Understanding bit depth in photography

Bit depth defines the number of unique colors that are available in an image’s color palette using binary representation. This means the maximum numbers of colors  you can describe using “0” and “1”.

In fact, every pixel’s color in an image or on a monitor can be obtained combining the three primary colors: red, green, blue. Because of that, each color is often referred as a color channel and can have a range of intensities. Each color’s intensity is specified by its bit depth. This bit depth for each primary color is termed as “bits per channel”. The term “bits per pixel” or “bpp” refers to the sum of all three color channels or the total number of colors available at each pixel.

How analog is converted in digital?

We live in an analogue world. Furthermore our devices don’t know how to interpret the surrounding world. Therefore for a camera the light is converted into predefined levels. The camera produces an with 8 bits / channel. This translate in a total of eight ‘0’ and ‘1’. Consequently if we do the math properly this allows us 2 to the 8th values. This means 256 different light intensity levels for each primary color. So, we know that we have 3 channels for each pixel. If we multiply all three channel then we obtain 256x256x256 = 16,777,216 different colors. Yes, you read it correctly, 16 million possible colors. This is referred as 24 bits per pixel which is composed of 8 bits per channel.

Bits per pixelDigital representationNumber of colors availableCommon name(s)
1'0' or '1'2Monochrome
2'00' to '11'4CGA
4'0000' to '1111'16EGA
8'0000 0000' to '1111 1111'256VGA
16'0000 0000 0000
0000' to '1111 1111 1111 1111'
65,536XGA, High Color
2416,777,216SVGA, True Color
3216,777,216+Alpha (transparency)
48281 Trillion

Visualization

To be much easier to visualize all the mathematical stuff you were reading so far lets visualize it. Therefore below you can find 5 different images with different bit depths. Therefore the images have a bit depth starting from 8 bits, 12, 12, 16 and 24 bits.

Bit depth visualization

8 bit

8 bit

10 bit

10 bit

12 bit

12 bit

16 bit

16 bit

24 bit

24 bit

In my opinion one image means more than a thousand words. Therefore I hope that the images speak for themselves. So you can see that the difference between 24 and 16 bits are subtle. However, this will be clearly visible if you set your display to true color or higher (24 or 32 bpp).

Final thoughts

In addition, have you ever asked yourself how many colors can the human eye distinguish? While there are still debates about the maximum number of colors the human eye can distinguish, some studies state that this can be up to 10 million colors.

Tetrachromats can see colors that most people cannot — up to 100 million, estimates suggest, which is 100 times that of the average human. Most people have three cells, or receptors, in their retinas, but tetrachomats have a fourth receptor, which may be what allows for their heightened color perception. They are usually female, and it’s estimated that about 12 percent of women carry the gene for this fourth receptor.

Finally, if you want to read more about this topic here is the link where I block-quoted the information. Also I invite you to share your opinion in the comment section below. Are you tetrechromat?

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