From the course: Photoshop 2024 Essential Training

Mastering bit depth and color mode - Photoshop Tutorial

From the course: Photoshop 2024 Essential Training

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Mastering bit depth and color mode

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- [Instructor] We're going to take the next few minutes to look at several images that have various bit depths and color modes. Bit depth specifies how much information is available for each pixel in an image. The more bits of information per pixel, the more values are possible and the more accurate tonal representation can be achieved. The most common bit depths are 8 and 16 bit. Color mode determines how many colors can be represented by the number of channels that they contain and the way that colors are stored in those channels. We're going to look at three color modes, grayscale, index color, and RGB, and how they interact with bit depth. This first example is an 8 bit image in the gray scale color mode. In 8 bit, the gray scale image can have 256 possible values. It's limited however to one channel, but in most instances, 256 shades of gray represents an adequate number of tonal levels to display what appears to be a continuous tone, black and white, or more accurately, a gray scale photograph. The second example is the index color mode. It's similar to the gray scale mode in that it can contain 256 possible values and it's limited to a single channel. However, the values in index color are colors, not shades of gray. A single channel helps keep the file size down, which is ideal for creating ad banners or similar images to post online. But in most instances, index color mode will not be able to display a large enough spectrum of colors to render a continuous tone photograph. Now to try to appear continuous tone, the 256 colors can be customized. They can be customized on the colors in the image, or they can be mapped to specific color palettes and different types of dithering, which is the process of alternating two or more colors can also be used to help simulate additional colors. But as we can see in the enlarged preview, index color mode is prone to banding in subtle areas of gradation and it doesn't hold up well when enlarged or when significant editing is required and done to the photograph. So the third color mode is RGB. Similar to the gray scale and index color modes, an RGB image can have 256 possible values, but the key difference is that RGB images have three channels, a red, a green, and a blue channel. Whereas the previous color modes were limited to a single channel. With 256 possible values in each channel, 8 bit RGB images have over 16 million possible colors and can in most instances represent a continuous tone color photograph. However, 8 bit RGB images obviously don't represent all of the tonal values or the colors in the world. There are certain values that aren't represented at all, which can result in an inaccurate representation of a scene. To help solve this problem, we can work with both 16 bit gray scale and 16 bit RGB images. A 16 bit per pixel gray scale image can contain over 65,000 shades of gray, far more than that mirror 256 values possible in the 8 bit gray scale image. And a 16 bit per pixel RGB image will have over 65,000 possible values for each channel. So literally trillions of colors to work with. However, 16 bit actually exceeds both our ability to perceive color as well as the number of reproducible colors. So if the added bit depth is beyond our ability to perceive and the 16 bit increases the size of the file, then why would we want to work in 16 bit? Because they have the potential for maintaining a higher quality image and withstanding greater manipulations when editing. So if we look at this original image and we look at the histogram and a histogram basically maps the values in an image from black on the left to white on the right, and we'll be discussing histograms in more depth in later videos. But for now, notice that it's nice and smooth. There are no gaps, and if I'm editing an 8 bit file and I need to make big changes to it, for example, I need to lighten the image and add contrast, well then we're going to get these gaps in the histogram. And these gaps represent areas in the image where there are no color or tonal values. And if these gaps get too large, then the quality of the image will decrease and we'll most likely see banding or distinct breaks between different colors in areas of the image. If on the other hand I'm working with a 16 bit image, I have far more latitude when making those same edits to the file and we won't see those gaps in the histogram. I should also mention, although it is beyond the scope of the essential training course, Photoshop does support 32 bit images, which are primarily used in the film and gaming industry when rendering 3D objects and creating computer generated imagery for special effects. Alright, let's take a look at bit depth and color modes in Photoshop. When I create a new document in Photoshop, we can choose both the color mode as well as the bit depth that we want to work in and then create that document. We can see that it's opened up as an RGB image in 16 bit if we look at the title bar. Now let me move to Bridge and I'm going to open up this JPEG file of the thistle. Here, we can see that it is an RGB file, but it's an 8 bit because the JPEG file format only supports 8 bits. If I return to Bridge and this time I want to open the cactus.dng file, well, it's going to open up into Camera Raw because it's a raw file and I can use the workflow settings in order to set the bit depth of the file. I'll go ahead and open that. And if you're using Lightroom Classic or Lightroom instead of Camera Raw, those applications are set by default to open the raw files into Photoshop as 16 bit. Now, if we need to change the color mode or the bit depth in Photoshop, I can use the image menu, select mode, and then select my color mode as well as my bit depth. We can see however, that I can't access all of the color modes, and that's because I'm in 16 bit. So if I wanted to go to index color, for example, well I'd need to change the file to 8 bit first. Once I do that, I can return to image and then mode, and now I could go to index color. One thing to note, if I'm converting from a higher bit depth, like 16 bit down to 8 bit like I just did, Photoshop will need to discard information and it's a lossy conversion that can't be fixed by going in the other direction. So for example, once I've gone to 8 bit, even if I return and choose 16 bit, Photoshop can't make back up that information. It's not going to magically add the higher quality. Also, most raw files aren't actually 16 bit, they're 12 or 14 bit, and we can see that in the metadata panel that this file has a bit depth of 14. But in Photoshop you can only open them as either 8 or 16 bit. So for the most part, choosing the correct bit depth comes down to the file size versus flexibility and quality when editing. An 8 bit image will be smaller than a 16 bit image. However, 16 bit and 32 bit images contain more information and can produce higher quality results when large edits are made to an image. I prefer to work in 16 bit whenever possible. A larger file seems like a fair trade off for more colors and tonal information when I'm making my edits to my images. If you're using the exercise files for this course, you'll notice that a lot of them are in 8 bit, but that's just to try to keep the file size down.

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