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+--- Thread: Averaging images using layers (/Thread-Averaging-images-using-layers)
Averaging images using layers - Bob - 02-27-2019
I am working on a project to measure the various components of light in a night scene and need to stack and average multiple images. I am doing this using layers in GIMP 2.10.8 and hope to reduce the opacity of each stacked layer; eg 100%, 50%, 33%, etc. However in a simple test using just two layers (Black, 0.000, at 100% opacity and above that White, 1.000 at 50% opacity) the resulting "visible layer" pixels had a value of 0.737 not the 0.500 I had expected. I am not sure what I am doing wrong but would appreciate any advice on how to stack say 10 photographic images which gives equal weight to the pixel values in each image?
RE: Averaging images using layers - Ofnuts - 02-27-2019
(02-27-2019, 09:50 AM)Bob Wrote: I am working on a project to measure the various components of light in a night scene and need to stack and average multiple images. I am doing this using layers in GIMP 2.10.8 and hope to reduce the opacity of each stacked layer; eg 100%, 50%, 33%, etc. However in a simple test using just two layers (Black, 0.000, at 100% opacity and above that White, 1.000 at 50% opacity) the resulting "visible layer" pixels had a value of 0.737 not the 0.500 I had expected. I am not sure what I am doing wrong but would appreciate any advice on how to stack say 10 photographic images which gives equal weight to the pixel values in each image?
Use "Legacy" mode (selector at end of the "Mode" selector). I believe that in "Normal" mode, Gimp 2.10 works on the linear value, while in "Legacy" mode, it work like Gim 2.8 on the gamma-corrected values.
RE: Averaging images using layers - Bob - 02-27-2019
Thank you Ofnuts. Selecting under "Precision", "Linear Light" gives me in Color Picker the very pixel values I need ...but I note the adjacent RGB (%) figures are not then correct. Presumably a bug? Big thanks for your help.
RE: Averaging images using layers - Bob - 02-27-2019
Maybe I was a bit premature in giving this the tick off. I found the exported images still use "Perceptive Gamma" pixel values even when "Linear Light" is ticked in Image / Precision or in Edit / Preferences /Gamma. Something to watch for if you are into stacking images and then using the pixel values.