Your First Basic Curves Correction

Tutorial by Ed Ladendorf

I downloaded a very good image from our archives to give you an idea of what can be done by using nothing more than one curves adjustment layer and a selection. Hopefully, this will give you the incentive to learn how to use curves. Here’s the image, before and after.

Let me make it clear, there’s a lot I don’t know about using curves. But maybe I know enough to bluff my way through a tutorial. If anyone has negative feedback, please feel free to post. Some basics will be discussed, followed by a tutorial where you will get hands-on practice to make basic tonal corrections to an image. If you want the hands-on practice, you will need to download this image by clicking here. This image could easily be corrected by using levels. We will use it because you have to learn to walk before you run. It should provide good practice.

If you are new to using curves, the curves dialog box always starts out with a 45 degree line through the box (unless it is an adjustment layer that has already been adjusted), which indicates the input and output (the before and after) when making adjustments. This line represents all tones in the image, and it goes from 0 (black) to 255 (white). You will see 2 gradients, one at the bottom, and one at the left side of the dialog box. The bottom gradient has an arrow that you can click on to reverse the order of black and white on the gradient bars. It can be used either way, but for this exercise (and my personal preference) the white will appear at the top of the gradient bar on the left side of the box. If you pick any point on the diagonal line, and look straight down at the bottom bar, you will see the tonal value that point represents in the image, before making adjustments. If you take that same mark, and look straight over at the left bar, it will indicate what the tonal value will be when you accept the proposed adjustment.

If you have not made an adjustment, it will indicate the same tonal value as the bottom bar.

With the gradient set with the white at the top of the left bar, if you move any point up, that point will become lighter You will be taking the tonal value indicated on the bottom bar, and making it lighter, as will be seen on the left bar. Take the point down, and it gets darker..

This tutorial assumes that you have set the gradient bar on the left side of the curves dialog box so that white is at the top of the bar. The numbers I mention will not necessarily be exactly the same as yours, but yours should be close. If they’re not, something is wrong. At the bottom right of the dialog box, you will see the image of a pencil, and another of an adjusted curve with dots. Make sure you have the adjusted curve with dots selected. The other one allows for freehand drawing of curves, and I never use it because I feel the other is better for retouching/restoration. If you have the pencil selected, you will not be able to follow the exercise.

We will use curves (without using the eyedroppers) to make a tonal correction on an image that was downloaded from the archives. Download this image to follow along with the exercise, if you haven’t already done so (it’s the same one as appeared above). Now let’s make your first tonal corrections, while using curves.

Open the image, and make a duplicate. (IMAGE/DUPLICATE). Minimize the duplicate by clicking on the box in the upper right corner of the image. We are now back to the original image. Make a curves adjustment layer. (LAYER/ADJUSTMENTLAYER/CURVES) We will be looking for the darkest part of the image. We find it by clicking and holding anywhere on the image, then while dragging the cursor around, we observe where the dot is moving in the curves dialog box. When the dot is closest to the bottom, we have found the darkest point in the image. I found this to be in the pants of the snowsuit. When you find that point, Ctrl/click on that point in the image. This will set a dot on the grid. Using the down arrow, move this dot down until the output reading is 12. The image already looks better. Click on OK.

The shadows in the face are too dark, and if we lighten them, other areas of the image will benefit also. Make another curves adjustment layer, as you did above. You now have a diagonal line across the grid, as you did when you entered the dialog box for the first time. Hold down the control key, and click on the facial shadow above the eye. This will set a dot on the line, indicating where this tone lies on the grid. My dialog box tells me that the input value is 81. Using the up arrow key, raise the dot until you see the number 103 in the output box. The shadows now look much better, and you have brought out some detail in the upper part of the snowsuit.

But we don’t need two curves adjustment layers, and a single one will better show what is happening with your corrections. Do not close this image, but minimize it, and maximize the copy. We will do things much in the same way as we did the original, but we will use only one adjustment layer this time. Make a curves adjustment layer, and find the darkest part, like you did before. Control/click on this part of the image. This once again places a dot on the grid. Using the down arrow key, move this dot down until the output reads 12. The image should look the same as when you did it the first time. Do NOT click OK. Target the shadow above the eye as before, and click on it while holding down the control key. My input value reads 159. What’s going on here? The last time I clicked on that part of the image, my reading was 81! Here’s what happened. The first time you corrected the image, you used two adjustment layers. After you took the dark point, and moved it to an output value of 12, you said OK. Now, when you made another adjustment layer, the value that was originally 96 now reads 12, and it is near the bottom left corner of the grid. The facial shadow area input read 159, and it now reads 81. It has become much darker, along with the point you moved down.

Maximize the original image, and double click on the first adjustment layer. This will bring the dialog box back up, with the corrections you made. Since this is an adjustment layer, you are able to modify any changes you made (but we’ll leave it as is). Hold the mouse button down on the facial shadow area of the image. Control/click on this point in the image, and you will see another dot appear. Do NOT move it, but look at the input/output values. Mine reads 159/81, meaning that area became darker when I made the first adjustment. Once you have verified that, hold down the shift key, and drag that dot off the grid. You don’t need it any longer. Now you know why the shadow area had an input value of 81 when you made the 2nd adjustment layer. You made that area darker when you clicked on OK the first time. When you made a new adjustment layer, this now darker input value shows as 81. Minimize the image. The reason this area now reads 159 is because you have not yet committed to the change. If you take that dot, and look straight up to where the original diagonal line was, you will see that the value was, in fact, 159. At least mine is, and yours should be close. Click on this dot, and using the up arrow key, move it until the output shows a value of 103. Click OK to accept the changes.

This image now looks exactly like the first one, but we only used one adjustment layer, and it’s easier to see what’s happened with our corrections when looking at the dialog box. Checking the light area on the shoes, shows me that it has a value of 243, which is good. No further adjustment is necessary. Here’s what my finished image looked like:

There are a few other things you should remember:

1. The steeper the line is between two dots in the dialog box, the more contrast there is between those areas. Keeping this in mind can help you bring out detail, locally.

2. The flatter the line is between the two dots, the more similar those tones will become, resulting in a loss of contrast and detail in those areas.

3. If your curve has a section where it slopes downward, your photo will probably look pretty bad in the tones that fall along the downward slope.

4. If, while making adjustments, you see a part of your image that has become bad, click/hold, and drag the cursor around that area in the image. You will probably find that the problem area will be apparent on the grid.

5. When you make adjustments to make something look better, you lose something in another part of the image. Typically, adjustments are made to make the midtones look better, while accepting some loss of detail in the shadows and/or highlights. But this is not always the case, You have to decide where to make the corrections.

6. It’s a good idea to keep an eye on the grid for the lightest and darkest areas of importance, when making adjustments. Otherwise, these areas could be pushed to pure white or deepest black.

Knowing what you know now, see if you can figure out what this curve would do to the corrected image you just made. If you can’t, ask questions. We have a lot of members who will gladly explain.

Enjoy!

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