Lately I am keeping myself busy with a very delicate photo assignment for the graphic design agency I work for here in Calgary. I am photographing a whole lot of art work to use in an upcoming art book. The art is ranging from your simplest paintings, to complicated 3D video installations.
It was on one of those installations that I encountered a very peculiar issue with Photoshop's photomerge. You know the tool you use to create multiframe panorama's.
I was using this tool to create a panoramic of a 20 foot wide video install when my eye caught something strange. After some googling I could not find anyone on the "world wide intrawebs" mentioning anything about this issue. This is why I writing this in the hopes of getting an answer.
While merging 3 horizontal shots, my eye caught these strange patterns. I encourage you to click open these files so you have a clear understanding what is going on. Look at the black portion of the 100% screencap.
OK so this might be hard to see on your monitor. But I am working in a pitch black space with only the light from my monitor and this projection. So these minute imperfections POP off the screen. I photoshoped this screencap to show the patterns more clearly (again click it open to see it larger).
See it now? This was added to my photo's using the auto function in Photoshop's photomerge and clicking all 3 check boxes on (just like in this screenshot).
My guess is that Photoshop need to adds these patterns to fix for the perspective distortion in your photo's that you are merging. It add's just a little bit of data to your pixels. But of course that little bit of extra data shows up in the pure blacks.
Every blending technique has it's own pattern actually. Here's another one. Using the Perspective technique with only the first boxed checked on.
Or what about this one. Perspective blending technique but this time with ALL 3 check boxes clicked on. Look at this!
I suggest you can try this out for yourself. But my guess is is that every blending technique has it's own pattern. Well that is what my investigation tells me.
O and here is the kicker.
It ONLY happens on 16 bit images. If you use 8 bit images, you are totally fine.
Interesting huh?
Adobe, please fix this! This is clearly a bug that nobody noticed!
I have noticed this in dark areas of certain photos but always assumed that it was something to do with the sensor in my older Canon 30D (have not seen it yet on the 7D). Have noticed this on a number of images but none were stitched or blended. I thought it was just me!
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