What is luminance? - DPChallenge Forums

Sigma 18-200mm f/3.5-6.3 DC OS for Nikon

04/18/2007 02:27:21 AM · #1

For all those experts out there. What exactly is 'luminance'?

What does it mean in terms of photography?
What does it mean in terms of PS layers?
What does it mean in terms of HDR?

Basically; when I read, '...in order to preserve luminance...', what is the author saying?

Greetmir

Nikon D60

04/18/2007 03:35:01 AM · #2

luminance

noun

Definition:

1. quality of being luminous: the condition or quality of emitting or reflecting light.
Symbol L

2. measure of brightness: a measure of the brightness of a surface, equal to the amount of luminous flux arriving at, passing through, or leaving a unit area of surface. It is measured in candelas per square meter.

Also called luminosity.

[Late 19th century. < luminant "luminous" < Latin luminant-, present participle of luminare "illuminate" < lumin- "light"]

Basically, I have had no problems understanding "luminance" if I just translate it to "brightness".

Message edited by author 2007-04-18 03:35:56.

04/18/2007 03:40:11 AM · #3

Thanks. So; the stuff on the histogram then?

But what does it mean in photoshop to blend a layer in while preserving luminosity? Or, what is the impact to add a curve layer in the luminosity mode? etc.

Canon EF 70-200mm f/2.8L IS USM

04/18/2007 06:02:50 AM · #4

bumpity-bump.

skylercall

Canon EOS-7D

04/18/2007 06:43:29 AM · #5

I too am wishing someone could answer this in detail (bump).

yanko

Canon EOS-5D Mark II

Carl Zeiss 50mm ZE f/1.4 Planar T for Canon

04/18/2007 06:53:07 AM · #6

Originally posted by Greetmir:

2. measure of brightness...

Basically, I have had no problems understanding "luminance" if I just translate it to "brightness".

Bingo. To understand it better in terms of Photoshop change the color space to LAB (i.e. Image/Mode/Lab Color). That color space isolates the luminosity from the color. You can see how this looks when viewing the channels. In LAB there is a Luminosity channel (L) and two color channels (A & B). If you wanted to edit the luminosity or just the color and not the luminosity working in LAB would be a good choice.