How to parse colours of each pixel and compare

Add a color fill layer and make it bright red for example (anything that will show up strongly)

Right click that layer and choose Blending options

Go to Blend if

Set the underlying layer blend if values to the combination of channel values that you want to be highlighted

Dave

I'm by no means an expert on print, but it sounds like you're talking about colors going out of gamut.

In this case, you could tackle this with a color range action.

Make 3 new actions, "Gamut Check", "isProblem", "isGood"

for the "gamut check" action:

1. Record a color range step where you select "out of gamut" as the target (bottom of the list)

2. add a conditional step (on the action panel, go to the menu, select "add conditional step")

3. set this step to "document has a selection", then play action to "isProblem", and Else Play Action to "isGood"

4. stop recording gamut check

for the isProblem action:

1. add a Stop (on the action panel, go to the menu, select "add Stop...")

2. write whatever message you want to inform your user

3. stop recording isProblem

for isGood:

1. do what you want to do in case there is no problem. Can be nothing, can be something, up to you.

To use it:

The user can now play the "Gamut Check" action and will be informed if there are problems.

You can also link this action to an event in the Events manager so it is played every single time a document is opened and the user will not have to do anything. (But will be bothered every single time a document is opened)

All the best & good luck! 🙂

Checking each pixel individually is usually not plausible (at least for images of any significant size), but I expect it should possible to utilize a workaround that ultimately uses the histogram to determine the overlap. 

What’s the point of the task?