to-Profile is a very powerful tool in that it effectively lets you convert an image between any two colour spaces, as and when required. However, there is also a "Health Warning" that needs to be considered – "Photoshop does not keep track of any colour space conversions undertaken by P-to-P", which means that the user could potentially save an image with the wrong colour space profile (tag) embedded within it (remember, that unless you specify otherwise the profile saved with an image will be that of your current Photoshop work space).

Image

The "From" pop-up is where we select the "Source" colour space and the "To" pop-up the "Target" colour space.

It is also generally recommended that in Profile-to-Profile mode you specify the specific "To" and "From" colour spaces (e.g. From: LS2000Scanner - To: Adobe RGB (98) rather than From: LS2000Scanner - To: RGB), even if Adobe RGB (98) is the colour space you have chosen in the RGB setup dialog as your normal workspace.

Note: It is normally best to keep "Black Point Compensation" Unchecked when converting from scanner profiles.

  • For a more comprehensive explanation on scanning workflow see Bruce Fraser's Article at:-

http://macworld.zdnet.com/1999/09/create/fraser.html

  • For a comprehensive explanation on what each of the colour management "Engines" and render "Intents" actually do, please refer to Andrew Rodney’s Tips page at:-

http://www.digitaldog.net/tips.html

Profile-to-Profile has three main functions:

  • As a time saver, whereby we find, that having opened a file without colour space conversion we realise that we should have done so. By using P-to-P we can avoid closing the file, shutting down and restarting Photoshop.

  • We can also use it to convert between the native colour space of our input devices (e.g. scanners) and our current workspace. I mentioned earlier that some scanner manufacturers (e.g. Nikon LS2000 and LS 30 film scanners) allow you to scan images in the devices native and usually very wide colour space. The problem is that Photoshop has no idea what colour space the image is in because there is no embedded profile, and worse still no equivalent to "Profile Mismatch" or "Missing Profile" for images imported via Acquire mode (i.e. "Twain" or "Plug-in" modules). So in this situation we must force the colour space conversion ourselves.

  • You should also note that quite often a P-to-P using the devices "Native" or even "Customised" profiles could result in quite dramatic shifts in colour, hue and saturation. This usually occurs if you have made colour and gamma adjustments within the scanner software. Remember, if you propose to use device profiles within your scanning workflow then you must never make colour adjustments within the scanner software. Remember also that, what you see in the scanner Preview window is based on your "monitor space" and bears no resemblance to the actual colours, etc seen by the scanner. So if you carry out your colour adjustments within the scanner software I recommend you use your monitor profile in the "From" pop-up window of the P-to-P dialog and not the scanner profile, be warned!

Note:  The one rider to my previous statement regarding the need to use P-to-P when scanning into Photoshop is if you use software such as LaserSoft's SilverFast, or on your scanner software is designed specifically to integrate with the Photoshop CMS, which is unfortunately still a very rare occurrence, NikonScan 2.5x being an exception. When configured correctly such software will allow wysiwyg previews.

  • The final use of P-to-P mode is for preparation of print files for output the RGB printers or film recorders whose drivers do not contain any form of colour management or were we chose to switch it off deliberately. A typical example of the latter would be when using "Customised" printer profiles.

6. Colour Wheel and Colour Correction

Again, whilst not strictly speaking part of colour management I have decided to include some basic information on the subject of colour correction techniques. These are not unique to Photoshop; in fact much of my colour theory has been gleaned over a period of twenty years printing Cibachrome prints in a conventional darkroom.

During those years it has never ceased to amaze me, how some supposedly intelligent individuals just came apart (mentally) at the thought of even trying to identify and correct a colourcast. So before I begin here’s what I consider to be one of the best presentations of the RGB/CMYK colour wheel that I have yet to come across. This diagram has been copied from a book (classified by me as a must have book) entitled Photoshop 5 Artistry, by Barry Haynes and Wendy Crumpler. I know it’s a breach of copyright, but just think of the free advert I’ve just given them .

RGB to CMYK Colour Relationships

Remember the significance of both colour spaces; RGB is what we see on our monitor and CMYK are the inks used to create the various colours in print.

Before we look at the diagram in use let’s deal with another issue that seems to cause confusion – the term "complements". As the diagram shows:-

  • Red is the complement of Cyan, so Cyan filters out Red Light;

  • Green is the complement of Magenta, so Magenta filters out Green Light; and

  • Blue is the complement of Yellow, so Yellow filters out  Blue Light

What does this mean?, simple; by reducing "red" we’re actually adding "cyan". By increasing "magenta" we’re reducing "green", and so on.

So what makes the above version of the colour wheel so good? Well just look at the relationships between RGB and CMY and how they are specified.

Most of us (me included) appear to have some difficulty in specifying a cast in one of the CMY colours but virtually none when it comes to specifying a cast if it’s "red", "green" or "blue" biased. So in this context I will let you decide how to interpret the diagram yourself, but remember we all make mistakes, and its only through finding the appropriate correction through trial and error that we will ever learn the true art of colour correction. One "Tip" though, it is always preferable to make colour adjustments that effect one colour rather than two, think about it!

At least with this diagram there’s a better chance that we can quickly establish the most appropriate correction. I hope it makes the task of determining the bias of a colourcast all the more easier for you in the future, so please feel free to Print the diagram and pin it to your workroom wall for reference.

When it comes to actual colour correction inside Photoshop I think most novices find the "Variations" or "Color Balance" dialogs to be the easiest to get to grips with. However, they don’t really provide you the level of control required to make accurate colour adjustments. On many occasions you will find that the colour cast in say the shadow region is one colour and the cast in the highlight another colour. The best option for colour correction in that situation is to use the "Curves" tool, I know it’s a complicated tool to use, but the sooner you learn to use it, the sooner you will produce top flight colour corrected images. You may also find some benefits to be in using the "Selective Color" controls. I have found two books of particular benefit when trying to perfect the art of colour correction; i.e.;

    • Real world Photoshop 5, by David Blatner and Bruce Fraser, and

    • Photoshop 5 Artistry, by Barry Haynes and Wendy Crumpler

Both books offer a wide range of advice on all things Photoshop and should form a good foundation upon which you can further develop your knowledge in its use.

Adobe Community Professional

 

 
Footer
Contents on this site: Ian Lyons © 1999 - 2018. All Rights Reserved