Alpha Channel Color Report

scotcht · Post by **scotcht** » Wed May 07, 2014 9:03 pm

Hey there,
I have several .tif files that all contain alpha channels. I need to find which of them contain a particular rgb value within their alpha channel. The files that I'm working with generally have fewer than three unique rgb values within these alpha channels.
I need a script that runs through each file and generates a report. Any ideas?
st

pfaffenbichler · Post by **pfaffenbichler** » Thu May 08, 2014 6:24 am

Alpha Channels have no RGB values, they are one Channel, so basically grayscale.
In any case the Channels Histogram should work just fine for the task.

This for example alerts you of the last Channel’s Histogram.
Code: Select allalert(app.activeDocument.channels[app.activeDocument.channels.length - 1].histogram)

But are there really only three or less values?
If anti-Aliasing was involved in the creation there might be »intermediate« pixels.

scotcht · Post by **scotcht** » Fri May 09, 2014 5:07 pm

Well, technically there are 256 shades of grey in the alpha channel, represented by an rgb value. I do not use anti-alias, as i need exact locations for these representations, and no gradation. The software I'm using utilizes the alpha channel to build an infrared and radar image of an aerial image, where one grey indicates water, and another indicates soil or vegetation, and another pavement.

pfaffenbichler · Post by **pfaffenbichler** » Sat May 10, 2014 9:48 am

Have you checked out the histogram yet?
Could you please post (part of) a sample image?
in what form do you need the report?

Edit:
Well, technically there are 256 shades of grey in the alpha channel, represented by an rgb value.
That statement seems nonsensical to me, but maybe I’m off on the terminology …