Bitmap colour depth
Because a bitmap image is really just a long string of 1s and 0s (binary digits, bits), it has no idea about the concept of colour.
We could store each colour as 24 bits (or 32 bits if we need transparency).
That would allow us to store pretty much any colour, but it does mean that
images which only use a few colours would take up a lot more storage than they
need to.
To fix this, we can store a bit depth, which will tell the program reading the image how many bits each pixel’s colour takes up.
The colours represented by each number is stored in a colour map.
Example: black and white images
If we store a black and white image, there are only two possible colours each pixel can have. We can represent a black-and-white image with just 1 bit per pixel (a 0 for black and a 1 for white, for example), and so our colour depth would be one bit.
flashcards
| Question | Answer |
|---|---|
| What is a colour depth in a bitmap image? | The number of bits used to store each pixel’s colour, telling the program how many bits each pixel’s colour takes up. |
| How is the mapping from numbers to colours stored in a bitmap image? | In a colour map. |
| Why might a 24-bit colour depth be wasteful for images that use only a few colours? | Because each pixel still uses 24 bits (or 32 bits with transparency), even when fewer colours would suffice, taking up more storage than needed. |
| What colour depth is used for a black-and-white bitmap image, and why? | 1 bit per pixel, because only two colours are needed; 0 can represent black and 1 can represent white. |
| What are the two components used together to interpret a bitmap image’s colours? | The colour depth (bits per pixel) and the colour map. |