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.

 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.

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