Apply colorsync profile - what does "preserve original color space" do?

Question

Level 2

290 points

Apply colorsync profile - what does "preserve original color space" do?

With any luck the question is set out clearly in the title.

I have a number of untagged pictures in iPhoto and I need to tag them all with an sRGB colour profile. The "Apply Colorsync profile" action is clearly the one I want. But it is unclear exactly what the "preserve original color space" option in that action does. Can anyone illuminate me?

(My intent is to assign a profile rather than match to a profile as the terminology is used by Preview or Colorsync Utility.)

MacBook Pro 2.0GHz, 2GB RAM, 120GB HDD, Mac OS X (10.4.8)

Posted on Mar 6, 2007 9:08 PM

Reply

Answer 1

JASimon Author

Level 2

290 points

Mar 13, 2007 8:36 PM in response to Community User

Sadly it is also less informative as it is very hard to see if the process is 'Applying' a profile (with its associated changing of image colour values) or just 'Assigning' a profile when the profiles in question are Camera RGB, sRGB and Generic RGB.

(While experimenting it also demonstrated the alarming ability to modify the source file rather than the one I had just copied and dropped onto the Automator action. Yikes!)

Rhetorical question: Is it too much to ask for some documentation for Automator actions?

Reply

Answer 2

Mar 7, 2007 11:00 AM in response to JASimon

Personally, I'd make a copy of a picture and try it out on that, and then compare it to the original. If there was more than one option, I'd make additional copies and try it out on them, then compare them to the originals.

I also would rename the copies before trying out each setting, according to the name of the setting I would try out. In that way I could keep track of what I wanted to do to each test copy, and afterwards know what I did as I compared them to the original.

You'd likely want to specify a different picture before each time you run the workflow (or during if you make the workflow interactive).

I think that would be much more reliable than just taking someone's word for it. 🙂

Reply

Answer 3

Mar 14, 2007 5:21 PM in response to JASimon

I tried the Automator action and compared it to the "Match to Profile" and "Assign to Profile" options in Preview's "Tool" menu. I noticed visible differences in one of the four results when compared to the original. I also used the Finder's info window to compare sizes, and then "diff" in the Terminal to confirm two of the files were the same.

In the one file I tested (a screenshot), I changed the profile from Color LCD to sRGB.

It appears using "Match to Profile" in Preview gives the same results (no difference in size or with "diff") as Preview's action "Apply ColorSync Profile to Images" without the "Preserve original color space" option. Though, the action has many more profiles to choose from. The profiles of both were changed to sRGB successfully according to the info window in Preview.

Using "Assign to Profile" in Preview gave different results than choosing "Preserve color space" in the action. Preview produced a visual difference, but the action did not. They also resulted in different sizes.

According to Preview's help file titled "Changing an image to match a ColorSync profile", assigning a profile is suppose to leave the pixels unchanged. When I tried it, I noticed a visual difference for the original. Though matching a profile will change the pixels, the images weren't visually different.

Hmm, I just realized something. I wonder if this is the answer... Seems like it. Oh, I guess I better tell you. 🙂

I just realized something when comparing the two results from the action to change the profile to sRGB. Without preserving the color space, the image's profile changes to sRGB. However, preserving the color space causes the original color space to remain. Either way, the file sizes are different from the original, though not the same as each other (i.e. all three have different file sizes).

It would seem the difference caused in the action from preserving the original color space is that the original color space is preserved. 🙂

So if you really want to have the profile embedded, don't preserve the color space. In that way, viewing the info in Preview shows the profile was changed. If you preserve the color space, the profile doesn't appear to have changed even though the file has definitely been changed. Oddly enough, the images looked the same regardless of preserving the color space, but maybe that's what is intended.

Reply

Answer 4

JASimon Author

Level 2

290 points

Mar 14, 2007 6:33 PM in response to Community User

It appears using "Match to Profile" in Preview gives the same results (no difference in size or with "diff") as Preview's action "Apply ColorSync Profile to Images" without the "Preserve original color space" option.

...

According to Preview's help file titled "Changing an image to match a ColorSync profile", assigning a profile is suppose to leave the pixels unchanged. When I tried it, I noticed a visual difference for the original. Though matching a profile will change the pixels, the images weren't visually different.

Actually, that is exactly what should be going on with an 'assign'. There should be a visible difference on screen even though the underlying pixel values don't change. With match, however, the appearance on screen won't change but the pixel values will.

Thus, from your experiments, without 'preserve original color space' checked it 'Matches' while with it checked it 'Applies' a color profile (which is a combination of match and assign). Sadly, I was looking to 'Assign' so this may not be the action for me.

Thanks for your help with the experimentation.

[Explanation of why assign should result in a visual difference: The pixel value (127,0,0) in the Color LCD space is a rather drab red. In the Adobe RGB space it is actually quite a vivid red (because Adobe RGB is much bigger color space then Color LCD). If you change the assigned profile from Color LCD to Adobe RGB without changing the pixel value it will display as a much brighter red when you assign the profile. On the other hand, if you match to Adobe RGB it will convert the pixel value to, say, (64,0,0) and tag it as Adobe RGB which will display identically on the screen.]

MacBook Pro 2.0GHz, 2GB RAM, 120GB HDD Mac OS X (10.4.8)

Reply

Answer 5

Mar 15, 2007 11:50 AM in response to JASimon

Ah, okay, I've been wondering how to think about color profiles. Thank you for the explanation, now I have a better idea of what's happening. 🙂

Reply