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When analyzing my BMP image, I found that there are three fields in my resolution, ex. 960 x 540 x 32. Why is this happening?

I have a BMP file I am trying to run steganography software on. While trying to run, the software tells me that the bmp file's format is not accepted. I looked into it and ran file on the image and got this:

output.bmp: PC bitmap, Windows 98/2000 and newer format, 960 x 540 x 32, cbSize 2073738, bits offset 138

As you can see, there are three fields in the resolution. Can anyone tell me why this is happening?

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The three fields in the BMP image's resolution stand for its width, height, and colour depth (the number of bits used to represent the colour information of each pixel).

The BMP image in this instance has a resolution of 960 x 540 x 32, or 960 pixels on the wide side, 540 pixels on the tall side, and 32 bits per pixel for the colour depth.

The colour depth of the image might not be compatible because the steganography software in use has specific requirements for the BMP file format.

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    Might be worth explaining to the OP explicitly what the 32 bits represent, i.e. 8 bits each for the RGB channels and 8 bits unused (as the BMP format doesn't support an alpha channel).
    – Michael MacAskill
    Mar 19 at 7:42
  • @MichaelMacAskill BMP format can support an alpha channel with a 32bpp depth and even a color depth of 64bpp.
    – Lorenzo Donati support Ukraine
    Mar 19 at 12:27

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