All digital data is made up of ‘bits’, and that includes digital images. In computing, ‘bits’ are either on or off, so there are only two possible values. But when you use them together the combinations are multiplied so you can record a much wider range of values. The number of bits used is the ‘bit depth’. This is especially relevant in photography, where you need to be able to render subtle differences in tone and color.
Here’s a table showing the number of different values for different bit depths:
|Bit depth||Number of tones||File format|
|10-bit||1024||RAW (old cameras)|
|12-bit||4096||RAW (basic cameras)|
|14-bit||16384||RAW (advanced cameras)|
|16-bit||65536||TIFF (from a RAW file)|
Most images are shot in the JPEG format for convenience. This produces small, compressed files that don’t take up too much space, can be opened and displayed on any device and yet can still display the subtle tones needed for photographs.
JPEG is an ‘8-bit’ format. This means that the three color channels used to make up the photo (red, green and blue) all use 8-bits of data. This means each color channel can record 256 different shades, and while that doesn’t sound like enough to give a smooth transition of tones, you should remember that tones in a picture are rarely composed of one channel alone. These three RGB colour channels generally work in combination to produce a much wider range of tones.
Even so, if you edit a JPEG photo to shift the color balance or change the contrast, you can start to see these tones separating visually. This can show up as digital artefacts like ‘banding’ effects or ‘posterisation’, particularly in skies or other areas of even tone.
The only way round this is to capture images with a higher bit depth, as these are far less likely to show any tonal separation, even with heavy manipulation.
And the only way to do this is by shooting RAW files instead of JPEGs. RAW files are captured at a much higher bit depth and therefore have much subtler tonal information.
Some older cameras captured 10-bit RAW files. This 2-bit advantage over JPEGs is still worth having, but is low by today’s standards. Now, even cheaper DSLRs and mirrorless cameras will capture 12-bit RAW files, which is enough to give a big step up in tonal subtlety and editing potential compared to JPEGs. More advanced cameras will capture 14-bit RAW files, which are better still. A few medium format cameras can even capture 16-bit RAW files.
Some photo editing programs will let you work with RAW files directly, but with others, including Photoshop, Affinity Photo and various plug-ins, you will need to process the RAW file into an editable image first.
You can create a JPEG, but then you’re back where you started. The only other alternative is to produce a 16-bit TIFF image. This will be a much larger file, but far better for image editing. RAW processing software produces 16-bit TIFF images by ‘upsampling’ the RAW file, whether it’s a 12-bit or a 14-bit file.