1/20/2024 0 Comments Gimp photoshop levels![]() ![]() However, it doesn't work perfectly: you'll lose some information to rounding errors every time you make a change. Theoretically, you could reverse a change of gamma=2 by applying a change of gamma=0.5. (New value / 255) = (Old value / 255)^(gamma)īecause 0 to the power of any number is still 0, and 1 to the power of any number is still 1, the extreme brights and darks of your image aren't changed by gamma correction, while pixels that have medium brightness are changed the most. So, for example, the opposite of a 1.5 value is 1/1.5 = 0.67. In general, a gamma value of x (greater than one) is the same magnitude of change as a value of 1/ x. So a value of 2 works by "squaring" the values (after scaling them to the range 0-1), while a value of 0.5 (=1/2) works by applying a square root to the scaled value. ![]() So if you pick a bluish-grey pixel, it will reduce the gamma on the blue channel and increase it on the red and green channels so that the new colour for that pixel has the same brightness, but is a perfectly neutral grey. The "grey point" that you pick using the eye-dropper button in the All Channels section works by adjusting the gamma values for the red, blue, and green channels separately, without changing the overall gamma number for the image. You can set it for the value channel (applying to all colours equally) or for each colour channel separately. The middle value on the Input slider at the top of the dialog is called the gamma number or gamma correction number. The longer answer requires first some definitions. The short answer is that the difference from 1.00 to 2.00 is the same as the difference from 1.00 to 0.50 (i.e., from 1 to 1/2). But what value I should use to make the same amount of adjustment (just to other side) as when I move the slider from 1.00 to 2.00? If I move it to the right, the picture become darker. If I move it to the left to value 2.00 (from 1.00) the picture become lighter. In levels I can move the grey point on scale from 0.10 to 10.00 with 1.00 in the middle. ![]()
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