Last Sync: 2022-10-10 13:00:05

Hardware/Binary/Image_and_colour_encoding.md

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 ---
-title: Image encoding
+title: Image and colour encoding
 categories:
   - Computer Architecture
 tags: [binary, binary-encoding]
 ---
+
+# Image encoding
+
+## Binary encoding of colours
+
+The approach to encoding binary representations of colour is very similar to the approach we explored when looking at the encoding of [alphanumeric values](/Hardware/Binary/Text_encoding.md).
+
+We begin by determining the total number of colours and colour shades we want to represent. With this value established we then decide on the bit-length required that will accomodate this number of variations. Finally, we assign a binary number to each representation.
+
+### Greyscale
+
+We can start with a limited palette: greyscale. Here there is black and white and number of interim shades of grey. The convention is to use an 8-bit number which, given $2^8 = 256$ provides 256 shade variations.
+
+In decimal, 0 is equal to black (zero light intensity) and 255 is equal to white (full light intensity). Some examples of this (including binary and hex representations are below):
+
+![](/img/greyscale-encoding.svg)
+
+### Colour encoding
+
+A single 8-bit number is sufficient for 256 greyscale combinations but with colour, the convention is to use three 8-bit numbers where each byte corresponds to a value for red, green and blue (RGB). Thus the overall bit-length is 24 ($2^3 + 2^3 + 2^3$). Each value corresponds to a light intensity for the given colour. Combined they are capable of representing all colours.
+
+Some examples below
+
+#### Red
+
+Red is represented in RGB with all 8 red bits to set to 1 and the remaining 16 bits for the other two colours set to 0.
+
+![](/img/red-encoding.svg)
+
+#### Yellow
+
+Yellow is represented in RGB with both red and blue set to 1 and the remaining 8 green bits set to ):
+
+![](/img/yellow-encoding.svg)
+
+## Binary encoding of images