Join Lee Varis for an in-depth discussion in this video Lesson 2: Curves and grayscale images, part of Beyond Skin: Going Deeper with Photoshop CS3.
Now we're going to begin to do basic image adjustments and the tool, the primary tool that I'm going to be using is Curves. Curves is the least understood tool, one of the least understood tools in Photoshop, but it's the most important and the most powerful Image Adjustment tool that we have. I'm going to show you how I use it and give you a breakdown on the basic functionality of the Curves, and so that you can understand what's happening when you use a Curve on your image. We'll start by looking at a grayscale image.
No color at all, so we're really only going to be working with contrast, brightness, and tone. All right, so I have an image open here, I have got a black and white photograph, and I've put a step wedge at the bottom. This is a series of steps. I've go 11 steps here that go from black to white and they're all equally spaced grayscale steps.
Now I'm going to go to the Layers palette. At the bottom of the Layers palette, this little circle with a slash cut through it, that's your adjustment layer types. So I'm going to make a new adjustment layer, a Curves adjustment layer. Now we see the Curves dialog. If you're familiar with Curves at all from previous versions of Photoshop, you may notice a few little UI changes. CS3 is full of these little UI changes. They now have kind of a Histogram display in the background of the Curve, and we have also here now Curve Display Options. I open that up, I get to see other controls that we can apply to the curves.
Right now I'm showing the Curve as Light, this little check box here. That gives me steps from 0 to 255, which is what we would use in an RGB file. Some people prefer to use Pigment, and that you'll notice that it reverses the gradients here. Let me do that again. That's where we're dealing with the curve as light values. So as we add light, it gets lighter. If we do pigment, we start off with paper white, and as we add pigment, it gets darker.
This is very comfortable for people that are used to CMYK editing. We're primarily photographers, so I tend to think in terms of adding light, adding exposure, so I like to set up the Curve this way. Now new for CS3, we can Show Clipping. So if I check that, I now look in the image and I can see way down here I have a value that's clipped to black. We can change and clip more of the image, and you can see as I drag this endpoint down, I'm clipping--all of these areas now are clipping totally to black.
Okay, if I select the little white triangle, now I'm showing the areas that are clipping to white. At the moment I don't have very much, but if I move the endpoint over, you'll notice that now I have more parts of the image that are clipping to white. It may not be apparent when you look at the image without the clipping warning that actually some of these high values are now clipped to blank white, usually that's something we want to try to avoid. Now this particular image doesn't really need any adjusting, but I'm using it to show you what happens when you move the Curve, how it affects the image, and importantly, how--what happens down here when we change the Curve.
Now one way that you have to understand what's happening in the Curve is we have an input side of the Curve which is represented by this gradient here, and the output is represented by this gradient. So for instance, if I was to move the endpoint over, let's make it really drastic here, and you can kind of see what's happened down here, I'm losing--I'm clipping values, and I can see that now this is pretty dramatic. I can see it happening in the image here.
What the Curve is telling you at this point, where this lines up with the bottom gradient, this tone is now being remapped to the output gradient as white, up there. And you can see that I've changed this tone, if I uncheck the Preview here, that's what I had before. Now when I apply this Curve, I've clipped all those values to white. All right, so let's get back here to the straight line.
No change is happening at all. All of these values map one-to-one from the gradient down here, all the way along this Curve, it's just mapping one-to-one to the output, so I'm making no change at all. As soon as I move the Curve, I'm going to make a change. So what this is doing now, this simple move is darkening everything, because this line now is below the baseline. So every value from black to white is being darkened by a certain amount here represented by the gap between this Curve and the center line, and you can see in the image that it's all been darkened down.
I haven't clipped anything, because I haven't moved the endpoints, and because I'm dragging in the center, I'm sort of just darkening everything between black and white in equal amount, so I haven't really changed the relationship of the tones to each other. I've just made the whole image darker. So this is a very basic darkening move. Now you ask, what about that famous S-Curve? See, I just dragged that point off. If I drag it off the Curve, it goes away and I'm back at that straight line, so I can start over.
You remember the S-Curve probably from seeing books about film, how the responsive film is, so this is your kind of classic S-Curve. The Curve makes an S shape. And one thing to notice about this is that the center portion of this Curve is still passing through the center of the graph here, and so I haven't really changed the center point with an absolutely mid-gray value in this image.
But I'm increasing the contrast and you can see that in the image. I'm increasing the contrast, because I'm making the center part of this Curve more vertical. So that's one thing to remember. Any part of the Curve that's more vertical is going to have more contrast along that range of tones. And that range of tones, you can see, it starts here, right underneath that point, and ends here, right underneath this point.
So this section of this gradient now has been pushed into more contrast. And in fact, if we take this as our center point, this is medium gray, you can kind of see that as it's progressing out here towards black, it's getting a little bit darker than it was before. So we're increasing the contrast away from the center point here. Look at this area as I uncheck this Preview. So I haven't lost steps yet, but I am compressing these values closer to black and these values closer to white, so I'm getting more contrast in the middle.
Look at that again. See the three steps right in the middle have more contrast. This step is now darker and this step is lighter than the middle gray. The other thing to remember about Curves is that there's no free lunch. If we make a portion of the Curve more vertical, usually some other part of the Curve is going to get more horizontal. So this section here is more horizontal.
We're losing contrast in this part of the Curve. That's these steps right here. Look at that. You can kind of see that this is getting lighter and this is getting lighter, and so they're losing separation from white. Same thing in the bottom part of the Curve, as we flatten it out like this, these values are getting closer together. Now if I make a shape like this, I'm lightening this, everything in the Curve, but I'm actually getting more contrast at the tail part of the Curve here, which is these shadow values.
Look at these values right down here. We have a big step here, whereas before, if I uncheck this, this gray value was closer to black. Now it's further way. I'm increasing the contrast in this section of the Curve, which just has the very low values. These are things to be aware of when you're making Curve adjustments. You can't just use a simple S-Curve all the time to increase contrast, because I'm crushing low values here, closer to black and I may need more contrast down there.
So a simple S-Curve is not always the answer to increasing contrast. You have to know where you want to increase contrast and strive to have a more vertical Curve in that place. So for instance, if we do kind of an inverted S-Curve here, all the contrast is going away in the center part of the Curve and that's kind of where these hands live, and you'll notice how flat they've gotten. I'm sort of flattening out the detail in the hands because they live right in the center of the Curve.
But I'm increasing the contrast in the shadows, so like an area like this over here, has actually more detail, because I'm increasing the contrast there, the difference between this step and black. I'm also increasing the contrast on the highlight side. So the highlights here on the hand are actually getting further away from the midtone values, which are getting closer together here. You can see these steps over here are getting brighter and there's more of a contrast here between this light gray and white, because those are living right here in the vertical part of the Curve.
Okay, this is an inverted S-Curve. It generally flattens out the image, but it's helping the contrast in the shadows and the highlights. You may have an image where that's necessary to do that. The other thing to point out here is right now I have a full range image. I've got tones that go from black to white. A lot of times you'll get an image where the darkest tone is maybe this step right here.
In that case, I'm going to--you'll see I'm going to pull the endpoint over until this step goes to black. All right, so now these two values have merged together and that's my new black point. The best way to increase contrast if you don't have full range, which is usually why we would want to increase the contrast, is to just move the endpoints.
Then we're going to get--I'll save this, this tone was the lightest tone in your image. I'd move the endpoint over until I get that to go white. Now these two tones merge together and I've got maximum contrast through the range in the image from here to here, because I've actually made the Curve more vertical. And you can kind of see here, we've lost some deep shadow values separation, but we've really enhanced the contrast in the hands.
This part is straight line, more vertical than it was before. Now if you hold down the Option key, you'll notice that the Cancel button now becomes a Reset. So I can always get back to my Neutral Curve by holding down Option or Alt if you're on a PC, and clicking the Reset button. Okay, if we lower the endpoint, I'm going to make that white grayer.
If I raise the shadow point, I'll make the black grayer and now we're just overall softening the contrast and we have a more horizontal Curve. Very rarely we see this occurring, but in some special applications we may use a shape like that. Mostly, we're usually looking to increase the contrast and so we're usually looking for the most important parts of the image to be in a more vertical section of the Curve.
So this is the basic operation of the Curve control. We have options for the UI, you can turn --the grid spacing can be changed from a wide space to small space here. And a couple of these other things we can turn on and off. This is the default state of the Curve where everything is showing. I can turn off that Histogram. If it's bothering me, I just turn it off. The intersection line which is not visible unless we've made a change to the Curve.
Here is the Baseline. That's the straight Curve, so we have a reference. When we've made a change, we can always see where it was. It's always this straight line. You can turn that on or off. The intersect line is where the Curve intersects. So for instance, where the Curve intersects, we have an intersect line.
And the Histogram shows you the distribution of values and you can kind of see, and it really is like the histogram display, but it's inside the Curves dialog, so it has the square shape instead of a horizontal rectangle. But it's giving us a distribution of tones in the image and you can kind of see generally by the shape of this Histogram that this image has a lot more dark tones, which are over in this section of the Curve. So I may want to, for instance, lighten up just that section of the Curve and I know that this is an area that is of interest and I'm steeping the Curve at that point and also moving it up to make it lighter.
In general, that's about as useful as this Histogram gets. We're going to be looking at a more precise way of adjusting images than using the histogram. So I generally find that the Histogram is not that useful. Okay, so we're going to be looking at a more precise way of analyzing the image than we get from the Histogram. So I generally turn the Histogram off, just because I don't need to see it when I'm working with Curves and it actually will slow down Photoshop just a little bit, as it has to update that Histogram when you make a change.
So at this point, we can Reset back to Normal. I don't want to change this image at all. The next step in working with Curves is to actually start working in color and what we're going to discover is that when we work with an RGB image, a full color image, what we're dealing with is actually three black and white versions of this image. The Curves work on those black and white versions the same way I've shown here working with this black and white image.
Only they are working with the individual channels of a color image, so different curve shapes and different channels are going to give us different results for our color. And we have very, very fine control over what happens with the color, in essence, by manipulating the grayscale channels of the full color image.
Portraiture can be one of the most rewarding skills for a photographer to master, and the right post-processing and enhancement techniques can make all the difference. In Beyond Skin: Going Deeper with Photoshop CS3, Lee Varis uses Photoshop CS3 as a digital darkroom to bring out the best in photos of people, faces, and bodies. He examines tone and contrast, color correction, retouching, and more.
- Customizing the Photoshop CS3 workspace
- Controlling tone and color balance with Curves settings
- Correcting and enriching color with Hue/Saturation
- Converting images to black and white
- Retouching and sharpening portraits
- Enhancing background bokeh
- Adding portrait glow
- Blending luminosity