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2.3.8 Improving Shadows with a Histogram and Gradation
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After the improvements explained up to this point, the shadowed region under the bridge still looks far too dark. A comparison of the old photo with the scan preview shows that there are still lots of details visible in the photo. They should also be worked out in the scan, which can be done using the histogram and the gradation curve. First the relatively narrow shadowed area in the histogram is assigned a larger range of the color space. To do this, in the expert dialog, move the shadow offset further into the bright range. The structure of the masonry shows up in more detail, and the separating line between the water and the stone is now visible again. In the histogram, moreover, separately displayed color channels can also tweak the color cast removal just a little more. The highlighted, middle, and shadowed points shown in each color channel can be moved around with the mouse until the color balance looks right. SilverFast shows the histograms for the prescan by default, which stay the same despite all the changes made to the image. The histogram for the final scan is shown when you hold down the Alt key.
Another improvement to shadow reduction can be obtained by making changes on the gradation curve. In the expert dialog for the tool, move the slider for shadow a little into the negative range, reducing the shadow under the bridge. The glare can also be reduced a little to remove the overexposure from the brightly sunlit bridge pilings and highlight the structure of the masonry again. The changes make the image a little pale, i. e., low-contrast. So now we push the contrast slider into the positive range, while simultaneously carefully reducing the midtones. Excessive changes to these two sliders would make the shadow under the bridge too dark again. So be careful making these changes. 
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