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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. Without the tools that follow it would be virtually impossible for the user to maintain a fully colour-managed workflow.

Assign Profile

As with Photoshop 6 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/ColorSync 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 off, then an image imported into Photoshop with NO embedded profile will be "assigned", "previewed" and subsequently "saved" in 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 we can make the necessary assignment.

It is important to note that unlike the Profile to Profile command of Photoshop 5, assigning a profile will NOT convert the image (will not change the numbers; i.e. RGB pixel values). It simply tells Photoshop the actual colour space that you wish to edit and view the image in (it changes the image appearance or meaning of the numbers).




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 Photoshop 5 Profile-to-Profile. With Profile-to-Profile we were able to define the source colour space (and probably get it wrong), in Photoshop 6 and 7 this cannot be done since the assigned profile for the image is locked. The only way that this source profile can be changed is via the Assign Profile command discussed above.




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 Colour 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.

The Profile-to-Profile method of printing an image in Photoshop 5.x, here's its equivalent!

Actually, some users prefer to use the Convert to Profile command to prepare their images for printing, much as they did with Profile-to-Profile in Photoshop 5. The advantage of this approach is that it provides a very accurate preview of how the image will print, and gives the user the ability to use (and preview) the alternative conversion options.




If you do choose this approach for printing then simply select Same as Source (direct equivalent of RGB in Photoshop 5) as the Print Space, the remainder of the settings are as described the dedicated Printer Colour Management tutorial. Of course, the printer driver must be set for No Color Adjustment mode.



Photoshop Print dialog settings required for this method of printing


Also, notice that whereas in the previous examples the Source Space was the same as the Photoshop Working Space it is now the name of the media profile you selected in Convert to Profile (e.g. Epson 1270 Premium Glossy Printer Profile).

Save As

Last but not least, the new 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 versions will look slightly different, but are functionally identical.




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. Note that 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.




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 "" and the keys words "color management" is all that is required.


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