How to accurately crop dark-edged images in Photoshop
by Chris Nicholson

When scanning transparencies full-frame into Photoshop, it's good practice to leave a little room around the edges of the image to ensure that the scanner doesn't inadvertently ignore some data. Then, one of the first adjustments you'll need to make is to crop the dark edges off the image. That can be tricky with a photo that has abundant dark areas, especially silhouettes. But an easy way around this problem is achieved using Adjustment Layers.

Figure 1 (below) is a perfect example of this problem. All the black on the bottom of this un-cropped photo makes it difficult to discern where the lower edge of the image is, and, therefore, where to crop.

First, click the "Create new fill or adjustment layer" button on the Layers Palette, and select Levels from the menu. (If you're using an older version of PhotoShop, ensure that the image is in 8-bit mode, so you can add an Adjustment Layer.) Locate the upper right slider (circled in red in Figure 2).

Click on that slider and drag it as far to the left as you can. The third "Input Level" (the one for the white point) should read "2" (see Figure 3).

This will make all the darkest parts of the image change to much lighter shades or to white. Because the outer edges of the image are really just the pure-black outsides of a slide mount, they'll remain the darkest areas of the image, allowing you to easily see where to crop. Click OK, and the image will look like Figure 4.

Using the crop tool, set the crop lines to just inside the dark edges of the image (Figure 5).

Press Enter on your keyboard to complete the crop. Next, in the Layers Palette, select the Levels layer that you created at the beginning. Then click the "Delete Layer" button on the palette, and click Discard in the dialog. Now you have an image perfectly cropped to the dark edges of the photo (Figure 6).

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