save image to be used as array 8 bit

Forum|Forum|4 years ago
November 16, 2021
2 replies
431 views

Hi there,

I have to save 8 bit images with the following structure when converted to an array:

array([[[ 60, 124, 150, 255],
        [ 60, 124, 150, 255],
        [ 60, 124, 150, 255],
        ...,

But when I save as png 8 bit I obtain

array([[[115, 124,  67],
        [118, 127,  70],
        [122, 131,  76],
        ...,

Thank you!

macOS

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Brainiac

I have no idea how you are going from Photoshop to PNG to this array data, but that is not the form used by PNG. In particular, PNG-8 does not contain a 2D array of RGB or RGBA values, one per pixel; that would be impossible, since you have only 8 bits per pixel. Rather it stores a 2D array of indexes. Each index looks up an RGB value (not RGBA). A PNG-8 file may additionally include a tRNS chunk, which gives transparency values for specific index values.