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|| SportsShooter.com: News Item: Posted 2009-07-27

It's all in the Details
Max Out Dynamic Range with Gradient Masks

By Josh Lehrer

Photo by

On the left, the edit in camera raw that is ideal for the image with the exception of the blown out sky. On the right, the proper edit for a sky with detail.
As the mega-pixel race marches on, camera manufacturers constantly boast new claims of 15+ mega-pixels in sensors often not bigger than your average postage stamp. What has improved at a significantly slower rate is overall image quality; especially since the industry is quick to forget how bad things used to be and feverishly demands better and better technology.

I'll start by saying the single most important thing a photographer can do to get the best image quality possible is to shoot RAW. Without getting into a RAW versus JPEG argument (not this month anyway), shooting RAW is, without a doubt, the single easiest way to get the highest image quality from any digital camera, hands down. In situations dealing with mass amounts of images, RAW might not be practical, but rarely in those situations does one look for the absolute highest quality.

On the subject of dynamic range, the average sensor has about 7-9 stops of usable dynamic range. This is adequate for a studio shot or landscape on a cloudy day, but start introducing bright skies or deep, black shadows, and histograms soon hit a brick wall.

What is incredible about shooting RAW is the amount of detail captured that is unseen by simply processing the file once. While a sky might appear to be completely white, there is almost always detail to be saved. A digital image is composed of three channels, Red, Green, and Blue. If one of these channels registers as 255, which is pure white, the image will appear blown out. However, there is often hidden detail in the other channels, waiting to be brought out by re-processing the raw file.

In practice, this is quite easy. After processing the raw file to the ideal settings, open it in Photoshop. The overall image should look exactly as you want, ignoring the sky completely. Once that's done, open the raw file again into Adobe Camera Raw. In a scenario in which the sky is blown out, drag the "Exposure" slider to the left until you begin to see detail in the sky. Open the raw file again in Photoshop. Now there are two files open, the properly processed raw file, and a very dark version that has the perfect sky.

Combining these two files is where things get dicey, and highly image-dependent. The best tool for the job is a gradient mask. Using the properly exposed image as a background, click on the dark image with the "move" tool (shortcut is V) and hold down "shift." Holding the shift key assures the dark image is dropped exactly centered on the properly exposed image. Now drag the dark image on top of the properly exposed image. It's time to add a mask to the top layer, which is the dark image. While on that layer (it would be highlighted blue), click the "add layer mask" button on the bottom of the layers palette; it is to the left of the "adjustment layers" button.

Photo by

What an ideal final image might look like. The gradient has been placed on the mask, bringing back the detail in the sky that was once thought lost.
There is now a mask on the layer with the dark image. The fact that skies generally tend to have a natural gradient to them works in our favor in this case. First, the mask must be filled completely with black, hiding the dark image altogether. To do this, the paint bucket can be used, or use the shortcut "shift-delete" to bring up the "fill" dialogue while you are on the newly created mask, and select black. An even shorter method is to simply invert the all-white mask to all-black, by hitting apple-I (control-I on a PC) on the keyboard.

To create the mask necessary to finish this task, click on the "gradient" tool. If you don't see this tool, it is in the same family as the "paint bucket" and can be accessed with the G key. If you type G and get the paint bucket, type shift+G to get the gradient tool. Once the foreground/background colors are set to white and black, respectively, you are ready to bring back the previously over-exposed sky.

The gradient tool works by dragging a line across the image. The direction of the line indicates the direction of the gradient; in this case, we want to go straight up and down. Hold down the "shift" key to assure that the line is perfectly vertical. The length of the line indicates how quickly the gradient transitions from the foreground to background colors, in this case, white to black. The length of the line is determined by how quickly you want the sky to transition down the image. There is no rule that says the gradient must start or end within the image, you can zoom out of the image and start the gradient far above it in the "gray area" around the image itself in Photoshop. On this image, I end the gradient near where the sky meets the hills.

Playing around with the gradient is easy, since in its default mode, the gradient tool always over-writes the previously created gradient. No need to undo, just keep creating new gradients until you find one that works perfectly.

This technique requires practice and patience, but when used properly can do more than just bring back in blown-out skies. Use gradient masks to compensate for color shifts from different light sources in an image, such as tungsten on one side and daylight on the other. Or use it to gradually blur a background. I would encourage experimenting with this tool, remembering that with the power of layer masks, you are able to make unlimited changes to your image, and always go back to the original with a few clicks of the mouse.


(Josh Lehrer is a recent graduate from the advertising photography program at the Rochester Institute of Technology. He is currently working as a freelance photographer/assistant out of New York City; his work can be found at http://www.joshualehrer.com.)

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