Colour depth, also known as bit depth or pixel
depth, refers to the number of bits used to indicate the colour of a single
pixel on a monitor.
When referring to a colour component, the colour
depth concept is also referred to as bits per colour (bcp), bits per channel
(bpc) and bits per sample (bps).
It’s worth noting that for example 16 bit can
mean 16 bits per pixel or 16 bits per channel. 16 bits per pixel come up to
65,536 colours while 16 bits per channel mean 281,474,976,710,656 colours.
This is different to the Gamut as that refers to
a range of colours. While colour depth is precise, expressing the level quality
of colour.
The greater the amount of bits per pixel, the
greater the variety and quality of the images displayed. In turn the less bits per pixel the lower the
quality and variety.
The very first monitors and graphics cards found
in the Apple Macintosh for example only supported 1-bit colour. This was
monochrome, but Black and white was most common.
That was back then, now thanks to advancements
in technology computers support at the very least 32-bit colour. Meaning 32 bit
colour is capable of displaying 16,777,216 colours (2 to the 34th power) plus
alpha channel used for transparency (4,294,967,296 colour combinations). Transparency
needs to be sent to the display, as displays are opaque.
Windows 7 can now support 48-bit, allowing
281,474,976,710,656 colours to be displayed. 48 bit will only work if the video
card supports it.
Bellow are all the colour depths in use from the
first to the most recent.
- 1-bit (21 or 2 colors) - Monochrome
displays.
- 2-bit (22 or 4 colors) - CGA displays.
- 4-bit (24 or 16 colors) - EGA displays.
- 8-bit (28 or 256 colors) - VGA displays.
- 16-bit (216 or 65,536 colors) - XGA displays.
- 24-bit (224 or 16,777,216 colors) - SVGA
displays.
- 32-bit (16,777,216 colors + Alpha channel (232 or
4,294,967,296 color combinations))
- 48-bit (248 or 281,474,976,710,656
colors)digital
1-bit
2-bit
4-bit
8-bit
24-bit (true colour)
For the high quality image to be viewed at its
full potential the source, connection, display and media also must be of the
highest quality. As files with high colour depth are very large and require a lot
of processing power. They are mostly compressed highly, which negatively
effects colour fidelity.
Websites such as Youtube and Netflix serve
highly compressed video also, even television. This is done to save on
bandwidth and infrastructure costs resulting in much of the detail being lost.
This is not much of a problem when there are
many vibrant and varied colours but creates a non-detailed, block-like image
when dark scenes occur with similar colours near each other. Shadows are the
best way to recognize noticeable differences in quality.
Bellow are 3 scenes from the same animation.
The first image is a varied and vibrantly coloured scene and the second and third are scenes in the shadows with dark colours.
To make the most out of 48-bit and even 32 bit
you must not only have the right set up but also get content from the right
places with higher quality codecs and encoded at a high bit-rate.