Can image have different bits per pixel and different bit dept

Question

I have a 24-bit dept png image.

Image details

Size : 4663KB
Witdh: 1920 pixels
Height: 1080 pixels
Bit Dept: 24 bit

I calculated its bits per second using the formula bpp = Scomp / NPixels said by Pedro Miguel Moreira from https://www.researchgate.net/post/How-can-one-relate-compression-ratio-CR-with-bits-per-pixel-bpp

And I got my bpp as 18 or 17.98996914

My main question is that can I have different bits per pixel and different bit dept or is bit dept = bits per pixel.

Answer 1

Your image Bit Dept is 24 bit, this refers to the uncompressed pixels, all pixels have 24 bits each; when you talk about bpp, you are talking about the compressed image, which due to compression will take less bits, but that's an average, after compression, it might not be possible to say which few bits represents one single pixel, which next few bits represents the next single pixel, they night be encoded in a completely different way.