Bit Depth

The bit depth, defines the number of bits used to indicate the color of a single pixel, or the number of bits used for each color component of a single pixel.

For images of daily life, 8-bit is more than enough. This means that a pixel is encoded on values in the range [0, 255]. However, photographing astronomical objects is more demanding and usually requires working on images with a bit depth of at least 16-bit: i.e. in the range [0, 65535]. Even better, 32-bit precision allows the most subtle information to be retained. On this last type, the pixels are either encoded in the interval [0, 4294967295], or, as used in Siril, between the floating values [0, 1]. It is possible to find formats encoding pixels on 64-bit (in the range [0, 1], but they are rare and have a very specific use. In particular the FITS format allows this.

However, not all image file formats support 16-bit, let alone 32-bit. This must therefore be taken into account when choosing a format to work with.

16-bit image

Linear image saved in 16-bit

8-bit image

The same linear image saved in 8-bit. Almost all data have been lost