Level Enhancement

Below are two mirrored images before (left) & after Level adjustment. The top one was done manually, the bottom using Auto-levels. Cover one side, then the other to see if you think this is a worthwhile technique to learn:

• Many images (in fact almost all images) can benefit from having their “Levels” adjusted
• If you have an image in Photoshop, always try this (you can always undo…).
• Be careful not to overdo it!
• Level adjustment is a more sophisticated way to change brightness and contrast, allowing you to adjust, dark, light and mid-tones separately.

There are two methods, both under the Enhance menu:

1. Auto-Levels. Quick and easy, often very successful, but sometimes goes too far, or gives effects you don’t want, such as hue shifts and washouts
2. Manual Adjustment using histogram and sliders. (Enhance menu => Brightness & Contrast => Levels (Ctrl-L))

Auto-Levels is self-explanatory – just try it. Again, be prepared to undo. Examine the image for overall effect, and areas that are washed out (skin, clouds & other light areas often lose important detail). If you don’t love what you see, undo and try the manual approach!

Manual level adjustment is something you have to experiment with to learn. Below are a few examples which show some common changes and mistakes. Load a few images and try it out. Again, examine the results carefully before committing.

This is most of what you see in the manual Levels window. The histogram (graph) shows the distribution of values. The original image (below left) has a predominance of dark (low) values, a lot of mid values, and very few high (bright) values. The 3 sliders adjust the brightness levels of the low, mid and high value pixels. You can also adjust Output levels, and restrict the changes to certain colours (channels) rather than the whole RGB spectrum.

		The black slider controls the darkest pixels. Moving it slightly right to the beginning of the value curve darkens the picture but adds contrast. The white slider was moved left, brightening the image. Since there are very few high-value pixels, this didn’t wash any light areas out. The middle slider controls the mid-value pixels, and usually is best about half-way between the other sliders.
Original image – not vivid	After applying the levels shown at right – subtly better.
		The white slider has been moved too far to the left, resulting in washout.
Auto-Levels did a pretty good job, but gave a greenish cast	At a glance, the result of this manual level change looks good, but it’s too bright in parts. Note the washed out detail on the rocks