Accessing pixel colours for 2 layers

Question

Hi,
I know I'm probably missing something but I can't seem to get my head around how to access what colours individual pixels are.
I suppose I should briefly describe what I'm trying to do so here goes. I need to make a photoshop plugin for a college project. The functionality required has been provided to me in the form of an external dll which I need to call. Two of the paramaters needed to do this are linear unsigned char arrays for the entire two images which have values for each pixel dependent on their colours . The plan is to have the background layer be the image the user wants to modify and a second layer where the user indcates what they want to modify by making strokes of varying colours. As such I need to create these char arrays based on the pixel values. The background one will simply be a case of storing the colours as unsigned chars and the second one will require assigning specific numbers based on the colours.
From what I have read the ReadPixelsFromLevel(...) function seems to be my best bet, although I could be wrong there, but I'm not quite sure what to do with the destination once values have been read there.
Any insight would be appreciated as my deadline is looming ever closer and my progress has stalled somewhat.
Thanks.

Answer 1

I think your assumption was right, you just need to get different channels descriptors for ReadPixelsFromLevel function.
you can obtain them from the filterRecord->documentInfo structure.
filterRecord->documentInfo->targetCompositeChannels is your writable channel (eg. red).
if you want to read from the layer other than active, you should first get the layersDescriptor and then its channelDescriptor,
eg.  filterRecord->documentInfo->layersDescriptor->compositeChannelsList.