Selectively Improve Exposure

If digital cameras had the exposure latitude of the human eye, it would be downright miraculous. Part of the art and science of photography is accounting for the fact that cameras have only about half the range. So something that looks breathtaking in person often looks under- or overexposed when captured by a camera.

There are some fancy technological workarounds to this problem. Ulead PhotoImpact 12, for example, has a "high dynamic range" feature that lets you combine several pictures of the same scene, taken with different exposures, to automatically achieve a photo that pops with highs, lows, and everything in between.

This week, though, let's see how to improve photos that suffer from exposure problems, using just your favorite editing program. As usual, I'll use Corel's Paint Shop Pro, and you can apply this technique to almost any program.

Don't Adjust the Whole Photo

Sometimes you don't want to apply an exposure correction to the entire image. Take this photo, for example.

You might be tempted to fix the image by using the histogram to lighten the parts of the image that are in shadow--and that is a quick-and-dirty way to go. In Paint Shop Pro, choose Adjust, Brightness and Contrast, Histogram Adjustment. You should see a histogram graph that's heavily weighted to the left, which means the image has a lot of dark pixels, and few bright ones.

To brighten the image, drag the white triangle that's on the far right under the histogram towards the left until the number in the box at bottom right is at about 15.000.

That's better in some ways. Notice how we've restored a lot of detail to the shadows. But we also overexposed the sky in the process, making the clouds so bright they almost hurt the eyes. There's a better way. Click Edit, Undo and let's try again.

Select Just the Sky

Instead of brightening the entire image, let's focus on the underexposed section. To do that, select the Freehand Selection tool from the third cubby on the toolbar on the left side of the screen, and then choose Smart Edge from the Selection Type menu in the Tool Options palette atop the screen. (If the Tool Options palette isn't on screen, choose View, Palettes, Tool Options.)

Now carefully select the sky by clicking along the mountain ridge a little at a time, then working your way around the sides and top of the photo. Double-click when you get back to your starting point. If you make a mistake, right-click to start the selection over. Don't bother trying to cut around the three trees on the left that jut into the sky; just keep following the contour of the mountain.

Once the entire sky is selected, choose Selections, Invert. This "flips" the selection so the sky is the only part of the scene that isn't selected. Clever, no?

Try the Histogram Again

Now you can reapply the histogram, using the same settings we tried at the beginning of the task. How does it look?

It's possible that you ended up with an ugly, overexposed seam along the ridgeline. That's because the selection includes the edge of the trees, which have little bits of sky mixed in. To fix this problem, undo the histogram adjustment and choose Selections, Modify, Contract. Set the tool to about 5 pixels and click OK (if necessary, you can use other selection tools to recapture the sides and bottom of the photo). Finally, run the histogram adjustment one more time.

This is what I got as my final result--notice that we got all the detail in the mountain, but the sky remains the same.

If digital cameras had the exposure latitude of the human eye, it would be downright miraculous. Part of the art and science of photography is accounting for the fact that cameras have only about half the range. So something that looks breathtaking in person often looks under- or overexposed when captured by a camera.

There are some fancy technological workarounds to this problem. Ulead PhotoImpact 12, for example, has a "high dynamic range" feature that lets you combine several pictures of the same scene, taken with different exposures, to automatically achieve a photo that pops with highs, lows, and everything in between.

This week, though, let's see how to improve photos that suffer from exposure problems, using just your favorite editing program. As usual, I'll use Corel's Paint Shop Pro, and you can apply this technique to almost any program.

Sometimes you don't want to apply an exposure correction to the entire image. Take this photo, for example.

You might be tempted to fix the image by using the histogram to lighten the parts of the image that are in shadow--and that is a quick-and-dirty way to go. In Paint Shop Pro, choose Adjust, Brightness and Contrast, Histogram Adjustment. You should see a histogram graph that's heavily weighted to the left, which means the image has a lot of dark pixels, and few bright ones.

To brighten the image, drag the white triangle that's on the far right under the histogram towards the left until the number in the box at bottom right is at about 15.000.

That's better in some ways. Notice how we've restored a lot of detail to the shadows. But we also overexposed the sky in the process, making the clouds so bright they almost hurt the eyes. There's a better way. Click Edit, Undo and let's try again.

Instead of brightening the entire image, let's focus on the underexposed section. To do that, select the Freehand Selection tool from the third cubby on the toolbar on the left side of the screen, and then choose Smart Edge from the Selection Type menu in the Tool Options palette atop the screen. (If the Tool Options palette isn't on screen, choose View, Palettes, Tool Options.)

Now carefully select the sky by clicking along the mountain ridge a little at a time, then working your way around the sides and top of the photo. Double-click when you get back to your starting point. If you make a mistake, right-click to start the selection over. Don't bother trying to cut around the three trees on the left that jut into the sky; just keep following the contour of the mountain.

Once the entire sky is selected, choose Selections, Invert. This "flips" the selection so the sky is the only part of the scene that isn't selected. Clever, no?

Now you can reapply the histogram, using the same settings we tried at the beginning of the task. How does it look?

It's possible that you ended up with an ugly, overexposed seam along the ridgeline. That's because the selection includes the edge of the trees, which have little bits of sky mixed in. To fix this problem, undo the histogram adjustment and choose Selections, Modify, Contract. Set the tool to about 5 pixels and click OK (if necessary, you can use other selection tools to recapture the sides and bottom of the photo). Finally, run the histogram adjustment one more time.

This is what I got as my final result--notice that we got all the detail in the mountain, but the sky remains the same.