Brightness Transform

[Marpel]

I had an image that I was working on recently, in which the dynamic range, as shown in Levels and Colour, was (can't recall exact numbers but...) 30% and 60%.

Wishing to maintain the same dynamic range but brighten the image, I merely moved the Brightness slider to the right.

Once complete, however, the dynamic range was not the same 30% difference (quite a bit different, actually) between the lightest and darkest points. As I was not nearing either clipping point, is there a reason why the difference between lightest and darkest tones would not remain static?

Marv

[jsachs]

The dynamic range in Levels and Color is approximate since it does not work on the lightest and darkest pixels. If it worked that way, a single white or black pixel, while likely invisible in the image would set the white or black points. Instead, it averages the brightness of the brightest 0.01% and the darkest 0.01% of the pixels to locate the white and black points. When you adjust the brightness, this can change their values although usually not by much.

[Marpel]

Jonathan,

Thanks for the explanation.

Out of curiosity, I found the image that spawned my post and ran it through the Brightness transform again, whilst recording the numbers.

Start - DR 37.3 and 74.9 (difference of 37.6).

Moved Brightness slider to 76.3% and DR numbers now 78.4 and 96.9 (difference of 18.5).

Just thought the difference was worthy of an explanation.

Thanks again,

Marv

[jsachs]

If you can email me the image, I can take a look at it.

You can get better control over the dynamic range and brightness using Adjust instead of Levels and Color as it uses a curve instead of sliders.