In this blog, I will be explaining about ‘Bit Depth‘ or ‘Bit’, from basics all the way up to practical stuff. My name is Lalit M S Adhikari and we are at LTY. Let’s dive into our topic!
Table of Contents
What is Bit
The word ‘Bit’ came from two words, ‘Binary’ and ‘Digit’. Binary system works only with ‘Two’ values either ‘0’ or ‘1’.
What is Bit Depth
Bit Depth specifies, ‘how much color (tonal) information is available for each pixel in an image’ or ‘color information stored in an image’.
More Bits of information per pixel, result in more available colors and more accurate color representation of an image, thereby also affecting the size of image.
It does not mean that the image necessarily uses all of these colors but that it can instead specify colors with that level of precision.
The simplest image, 1 Bit image, can only show two colors, black and white.
Bit Depth is also known as Color Depth.
When referring to a pixel, the concept can be defined as bits per pixel (bpp).
When referring to a color component, the concept can be defined as bits per component, bits per channel, bits per color (all three abbreviated bpc) and also bits per pixel component, bits per color channel or bits per sample (bps).
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Bit Depth & Number of Colors
Most of Graphic software, by default, work on 8 Bit per color channel, providing two options for Color Modes (RGB & CMYK) and default value for Color Profile as per your choice of Color Mode.
A 8 Bit document generally means 8 Bits of color information per color component or color channel. If we consider a RGB document then 8 Bits of information for Red, 8 Bits of information for Green and 8 Bits of information for Blue. Hence, it’s also called as 24 bit image.
8 Bit = 256 colors per color component
16 Bit = 65,536 colors per color component
32 Bit = 4,294,967,296 colors per color component
Bit depth matters in post-production.
When we have to make large prints or create HDR photography or care to preserve great range of tonal values, it is wise to work on our images in a 16 bit mode, which gives us greater tonality and color values.
Try to work in 16-bit mode for as long as possible.
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How to calculate number of Colors with Bit
A single Bit has 2 possible values, 0 or 1.
When you combine 2 Bits then you can have four possible values (00, 01, 10, and 11).
When you combine 3 Bits, you can have eight possible values (000, 001, 010, 011, 100, 101, 110, and 111). And so on.
In general, the number of possible choices are 2 raised to the number of bits. So, the simple formula is
Total tonal values = 2n
where, n = number of bits & 2 came from the total values possible for a single bit.
Depending on the quality of your monitor, you can probably only display differences up to 8-10 bits.
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RGB Color Mode & Bit
I have chosen RGB, being the most popular and used Color Mode, to show the relationship between Color Modes and Bit.
We already that RGB has three color channels, namely, Red, Green and Blue. By default all Graphic Software work in 8 Bit document setting.
As discussed above 8 Bit will represent 8 Bit of color information in each color channel present in the Color Mode. Hence, each pixel will have 24 Bit of color information.
So, as we already know
8 Bit = 28 = 256 colors per color channel
Hence, Red channel color value = 28 = 256 values of Red,
Green channel color value = 28 = 256 values of Green
Blue channel color value = 28 = 256 values of Blue
These are the values per color channel. To calculate the total color possibilities for a RGB, 8 Bit document, we have multiply these values together.
As Colors in RGB Color Mode are formed as a result of combining these three color components.
Total Color Possibilities = (Total color values of Red) x (Total color values of Green) x (Total color values of Blue)
= 256 x 256 x 256
= 16,777,216
In Graphic software (like Photoshop, illustrator etc.), the 256 individual color value is represented as integers 0-255 (internally, this is binary 00000000-11111111 to the computer).
8 Bit (24 Bits per pixel)
As we have have calculated earlier, 8 Bit images have more than 16.7 million color possibilities.
The human eye can distinguish about 10 million different colors. Hence, an 8 Bit image has more color possibilities than what a human eye can distinguish.
That’s why the maximum number of images we came across are 8 Bit images.
Most of our display devices are also 8 Bit or True Color displays. Also this is the reason why most of the final output for productions are converted 8 Bit.
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16 Bit
A real 16 Bit RGB document have 281,474,976,710,656 color possibilities. That’s a tremendous amount of colors.
As you can see this could be huge to deal with even at current computation level. That’s why even Photoshop doesn’t offer us true 16 Bit.
Photoshop offers us 15+1 Bit which calculates as
215+1 = 32769 possible values per channel.
Here’s Adobe Community Thread regarding this topic.
In fact, all the DSLRs available also doesn’t offer true 16 Bit. They are somewhere between 12-14 Bit.
Support for 16 Bit images in Photoshop
Photoshop provides the following support:
- Work in Grayscale, RGB Color, CMYK Color, Lab Color and Multichannel modes.
- Use all tools in the toolbox except the Art History Brush tool with 16 Bits/Channel images.
- Apply color and tonal adjustment commands.
- Work with layers including adjustment layers.
- Apply numerous Photoshop filters.
- To take advantage of certain Photoshop features, such as some filters, you can convert a 16 Bit image to an 8 Bit image. It’s best to do a ‘Save As’ and convert a copy of the image file so the original file retains the full 16 Bit image data.
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8 Bit Vs. 16 Bit
| 8 Bit | 16 Bit |
|---|---|
| They have more than 16 Million colors. | They have more than 281 Trillion colors (in pure form). |
| They have smaller file size. | They have larger file size. |
| They are common for most of images. | They serve a special purpose and not commonly used. |
| It is advised to convert all production works to 8 Bit. | It is advised to do all the editing in 16 Bit. |
| Low tonal variations. | High tonal variations. |
32 Bit
32 Bit in pure form supports the most number of tonal variations. Due to which they have file sizes greater than a 16 Bit.
Hence, use a lot of physical memory and time to process.
Bit Depth Vs. Color Space
Bit Depth determines the number of possible tonal values where as Color Space or Color Profile determines the maximum value that will be available.
For Example: Let’s say we have a pack of Crayons. Now here, Bit Depth will determine the number of crayons where as Color Space will determine the limit of most saturated color available regardless of the number of crayons.
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How many Bits can we see
For human any images between 8 Bits per channel to 12 Bits per channel is the limit in case of a standard display.
If you are using a High-end display then 10 Bits per channel to 14 Bits per channel will be the limit.
Why to use Bits more than what we can see
Using more Bits than what we can see is always recommended for editing an image.
As editing process is much likely to destroy some of the color variations preserved in the image.
Hence, is better to work in a large Bit Depth.
How many Bit should we use in Photoshop
Use 8 Bit for most of common tasks like creating a Social Media Post, poster for digital purpose etc.
Use 16 Bit for color grading, color correction, manipulations, matte paintings and printing stuff.
How to change Bit preferences in Photoshop
You can either create a document with your preferred Bit by changing the following option in New Document Dialog box in Photoshop:
Or you can change it after creating a document or opening an image. By simply going to Image menu then Mode and then chosing your preferred Bit.
How many Bit do we need for Internet
We need 8 Bits per Channel for Internet.
How many Bits do we need for printing
In case for printing, if your printer accepts 16 Bit, always go for 16 Bit otherwise 8 Bit is fine.
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- Presets in Photoshop
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Keep this going please, great job!
Thank you!
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