Correcting daytime black sky

The gradient tool is the answer.

Sometimes, you will take a picture of a scene with a beautiful blue sky that has a part of the sky overly dark, even black. This is usually due to the use of a polarizing filter, and can be exacerbated by underexposure. You can avoid it when taking the picture by setting your polarizing filter so that the sky doesn't become too dark.

An area of your image may be darker (or lighter) for other reasons, including, for example, lens flare, or accidentally blocking part of the scene by an object near the front of the lens, like a finger.

A very dark area in an otherwise blue sky looks unnatural, and should be avoided when possible. But, what if you have already taken the picture? Can it be fixed in the digital darkroom? The answer is decidedly, yes.

This sunny Las Vegas sky (right) has its upper left corner rendered as black, gradually lightening to a more natural blue towards the center of the scene.

Correcting the image means eliminating the dark sky in a gradual manner so that it looks normal. Adobe PhotoShop and other image-editing software have just the tool for the job. It is called the Gradient Tool.

The Gradient tool allows you to remove the black gradient without affecting the rest of the picture.

Here are the steps that were taken to correct the Las Vegas sky picture above.

1. The Gradient tool was selected by clicking on it.
2. The Linear gradient option (the tool icon shown at left) was selected in the options bar. There are a number of different gradient tool options, each with its own icon and its own method of gradating. The Linear gradient option shades from the starting point to the ending point in a straight line.
3. A clear (transparent) background gradient fill option was chosen from the options bar.

4. Because blackness was to be reduced, black (the default setting) was chosen as the foreground color.
5. You fill an area with a gradient by dragging in the image. The starting point (where the mouse is pressed) and ending point (where the mouse is released) affect the gradient appearance, depending on the Gradient tool option chosen.
6. Our starting point was the corner, the area of deepest darkness. We dragged the cursor towards the lighter area of the picture, releasing it near the center.
7. We experimented a few times, and ended up making two passes, adjusting the opacity to 55% for the second pass, and finally got it just right.

If this sounds difficult, it is not. You just need to try it a few times to become familiar with the results from small changes you make. Practice and you will soon get the knack.

Using the Gradient tool successfully altered the sky. It now has a more natural appearance, a significant improvement on the original image.

The Gradient tool is handy in correcting more than just dark skies. It is useful for just about any problem where tonal gradation needs adjustment.

For more info on Photoshop's image-editing tools, see Toolbox for image-editing.