What is the difference between 8 bits and 16 bits. The concept of bit depth in Photoshop
You may have heard expressions such as "8-bit" And "16-bit". When people mention bits, they are talking about how many colors are in an image file. Photoshop's color modes determine the bit depth of an image (1, 8, 16, or 32 bits). Since you will be working with these characteristics quite often (for example, when in the dialog box New you also have to choose the number of bits), it is useful to know what these numbers mean.
Bit is the smallest unit of measurement used by computers to store information. Each pixel in an image has bit depth which controls how much color information a given pixel can contain.
So bit depth image defines how much color information the given image contains. The greater the bit depth, the more colors can be displayed in the image.
Let's take a quick look at the options with different number of bits in Photoshop.
1. In color mode, pixels can only be black or white. Images in this mode are called 1-bit, because each pixel can only be one color - black or white.
2. 8-bit image can contain two values in each bit, which equals 256 possible color values. Why 256? Since each of the eight bits can contain two possible values, you get 256 combinations.
With 256 combinations for each channel in an RGB image, you can have over 16 million colors.
3. 16-bit images contain 65536 colors in one channel. They look the same as other images on the screen, but take up twice as much hard drive space. These images are very popular with photographers because the complementary colors give them more flexibility when adjusting settings. Curves And Levels, even though larger file sizes can greatly slow down the program.
In addition, not all tools and filters work with 16-bit images, but the list of tools that work with them grows with each new version of the program.
4. 32-bit images, which are referred to as High Dynamic Range (HDR) images, contain more colors than you might think. But about this will be discussed in future HDR articles.
Basically, you will be dealing with 8-bit images, but if you have a camera that takes higher bit depth images, by all means, take a day off and experiment to see if it's worth sacrificing space for the difference in quality. hard disk and editing speed.
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One of the most important parameters of a digital image in photo processing is the color depth (Color Depth), or color bit depth. Perhaps you have already met with this parameter, but not everyone attaches due importance to it. Let's figure out what it is, why it is needed and how to live with it.
Theory
Let's start, as always, with a short theoretical introduction, because a good theory gives an understanding of the processes that take place in practice. And understanding is the key to a high-quality and controlled result.
So, we are dealing with a computer, and in computers, as you know, all paths lead to binary code, or zeros and ones. But how many zeros and ones we can use to determine the color tells us the bitness of the color. To make it clearer, let's look at an example.
Below you can see a one-bit image. The colors in it are determined by only one digit, which can take the value 0 or 1, which means black and white, respectively.
Color depth - 1 bit
Now let's go one step higher, to 2-bit images. Here the color is already determined by 2 digits at once, and here are all their possible combinations: 00, 01, 10, 11. So with a 2-bit color, we already have as many as 4 possible colors.
Color depth - 2 bits
Similarly, the number of possible colors increases with each step, and in an 8-bit image there are already 256 colors. At first glance, it seems to be normal, especially since 256 colors are only for one channel, and we have 3 of them. As a result, this gives 16.7 million colors. But then you will see that this is not enough for serious processing.
16 bit color (and in fact in Photoshop it is 15 bit + 1 color) gives us 32769 colors per channel or 35 trillion colors in total. Feel the difference? For human eye it's not noticeable at all ... Until we throw a bunch of filters on our image.
What will happen?
Let's take a black and white gradient as an initial example.
To quickly and easily simulate the result of heavy processing, add 2 Levels layers with the following parameters:
Layers
And this is the result we get with different color depths of the original image:
Gradient after applying filters
As you can see, the top 8-bit gradient became clearly banded, while the 16-bit one retained a smooth transition (if you don't have a very high-quality monitor, there may be a slight banding on the lower gradient as well). This effect of losing smooth color transitions is called posterization.
In real photographs, posterization can also appear on various gradients, in particular, on the sky. Here is an example of posterization on a real image, for better visibility, the area where the effect is most noticeable is cut out.
Posterization on a photo
What to do?
Always make sure that your source images for processing are 16-bit. But keep in mind that converting an image from 8 bits to 16 will not give any useful effect, since there is no additional color information in such an image initially.
Watch the video below to learn how to convert photos from RAW to 16-bit in Adobe Camera Raw, Adobe Photoshop Lightroom, and DxO Optics Pro.
What is 16 bit and 8 bit color profile?
Photos taken with a digital camera are saved in sRGB or RAW (Adobe RGB) color space.
Each color can be represented in color format as 8 bits (jpg format) or 10 or 12 sometimes 14 bits of color per color channel (pictures taken in RAW format).
What does this mean in practice.
8 bits of color generates a total of 256 shades of the same color.
If you are already using 10 bits, then it turns out (2 to the power of 10) already 1024 shades of the same color.
If you use 12 or 14 bits per channel, you get 4096 and 16384 color options per color channel, respectively.
The first part of the aspect - is it a lot or a little?
When viewing a black-and-white image on a monitor screen with a 16-bit color profile - is it necessary? Gray 256 (8 bit color) and 4096 (12 bit) the difference is HUGE! The black and white image was taken on a Minolta Elite 5400 professional film scanner.
An image with 256 shades of gray looks high-contrast, with the loss of a lot of detail (relative to the same image, but with 4096 shades of gray) and this despite the fact that the monitor is able to actually reproduce from 400 to 600 halftones of one color.
Second part of this question Where can you get these pictures.
Firstly, from cameras shooting in RAW format. Secondly - from professional film scanners.
In this case, it is desirable that the image be sent to print as RGB with an accuracy of 16 bits per channel, or as 16 bit grayscale. If your original image had 8 bits per color channel, then you should not specifically convert it to 16 bits per color channel before sending it to print, as this will not add additional details to the printed image.
The third part- Can a high dynamic range image be printed on paper?
It is possible, but relatively conditional. The fact is that photographic paper for printers is capable of reproducing from 30 (thirty) to 450 units of halftones of the same color.
Now let's try to figure out which printers and what paper are capable of reproducing such a large number of halftones.
Paper- any photo paper of PREMIUM class. In particular, from Lomond it can be semi-gloss, super-gloss, satin, among Epson papers - gloss and super-gloss.
Cannot reproduce high dynamic range: matte photo paper, silk matte, plain glossy (not premium).
Printers- again, everything is conditional. The fact is that the least of all have a dynamic range - non-original pigment ink, so to speak, a fee for water and light fastness. But due to the fact that the image is formed not only with black paint, but also with color paint, then not everything is so bad. So the maximum number of displayed halftones of only black ink of pigment ink is 180, and already with an admixture of raspberry ink - this range can already reach 230-320 units (the more, the better). It turns out the effect of compaction - if two paints are poured to the maximum in one place, then the filling percentage is 200%, if three colors are poured to the maximum, then the filling percentage will be 300%, but this does not mean that the dynamic range will increase three times.
Water-soluble, including non-original inks, are capable of producing up to 450 halftones of one color on good papers.
Original pigments, especially if there is a gloss fill, give out up to 280-320 semitones at maximum print quality.
Fourth part- Improved quality of the resulting color profile.
The fact is that when building a 16-bit color profile, all calculations during profile generation are done with an accuracy of 1/65536, against 1/256 with an 8-bit color profile, that is, the accuracy of calculations is 256 times better relative to an 8-bit color profile (0.00001526 against 0.0039). As a result, we get a more accurate color profile at the output, since when performing calculations, more accurate values \u200b\u200bare obtained due to less error. In practice, this means that the midtones are smoother.
Below is the formula for converting to Lab values from XYZ values. Color profiles are based on Lab values. 
As you can see, accuracy in such calculations does not hurt.
WHERE it is relevant:
1 - High requirement for print quality.
2 - Print any images if they are taken in RAW format.
3 - Printing any images obtained by scanning on a professional film scanner.
4 - printing black and white images, and especially if they have a bit depth of 16 bits of grayscale.
5 - If you artificially expand the dynamic range on the image - combine two identical images, with different shutter speeds (light details are worked out on one and shadows are ruined, shadows are worked out on the second image and all light halftones are highlighted).
6 - The newly created image has a bit depth of 16 bits per color channel and contains gradient fills.
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8-bit image, 16-bit image… A scanner with a color depth of 48 bits… Anyone intuitively understands that the greater the color depth, the better something is. But what exactly? And in general - is there any practical use in these figures for a simple car enthusiast?
First, a few basic concepts.
Bit is the smallest piece of information. It may denote
- 0 or 1
black or white
On or Off
Most of today's digital devices work with 8-bit images. It's your inkjet photo printer, and quite possibly even your monitor. That is, almost all the pictures you see are 8-bit.
Small offtopic
If you print a black and white photo on an inkjet machine using only one black cartridge, the quality will be worse than if you print using all the cartridges (four, six or eight - how many do you have there?).
Why is it worse with one black cartridge? Is the image black and white?
Because the printer can reproduce only 256 gradations of brightness - from white to black. For pictures with a large number of halftones and smooth transitions of brightness, this is not enough. The picture looks rough.
If you also use color cartridges, then mixing the three primary colors (magenta, cyan and yellow) can give millions shades of gray (256x256x256). feel the difference
(In fact, everything is somewhat more complicated, but the essence remains - 8 bits is not enough to display even a black and white picture).
How many actually - 8 bits or 24?
Any digital image always consists of 3 primary colors:
- red, green and blue
cyan, magenta and yellow
To store information about each of the 3 colors, 8 bits are used. So to be completely accurate, it would be more correct to call such images not 8-bit, but 24-bit(8x3).
Therefore, an 8-bit image and a 24-bit image are actually synonyms.
8 (24) and 16 (48) bits - two HUGE differences
Instead of just using 8 bit to represent a single color, more advanced devices can sometimes use 12 or even 16 bit.
16 bit image can store 65,536 discrete levels of information for each color, instead of 256 levels to which they are capable 8-bit Images. You can imagine how much more nuance a 16-bit image can convey. If the picture is very complex and delicate, with a large number of halftone transitions, then such a difference can be truly striking.
And just like colored 8-bit 24-bit, as well as colored 16-bit the images are actually 48-bit(16x3), if you remember that they consist of three colors.
Theoretically, a 48-bit image can convey just a crazy amount of color shades. 281474976710656 , to be precise. Not bad…
What are today's microcircuits capable of?
All imaging chips in scanners and digital cameras are capable of generating 24-bit(8x3) images.
Some may generate 36-bit(12x3) photos, and some top models of scanners and cameras can give full 48-bit(16x3) pictures.
Deep color depth has its pros and cons.
How much bullying can a picture withstand?
Often on a monitor, you won't be able to distinguish an 8-bit image from a 16-bit one by eye.
But!
The main moment when the difference between the 8th and 16th bits begins to appear (and strikingly) is during any image editing operation. For example, applying the standby operation Levels or Curves in Photoshop for an 8-bit image can produce much coarser results than for a 16-bit one.
Any image editing operation leads to irreversible loss of information(sometimes barely noticeable, sometimes very noticeable). Sooner or later, this degradation begins to be visible to the eye. A 16-bit image has a much greater "margin of safety" than an 8-bit one.
As big as 65536 is greater than 256.
When the color information of a picture is compressed or stretched when using operations Levels or Curves, the 8-bit file data quickly turns into a sieve, and the histogram into a toothless comb ( as seen in the illustration below). All this leads to posterization. Posterization manifests itself in the form of rough step transitions of color and brightness.
The photo above illustrates this effect well. The range of brightness in this photo is simply huge - from almost scorched, dazzling white clouds to deep shadows on the ground.
In addition, the plot changed every second - the airship either took off or descended, the wind turned it into different sides, people were running, the sun shone in the face, then hid behind the airship. Naturally, it was very difficult to take the perfect picture, and then I had to “finish” it in Photoshop.
Since I was processing a 16-bit image, the final histogram looked more or less satisfactory:
Of course, gaps are visible - information irretrievably lost during processing, but in general everything is alive. And only at the very end, after processing was completed, I converted the image to 8-bit for printing and posting on the Internet.
I tried to do the same operations on the 8-bit version of the image. Compare histograms:
Even if you do not understand what is, it is still clear that there is less information in the "leaky" histogram, and the picture corresponding to it looks worse.
It looks like more than half of the information in an 8-bit image is lost during the editing process. And visually - step transitions appeared in the sky area in the picture - where there should be smooth tonal transitions.
How to get 16 bit image?
16 bit the image from the camera can only be obtained if you shoot in the format RAW.
You pass the RAW file through a special converter program (supplied with the camera, such as DPP or Nikon Capture, or from an independent developer such as Capture One or Raw shooter; By the way, Photoshop can do this too). The converter program converts a RAW file into a 16-bit TIFF file that you can process in Photoshop.
What about those whose camera does not have a shooting mode in RAW?
Converting an 8-bit image to 16-bit mode in Photoshop (Image>Mode>16 Bit/Channel) can help a little. This is the very first thing to do when opening a photo in Photoshop. Of course, such an operation will not make your photo truly 16-bit. But still, the file will become more elastic and resistant to information loss during processing.
What are the disadvantages of a 16-bit image?
First, as already mentioned, You can only get a 16-bit image from a RAW file. (Well, you can still make a 16-bit ersatz in Photoshop, as mentioned above). In any case, this is an additional hemorrhoids. By the way, you most likely cannot view a RAW file with any Windows utility. When storing and sorting photos on a computer, this adds an additional inconvenience.
Secondly, 16-bit files are twice the size than 8-bit ones. This means that they take up more disk space. Well, the RAW file also “weighs” decently, so several times fewer pictures will fit on the memory card in the camera.
Third, some Photoshop features or filters don't work in 16-bit mode(the earlier version of photoshop, the more functions do not work). Therefore, if you have some familiar order of operations when working in Photoshop, you will have to change it. Part of the operations will have to be done in 16-bit mode, and the rest (which is not available in 16-bit mode) - in 8-bit mode.
Fourth, Photoshop can slow down when processing 16-bit files(sometimes - oh-very much to slow down). It's annoying. No less annoying is that in 16-bit mode there is often not enough space on the working disk, where Photoshop keeps its cache. We have to interrupt the work and urgently delete something from this disk so that Photoshop can continue working.
These are not God knows what critical difficulties, but keep them in mind and do not complain that I did not warn you
Practical Conclusions
The highest quality picture can be prepared only from a 16-bit file. This does not mean that any 16-bit file can be turned into a masterpiece. It just means that an 8-bit image will look even worse. Or much worse.
Shoot not just in RAW mode, but in RAW+JPEG mode. Then you will have a JPEG duplicate for each file in the stupid RAW format. It will be much easier for you to navigate through files - view, sort, delete, give. True, for this you will pay extra space on the memory card.
If you are not going to particularly process a series of photos, you can safely use the 8-bit mode (and shoot them not in RAW, but in JPEG).
Apart from this last case, it is always desirable to shoot in RAW mode and process in 16-bit mode.
