Do Grayscale Images Take Less Space?
Grayscale images usually take less space than those represented in the more common sRGB space. However, subsampling and optimizations applied on chroma (colors) channels can be so aggressive (without visual impact) that a 4:2:0-subsampled image is sometimes pretty close to a grayscale image in terms of size.
Some formats like JPEG/JFIF allow saving images represented in a grayscale space, i.e., with each pixel encoded as a single 8-bit value from 0 (black, full dark) to 255 (white, full bright). For color images, common formats like JPEG generally represent images in the sRGB space, i.e., with each pixel encoded as a 3×8-bit triple (24 bits per pixel total). (we assume we are not talking about HDR images here.)
Question: Thus, can we save space using grayscale (8 bpp) instead of sRGB (24 bpp)? Let's see with a B&W image. (original output is B&W.)
In fact, sRGB is not how internal pixels are formatted. It's how the raw input (to be encoded) and the raw output (decoded) must be represented.
