Computer colour conversion

There are many web pages that describe 8 bit 'browser-safe' colours but it is not so easy to find a page which describes how computers convert from 24 bit to 16 bit colour.

The 24 bits consist of three groups of 8 bits. The groups define red (R), green (G) and blue (B). These eight bits are often converted to five bits. Although this appears to only use 15 bits the extra bit is used to provide extra greys. The colour chart below contains all variations of R with both G and B set to 'ff'. By adjusting a computer to 16 bit colour and using a colour meter, such as Apple's 'DigitalColor Meter', the colour chart can be examined to determine which colour the computer displays for each cell.

This has been done this using Netscape 4.76 on an iMac with Mac OS 9.1. The results are tabulated to the right of the colour chart.

Colour chart for xxffff Conversion
000102030405060708090a0b0c0d0e0f
101112131415161718191a1b1c1d1e1f
202122232425262728292a2b2c2d2e2f
303132333435363738393a3b3c3d3e3f
404142434445464748494a4b4c4d4e4f
505152535455565758595a5b5c5d5e5f
606162636465666768696a6b6c6d6e6f
707172737475767778797a7b7c7d7e7f
808182838485868788898a8b8c8d8e8f
909192939495969798999a9b9c9d9e9f
a0a1a2a3a4a5a6a7a8a9aaabacadaeaf
b0b1b2b3b4b5b6b7b8b9babbbcbdbebf
c0c1c2c3c4c5c6c7c8c9cacbcccdcecf
d0d1d2d3d4d5d6d7d8d9dadbdcdddedf
e0e1e2e3e4e5e6e7e8e9eaebecedeeef
f0f1f2f3f4f5f6f7f8f9fafbfcfdfeff
 
 24 bit   16 bit

00 to 07    00  
08 to 0f    08  
10 to 17    10  
18 to 1f    18  
20 to 27    21  
28 to 2f    29  
30 to 37    31  
38 to 3f    39  
40 to 47    42  
48 to 4f    4a  
50 to 57    52  
58 to 5f    5a  
60 to 67    63  
68 to 6f    66  
70 to 7f    73  
78 to 7f    76  
80 to 87    84  
88 to 8f    8c  
90 to 97    94  
98 to 9f    9c  
a0 to a7    a5  
a8 to af    ad  
b0 to b7    b5  
b8 to bf    bd  
c0 to c7    c6  
c8 to cf    ce  
d0 to d7    d6  
d8 to df    de  
e0 to e7    e7  
e8 to ef    ef  
f0 to f7    f7  
f8 to ff    ff

This page will be extended with a grey chart and a 16 bit to 8 bit conversion table - please return later.

Links:





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07 - 06 - 2020