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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

Figure 18 - Customised Color Settings Configuration