Raw Tuesday: 5 things you need to know before shooting raw files
5. What do 8-bit, 12-bit, 14-bit and 16-bit mean when it comes to raw files?
Every image you take contains a range of tones from pure black through to pure white, and the ‘bit-depth’ simply tells you how many different values there are.
All JPEGs are 8-bit files, so they contain 256 tones, while raw images are usually 12- or 14-bit,
so contain at least 4,096 tones.
It’s generally considered that you need around 250 different tones to produce an image that appears smooth and natural, which is why the 256 tones
in an 8-bit image are considered to be enough in most situations.
The problem comes when you start to manipulate the image using Levels or Curves in Photoshop.
These commands compress or stretch an image’s tones, creating gaps in the image histogram that can cause unsightly banding or ‘posterisation’ in the finished image.
Using Curves or Levels on an 8-bit image can lead to a loss of tones, visible as gaps in the histogram display
The greater tonal information of a 16-bit image means that you get a better quality result using the same adjustments
This is particularly noticeable in areas of smooth tones such as a blue sky, where the steps between the different tones can become visible.
With a raw file you start with many more tones, which allows you to make more extreme adjustments without these problems occurring (find out how far you can push a raw file).
can’t edit 12- or 14-bit files, so most raw editing software gives you the option of converting the image to 8
or preferably 16-bit format.
Why more bits equal more tones
Bit depth 8-bit 12-bit 14-bit 16-bit
Tonal values 256 4,096 16,384 65,536
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on Tuesday, July 24th, 2012 at 4:00 am under Photoshop Tutorials, Tutorials.
Tags: photo editing, raw files, raw format, Raw Tuesday, shooting raw