Gamma correction and levels adjust instead of brightness and contrast

Gamma correction and levels adjust

Correct your photos that are too dark or too light easily

Levels adjust combined with gamma correction is a different approach than the standard brightness and contrast correction. I would say it is much easier and gives much better results faster.

So what is wrong with brightness/contrast correction?
Both functions may quickly push some areas of your photo out of range. That means a part of your photo that was not over-exposed before the correction will be after the correction (it will be completely white, all nuances lost).

The same is true for dark parts that may get under exposed i.e. completely black, all nuances lost.

Another problem with common brightness/contrast correction is that you will mostly try forth and back many times and still not get the best results.

Applying a gamma correction instead of a brightness correction, you will never propulse some part of your photo into the over-exposed (under-exposed) zone if it has not been there before. White will still be white, black will still be black and everything between will just be pushed upwards or downwards but not out of range.

A gamma correction of 1 means no changes.
A gamma correction of 0.1 to 0.99 means a darker image.
A gamma correction of 1.1 to 5.0 means a lighter image.

ATTENTION: I have seen occasionally that some software use a reverse logic! below 1 is lighter, above 1 is darker!

After applying a gamma correction ONLY, your picture that was too dark has become lighter, but it may look like washed out. You may feel it needs more contrast.

This is why you need a levels adjust instead of only a gamma correction. The levels adjust of Photo-Brush is in deed a gamma correction where you additionally pull the dark parts towards black and the light parts towards white.

If this seems too complicated, just think about levels adjust as 3 cursors to move:

if the histogram is flat at the left, move the left cursor to the position where the histogram curves start (e.g. 6 or 10 or 20...)

if the histogram is flat at the right, move the right cursor to the position where the histogram curves end (e.g. 200 or 220 or 240...)

if the mid-range colors are still too dark, move the central cursor to the left (e.g. 1.2 or 1.4 or 2.0...)

if the mid-range colors are still too light, move the central cursor to the right (e.g. 0.9 or 0.8 or 0.6...)

Example:

before	after

In the example above, we did only move 2 cursors:

the histogram being not flat at the left, we did not move the left cursor

the histogram being flat at the right, we did move the right cursor to the position where the histogram becomes flat (228)

to light up the mid-range, we did move the central cursor to the left (1.4)

Unfortunately, most image and photo editors still stick to the brightness/contrast concept. With this -obsolete- concept, -let me say it again- you will quickly create an over-exposed or under-exposed image. And you will miss any feeling concerning the correction numbers to apply, thus trying forth and back again and again.

Some image editors call it brightness/contrast, but in deed, what they do is a gamma correction/contrast combination. But without histogram, you will have to guess about the numbers.

Some have quite the same levels adjust as described and call it light/mid range/shadow correction. But without histogram, it is still a guess work.

About auto levels adjust:

I have seen some photo editors offering auto levels adjust, but in most cases (I mean with most photos I did apply the auto correction to) I was not satisfied with the result. I found the contrast of the result very hard and many nuances had disappeared.

The solution could be to have one value -that you define once- to choose how strong you would like the auto correction to be. The objection may be that it is not automatic if you have to choose a setting ;-)

Conclusion:

You need two things:

An indication telling you how much you should correct. This is the small histogram we mentioned above.

A feedback showing what is the real effect of the correction you are applying. This is given either by a small copy of your photo located in the dialog box where you set the correction values or better, by the fact that your photo is changing -live- behind the dialog box while you move the correction cursors.

Photo-Brush combines levels adjust with gamma correction displays a small histogram and lets you see the effects of your correction immediatly on the photo behind the dialog box.