Join Taz Tally for an in-depth discussion in this video Understanding grayscale values and color, part of Photoshop Color Correction: Advanced.
In this chapter, we want to have a discussion about how to measure color and how to correct color. Particularly quantitatively, that is using numbers. In the fundamentals course, that preceded this one, we talked a lot about histograms and using histograms to evaluate the color in an image. And we're going to use histograms again here too. But we're going to use them in combination with numeric values using our Info panel. So if you have not viewed the original fundamentals course and learned about how to evaluate histograms at this point I would encourage you to go back and review that portion of the fundamentals course at least that portion to learn how to evaluate histograms.
Cause we're going to start talking about numbers and using the Info panel and we're going to marry that back into using the histogram in just a couple of movies. So, that said, let's dive right in to talk about gray-scale values and how gray-scale values affect color. When we look at a color image, like this one, there's lots of different colors in it. We tend to be thinking, oh this is a color image, right? And, for a lot of people, this is why color correction can be pretty intimidating because they think. Oh my gosh! What are those RGB values supposed to do, and use? And what do they mean? And then someone tells them that there are 16.7 million colors in their file.
And then, you know, their eyes roll back in their head and they start, you know hyperventilating. Well, when we break it down to the fundamentals, the basis of what really controls color, you're going to see that it's far simpler than that. So, the first point that I want to make here, is that there is no such thing as a color image in terms of capturing or actually editing it in Photoshop. When you capture an image, either with a scanner or a digital camera, they're called digital devices for a reason. The word digital means that, that image is broken up into zeros and ones. Alright? There's only two digital values, zero and one.
Black and white, and that's the only thing we can actually assign to an image, is grayscale values. Now you may be thinking, hello, Taz, there's a color image up on-screen here. I don't see any grayscale, but watch. When we bring up, as we have here, we have an Info panel and we have channels. Channels are the building blocks of the image, and this is the RGB image that we're viewing right here. But the really foundation for this image are these three channels right here, the red, the green, and the blue. And when we look at these three channels, what do we see? Nothing but grayscale, because that's really how this image is built up.
So, you ask, where does the color version come from? Well here's the fundamental truth about digital color and it applies to any device you want to think about. All color is actually created by output devices. Think about it, if you've got that four-color inkjet printer that's sitting on your desktop, you'll open up the top, you look inside, there's four ink containers. Cyan, magenta, yellow and black. That's where the color's actually applied. On your screen, these are RGB monitors. And the red, the green, and blue colorants that we use to combine to create an image on-screen are provided by the monitor.
On any video device, on any printing device, the color is provided on output. So what are we actually capturing? What are we actually viewing and editing? It's grayscale. The second fundamental truth about color is not only is all color created by output devices, but all color is controlled by grayscale. If we get the grayscale values correctly in an image then the color is going to be correct on output. And when you understand this fundamental truth that we're working with grayscale here and then color is created in our output devices then it becomes pretty clear why images can look very different on screen than they do on a printing device.
Right, because here we're taking these grayscale values, and we're actually painting them with red, green, and blue colorants on, like a glass or plastic screen of some sort. Whereas when we go to an output device, like a printing device, we're printing with cyan, magenta, yellow and black inks on paper or plastic or glass or something. So the colorants, the substrates are different. And that's what color management is all about, is trying to match up those different devices. When we do color correction, our fundamental job is to get the grayscale values correctly in our image, based upon the grayscale values in the image.
If we do that, if we get the grayscale values correct, then we have a much better chance of being able to predict what the color is going to be on our output device. And if we're working with calibrated monitors, then the color in the image is going to match what we see onscreen. So we're all about the grayscale values. So we're going to go into our images and we're going to evaluate what the red, green, and blue values are in quotes based upon, actually, the grayscale values that exist on each of these three channels. So, just to sum up, what we actually captured with the scanner or digital camera is three channels of grayscale that we call red, green, and blue.
But in fact, they're grayscale. And then we paint those values, in the case of the monitor that you're watching right now, with red, green, and blue colorants. So we're going to be all about measuring and correcting the grayscale values in the image. Alright, having said that now. Let's move to, our fundamentally important tool for measuring and adjusting numeric values in the image. And that's what, the fundamental difference is between the fundamental color correcting class in Photoshop and this advanced class. It's here, we're going to use a lot of the same fundamental tools to evaluate our colors, such as histograms, but we're going to add in a numeric analysis of color.
So, when you want to get it right on the money, you do it numerically. You know you're going to be right. You're going to have great confidence in this. But first to do this, we need to understand what these RGB values stand for and what they mean. To help us with this, remember, keeping in mind that everything is grayscale, I want to move to this target here, and this same target is available for you to use. You can open this up inside of Photoshop, and view it and measure it just like I'm doing here. And what I've done is I've created a very simple three target file here.
The far right is pure white, the far left is pure black. And in the middle is a midtone gray. And I want to use this simple target to help describe how the Info panel works. so I'm just going to move the Info panel close over here because it's easier for us to see. And notice that I got the first portion of the Info panel set up here to measure RGB values. Alright, you can click and choose different ways of measuring color. And we're just going to choose the Actual Color RGB. And I'm going to move my cursor over here. I'm choosing RGB because this is the standard color workspace that we work in, in Photoshop.
And the first thing that's very important to understand is that unlike other, say, editing programs like Lightroom, which uses a zero to 100% scale. In Photoshop the standard default scale is 0-255 and it's 256 shades of grey that we're working with. So notice when I put my cursor over this pure white swatch that you see here it measures 255 over here on the RGB scale. That means 255 on each of the grey scale channels. When I move my cursor all the way to the left the RGB values measure zero, and when I put it in the middle it measures 128, which is one half the way between 0 and 255.
So, when we're measuring RGB values in an image, alright it's going to be somewhere between 255 which is pure white and 0 which is pure black. And if you're thinking, hey that's the complete reverse from a 0 to 100 scale, right where 100% black is pure black and then 0 is pure white. I know, I get it, don't blame me. It's not my fault. It is the inverse scale of this 0 to 100%. And you just have to kind of get used to working in 0 to 255 and think of 255 as pure white, 0 is black, and 128 is midtone gray.
So, that's how the RGB values work in an image. So now, when we move over to an actual quote unquote color image that has grayscale values in it, on each of the channels, and we start measuring the quote unquote again color values in an image, when we move our cursor over like this yellow boot, watch the RGB values. And here, I'll just move this over here so it's easy to see. Here we put this on a pretty solid yellow color. Its R 201 green 185 and blue 60 alright, and doesn't that make sense? because yellow was made up primarily of red and green right with very little blue and on the scale of 255 the 200 is about three-quarters of the way there.
Right the 185 is a little bit less and the blue the 60 is very very low. Alright when we move over a red, alright. The red value is very high. The green and blue are pretty low. When we move over something that's got a lot more blue in it, alright, over here, alright, the blue value is high, 127. Green is lower and red is lower still. So, depending upon what color you're on, we're going to have different amounts of grayscale values. So that's how the Info panel works when you set up its RGB and that's what the RGB values means in terms of grayscale.
0 to 255, where 255 is pure white. 0 is pure black and 128 is somewhere in between. Notice on this one is blue that we're measuring, the blue is actually right at 127 so that's the percentage of being a mid-term grey in terms of the blue value in the image. So, this is the tool that we're going to evaluate the grayscale in order to get our color correct.
- Using color workflow tools: Bridge, Photoshop, and Camera Raw
- Setting color workflow settings
- Setting up a monitor and viewing options
- Assigning a workspace and color keyboard shortcuts
- Understanding grayscale values and color
- Working nondestructively
- Working with neutrals
- Using targets for color correction
- Evaluating tone and color
- Evaluating and correcting skin tones
- Working with color sampler points and Curves efficiently
- Adjusting tone and color
- Performing target-based corrections
- Sharpening a color-corrected image in Photoshop