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.

 

 

• 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.

 

 

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.

 

 

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.

 

 

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.

 

 

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.