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There are two kind of bitmap images Raw images are not common. Sometimes used in photography. Popular ones include(d) BMP, TIFF, RAW. Note that in fact, BMP and TIFF have compression options in their specifications.

Raw images are heavy:

About units of digital file size:

• B = byte = 8 bits
• kB = kilobyte = 1000 B
• MB = megabyte = 1000 kB
• GB = gigabyte = 1000 MB
• ...
• Kio = kibibyte = 1024 B = 2¹⁰ bytes
• Mio = mebibyte = 1024 KiB
• Gio = gibibyte = 1024 GiB
• ...

The quasi-totality of images are stored in compressed form in the mass memory (image files in HDD/SSD drives, in data segment of program codes, in data RAM when a program is running) and in raw format in the working memory (data RAM or screen memory RAM).

Mid 2010s: In full HD (1920×1080 pixels), standard color (3 octets par pixels), weights

The typical RAM memory of a modern PC is 8GB, so that is a ratio of about 1 to 1300.

Mid 1980s: The inital model of the personnal computer Atari ST had a screen resolution of 320×200 pixels in 16 colours. For 16 colours one needs 4 bits = 1/2 a byte. Hence the raw image used

The machine's RAM was 512KiB~524kB. Ratio: about 1 to 16.

2020's: 8K UHD 7680×4320 = 33 177 600 pixels. If 12 bits per channel one gets

There are two kind of compressions

Examples:

• PNG: lossless, DEFLATE algorithm
• GIF: lossless, Lempel-Ziv-Welch algorithm
• JPEG: uses Fourier transforms and only keeps most significant waves.

Bird

The image is 607×471 pixels. High quality photograph with very little noise.

Klein

A 4200x4200 pixels image with an 11 colors palette and big areas of uniform colors.