interpretation of imread output array values

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Timothy Dunning
Timothy Dunning 2023-2-22
编辑： DGM 2023-2-22
hi, I'm trying to use imread to get an array representation of an image, then search that array for places where a specific colour occurs. I can't seem to find any doumentation on how the double, presented in the array, represents the colour at that location. How do I know which number represents which colour so that i can search for it?
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Stephen23
Stephen23 2023-2-22
"True, but imread() doesn't support indexed images in JPG or JP2."
Could you please show a reference to indexed JPG and JP2 image formats.
https://en.wikipedia.org/wiki/Indexed_color#Image_file_formats_supporting_indexed_color
I do not see how spatial image compression using frequencies/wavelets could be indexed.
DGM
DGM 2023-2-22
编辑：DGM 2023-2-22
It doesn't make sense to me either, and likewise, I can't find any mention of such a thing existing
... except the statement from the webdocs:
Indexed JPEG 2000 images are not supported. Only JP2 compatible color spaces are supported for JP2/JPX files. By default, all image channels are returned in the order they are stored in the file.
Which seems to suggest that maybe there exist some non-compliant files that are indexed. I don't know why else they'd point out that imread() can't read such a thing.
Even if this is all just a poorly-worded comment about being incompatible with things that don't exist, I tried to to phrase my original statement to be safe either way.

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Timothy Dunning
Timothy Dunning 2023-2-22
The file is an RGB .jpg and it produces a 3D array where each value is a uint8 in the range 0-255 representing the rgb colour scale. Thanks for the help.

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