Improve Print Tones through Better Curves Layers

These Advanced Photoshop Techniques Can Fix Poor Exposures

By Ctein Back to


All experienced printers know the First Rule of Good Tonality: a good print, whether black-and-white or color, almost always has a range of tones that run from near-to- white to near-to-black. This is true even of high-key and low-key photographs. This dictum holds so often that the exceptions to the rule are, well, exceptional.

By itself, though, this isn’t enough to ensure great-looking prints. Most fine prints require some degree of local control of tones. This article talks about making such improvements in the context of fixing old photographs, but the methods apply just as well to new ones. Many photographs made outside the studio, where one has little control over lighting, have one or more of the problems I address here. Frankly, in my opinion, there are few real-world photographs that don’t benef it from some dodging or burning-in.

Correcting uneven brightness and contrast

The photograph in Figure 1 was very badly made. Aside from the usual low-contrast printing typical of black-and- white photofinishing in the mid-20th century, it was improperly exposed. The flash sync on the camera was set incorrectly, so only the right side of the picture got good flash exposure. The easiest and best way to correct uneven exposure like this is with a Curves adjustment layer combined with a mask to control what parts of the picture are altered. You create an adjustment layer by going to the Layer menu, selecting “New Adjustment Layer” from the drop-down menu, and picking the kind of layer you want to create (Curves, in this case)

While creating the Curves adjustment layer, I didn’t make any curve changes. When the Curves tool opened up, I merely clicked “OK.” I did that because I wanted to first create a mask for that layer so that the properly exposed part of the picture wouldn’t be changed. That way, when I experiment with different curve settings to correct the left side of the photograph, I can see how well I’m matching the right side.

I set my foreground and background colors to white and black and selected the Gradient tool (Figure 2). I chose “Foreground to Background” as the gradient type, made sure that the Linear Gradient button was pressed, and left the mode normal and the opacity 100%. I created the gradient by drawing a horizontal gradient line from left to right, starting under the baby girl’s nose and extending almost to the boy’s arm. That was my best guess of where the exposure fall-off began and ended (Figure 3). The black area on the right side of the gradient is completely masked off; there the adjustment layer has no effect. As the gradient fades to white, the effect of the adjustment layer increases until it becomes 100% for the left portion of the picture.

The advantage of doing this with an adjustment layer and a mask is that I don’t have to get this correct on the first try; I just have to make a usefully close guess. If I discover that this won’t give me the uniform exposure correction I’m after, I can modify or replace the gradient in the Curves mask channel. Now I’m ready to correct the exposure.

I didn’t do anything fancy to come up with the adjustment layer’s curve in Figure 4. I just moved in the white point until the highlights looked about the same on both sides of the photograph in the preview. Then I dragged in the black point until the shadows looked similarly dark. That left the midtones on the left side a little too dark, so I added a center point to the curve and raised it up a bit to lighten those tones so that they matched on both sides of the photograph.

Figure 5 shows the results of my efforts. My first attempt at a gradient mask turned out to be pretty good. There’s a slightly darkened band between the two girls where the Curves adjustment wasn’t quite strong enough. I fixed that by lightening up the mask along a vertical band in that area. I just painted a stripe down the mask with a wide-radius white Airbrush tool set to 5% opacity, nothing more complex than that.

It was only a slight correction; Figure 6 shows the original gradient mask in the top half and the airbrushed mask in the bottom half. The alteration is so subtle, in fact, that I’m not attempting to reproduce the difference it made here. I bring it up only to illustrate the level of refinement that’s easily achievable when you use these kinds of masks.

Figure 5 isn’t anywhere close to being a finished work, but evening out the exposure was the critical first step. By the way, this is a good example of the need to work in 16-bit mode. The contrast adjustment I made to the left side of the photograph threw away almost two-thirds of the value range. Expanding an 8-bit image’s contrast by a factor of three would produce very visible and unacceptable contours.

Dodge and burn with masked adjustment layers

It’s not much of a conceptual leap from using gradient masks to control local photograph densities to using any kind of mask, including hand- painted ones.

Hand-painted masks are uniquely valuable because they let you apply correction effects exactly where you want them. The effect can be as broad as half a photograph or as narrow as a single pixel; it’s just a matter of what radius brush you use to paint the mask with.

You can apply any kind of Curves alteration you want this way, but I’m going to concentrate on the two most useful ones. I call them “dodging” and “burning-in” masks (and layers) because they produce effects a lot like dodging and burning-in does in darkroom printing. Unlike darkroom printing, you can have as many different dodge and burn-in effects as you want by creating a new adjustment layer for each particular f lavor of alteration you want to make. Also, unlike darkroom manipulation, this approach can adjust local contrast as well as brightness.

This dodging and burning-in is reversible. If you find you’ve overdone the correction at some point, just paint over that part of the mask with a black brush to reduce or eliminate the change there. This requires no painterly skills. The better you are with wielding a (digital) brush, the more efficiently you’ll be able to do this, but you can erase or rework any mistakes you make. You’ll always be able to get there bit by ref ined bit.

Good dodging and burning-in curves are hugely exaggerated adjustments. They’re intentionally super-strong so that you can paint them into the layer mask with a low-opacity brush, building up the changes you want stroke-by-stroke in a controllable way.

The photograph in Figure 7a is a good candidate for burning-in and dodging. The original negative was apparently light-fogged. Large parts of the lower half of the photograph are washed out and pale, although low-contrast detail is visible in those areas.

For the first round of repairs on this image, I created a Curves adjustment layer with the curve shown in Figure 8. This extreme correction greatly increases the contrast and density of any tones below light gray. I designed this curve to produce such a strong change that it could fix the flare problem in all but the worst spots. It doesn’t matter that it’s too strong for most of the photograph because I’ll be painting in the adjustment only where I want it and at the strength I want.

Next, I inverted the layer mask to make it black instead of white. I selected the Brush tool and gave it a radius about two-thirds the size of the largest areas I wanted to burn-in. I set the opacity of the brush to 12%; I’ve found that values between 8% and 15% work best for doing dodging or burning-in. I did not turn on the mask-layer visibility. There’s no need to see what the mask layer looks like, only the effect of the brush on the photograph.

I made a couple of passes at the mask layer with the large-radius brush to dampen the overall flare. Then I switched to a smaller-radius brush and started filling in the places the large- radius brush had missed. When that was close to correct, I switched to an even-smaller-radius brush to touch up the areas that still needed to be toned down. If I went too far and made an area too dark, I switched the brush from white to black and painted some of the mask back in to reduce the over-adjustment in that area.

I find that working back and forth between black and white brushes like this and shrinking the radius of the brush as I refine the adjustments is a very efficient way to do this kind of painting. This is just my style, however. If you want to take a different approach to painting in the mask, do whatever feels most comfortable and efficient for you.

Only a few minutes work got the photograph to Figure 7b. The burn-in mask is in Figure 9. It looks strange, doesn’t it? Still, it does the job and does it well.

I created a second burn-in adjustment layer to deal with the flare patches that the first layer didn’t entirely fix, mainly a flare spot at the lower right corner of the photograph. I assigned the curve in Figure 10 to that layer. It darkens most of the tones, but also greatly increases contrast in the lighter areas so it could make the flare spots both darker and more contrasty and even improve the whites a bit. The burn-in mask in Figure 11 got me to Figure 7c.

Next, I needed to do some dodging along the lower edge of the photograph where there was a very dark strip. I created a third adjustment layer with the curve in Figure 12. This curve leaves the black point unchanged but extremely lightens everything else. When I was done dodging the dark areas that needed correction, shown in the mask in Figure 13, I had Figure 7d.

That finished the technical correction I set out to make. I still saw room for artistic improvement. I felt that several of the faces and the white clothing were too washed out. I wanted to increase their contrast and make them darker, but I didn’t want the highlights to go gray. In fact, I wanted the highlights to be a little brighter.

I created my final masked correction layer with the curve in Figure 14. Although I instinctively tend to think of this as burning-in, because overall it makes the faces look darker, it really is unlike ordinary burning-in. Most of the tones are darkened, it’s true, but the near-whites are substantially brightened because I dragged the white point in from a value of 255 to 227. So, at the same time that I’m burning in the highlights, I’m also improving their contrast and preserving whites.

After another few minutes work, I had the mask shown in Figure 15 and the corrected photograph shown in Figure 16. The dodging and burning-in layers have completely corrected all the unevenness in the original photograph and enhanced highlight detail.

About the Author

Ctein is a technical writer and expert printmaker. He is also the author of Digital Restoration and Post Exposure—Advanced Techniques for the Photographic Printer.