Gamma vs brightness vs highlights/shadows

teddoman

Regular
Location
nyc
How do folks decide when to use a gamma slider vs a brightness slider vs the highlights/shadows slider? They may go by slightly different names in different PP programs.

I read up on gamma a bit. So if system gamma = 1 is standard, then changing gamma seems to shift the brightness of an image but it does so by changing the shape and location of the gamma curve.

Whereas a brightness slider probably just changes the luminance of the image in a fixed linear fashion.

If you have highlights and shadows sliders, then you're only adjusting the bright tones or the dark tones of the image respectively. So using highlights and shadows sliders seems intuitive to me. Sometimes you just want to pull back the highlights or bring up the shadows.

But when do you decide to adjust gamma as opposed to brightness? From what I can see (and guess), it's a curved adjustment as opposed to a linear adjustment. Is there a difference in practice?
 

Luckypenguin

Hall of Famer
Location
Brisbane, Australia
Real Name
Nic
In Lightroom, all of the 5 sliders to adjust brightness (blacks, shadows, exposure, highlights and whites) are weighted towards a particular section of the histogram. They are like a non-graphical way to make curve adjustments.
 

Richard

All-Pro
Location
Marlow, UK
I think for photo-editing purposes, all of these controls are just a means to an end, which is to allow you to manipulate the range of tones within your image by adjusting the transfer characteristic between input and output values. Sometimes it's more convenient/effective to do that by introducing an overall curvature to the graph by adjusting gamma, and sometimes it's more convenient/effective to play with highlights or shadows, and so on.

Gamma correction has an interesting technical history relating to the linearity (or otherwise) of TV cameras and monitors, but you don't need to know all that when you're just playing with the Lightroom sliders to make the image look the way you want.

-R
 

teddoman

Regular
Location
nyc
Part of the reason I wanted to understand how gamma works is that I noticed that using the gamma slider has an effect on brightness but so do a lot of other sliders. I didn't want to increase brightness with one slider and then reduce brightness with another slider. Understanding the precise effect of each slider would give me a bit more control over achieving something that looks good. it's kind of like, you could futz around with all the dials on your camera until you get something that looks right, or you could just learn the exposure triangle and understand how they all interact.
 

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