Colour Depth

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.