Benefits Of Working With 16-Bit Images In Photoshop
Learn The Difference Between 8-Bit Color And 16-Bit Color In Photoshop
As we just learned, saving a photo as a JPEG creates an 8-bit image, which gives us 16.8 million possible colors in our image.
That may seem like a lot, and it is when you consider that the human eye can't even see that many colors. We're capable of distinguishing between a few million colors at best, with some estimates reaching as high as 10 million, but certainly not 16.8 million. So even with 8-bit JPEG images, we're already dealing with more colors than we can see. Why, then, would we need more colors? Why isn't 8-bit good enough? We'll get to that in a moment, but first, let's look at the difference between 8-bit and 16-bit images.
On the previous page, we learned that 8-bit images give us 256 shades each of red, green and blue, and we got that number using the expression "2 to the exponent 8", or "2 x 2 x 2 x 2 x 2 x 2 x 2 x 2", which equals 256. We can do the same thing to figure out how many colors we can have in a 16-bit image. All we need to do is calculate the expression "2 to the exponent 16", or "2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2", which, if you don't have a calculator handy, gives us 65,536. That means that when working with 16-bit images, we have 65,536 shades of red, 65,536 shades of green, and 65,536 shades of blue. Forget about 16.8 million! 65,536 x 65,536 x 65,536 gives us an incredible 281 trillion possible colors!!
Now, you may be thinking "Gee, that's great and all, but you just finished saying that we can't even see the full 16.8 million colors that an 8-bit image can give us, so does it really matter than 16-bit images give us trillions more colors we can't see?"
When it comes to editing our images in Photoshop, it most certainly does matter. Let's see why.
Editing In 16-Bit Mode
If you had two identical photos open on your screen in Photoshop, the only difference being that one version was in 16-bit mode with its trillions of possible colors and the other was in 8-bit mode with its 16.8 million possible colors, you might think that the 16-bit version would look better, since it's capable of displaying far more colors than the 8-bit version. But the simple fact is, most photos don't need 16.8 million colors, let alone trillions of colors, to accurately reproduce their contents. They usually contain several hundred thousand colors at best, although some may reach into the low millions depending on their subject (and depending on the size of the photo as well, since you would need millions of pixels in order to see millions of different colors). Plus, as we've already learned, the human eye can't see 16.8 million colors anyway, which means that when placed side by side, an 8-bit version and a 16-bit version of an identical image will look identical to us.
So why, then, would it be better to work with a 16-bit image? One word - flexibility. When you're editing an image in Photoshop, sooner or later, if you continue making edits, you're going to run into problems. The most common problem is what's known as "banding", where you've lost so much detail in the image that Photoshop can no longer display smooth transitions from one color to the next. Instead, you get an ugly stair-stepping effect between colors and tonal values.
Let me show you what I mean. Here's a couple of simple black-to-white gradients that I've created in Photoshop. Both gradients are identical. The first one was created as an 8-bit image. You can see the number "8" circled in red at the top of the Document Window which tells us that it's currently in 8-bit mode:
And here's the exact same gradient created as a 16-bit image. Other than the fact this this one says "16" at the top of the Document Window to indicate that it's in 16-bit mode, both gradients look the same:
Watch what happens to them though when I edit them. I'm going to perform the exact same edit on both. First, I'm going to press Ctrl+L (Win) / Command+L (Mac) to bring up Photoshop's Levels adjustment, and without getting into a lengthy discussion of how Levels works, I'm just going to drag the bottom black and white "Output" sliders in towards the center. Again, I'm going to do this with both gradients:
What I'm essentially doing here is taking the entire range of the gradients from pure black on the left to pure white on the right and squishing them into a very small section in the center which is normally where you'd find the mid-range grays. I haven't actually changed the gradients. I've just forced their entire tonal range into a much smaller space.
I'll click OK to exit out of the Levels dialog box, and now let's take a look at our two gradients again. Here's the 8-bit gradient:
And here's the 16-bit gradient:
Both gradients now look more like solid gray after the Levels adjustment, but they also still look identical at this point, even though the top one is in 8-bit mode and the bottom one is in 16-bit mode. Watch what happens though when I use Levels again to stretch the tonal range of the gradients back to pure black on the left and pure white on the right. I'm going to drag the black and white "Input" sliders in the Levels dialog box in towards the center this time to force the darkest parts of the gradients back to pure black on the left and the lightest parts back to pure white on the right:
Let's look at our two gradients again. First, the 8-bit gradient:
Ouch! Our smooth black to white gradient doesn't look so smooth anymore! Instead, it has that "banding" or "stair-stepping" effect I mentioned, where you can very easily see where one shade of gray changes to the next, and that's because we've lost huge chunks of detail in the image after making those edits with the Levels adjustment. So the 8-bit image didn't survive very well at all. Let's see what happened to our 16-bit gradient:
Look at that! Even after the rather drastic edits I made with Levels, the 16-bit gradient survived without a scratch! Why is that? Why did the 8-bit gradient end up losing so much detail while the 16-bit gradient did not? The answer goes back to what we've been talking about up till now. An 8-bit image can only contain a maximum of 256 shades of gray, while a 16-bit image can contain up to 65,536 shades of gray. Even though both gradients looked identical to us when we started, those 16 thousand plus extra possible shades of gray gave us a lot more flexibility with our edits and made it far less likely that we would see any problems in the image afterwards. Of course, even with 16-bit images, there could eventually come a point where you've lost enough detail that you can see problems if you're performing a ton of edits on an image, but with 8-bit images, that point will come much sooner, and with 16-bit images, we're talking much, much later.
Let's try the exact same thing with an actual photo this time.
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