Levels and Curves

[stargazerlily]

Hi Everyone,

I'm just starting out on Wide Field photography but I'm a bit (= lot) confused on the post processing side of things. I've read many threads about post processing and people talk about using Levels and Curves.

I have a vague idea what happens when applying Levels and Curves as I'm 'processing' my photos in GIMP. But I don't fully understand the 'why'.

i) What exactly are we trying to achieve when using Levels (and Curves)?

ii) Are Levels and Curves different, and if so what does each one focus on?

iii) What are we looking for when applying Levels and Curves to an image?

I appreciate that the answers to these common questions are probably within some tutorial or thread somewhere, but I've not been able to find the 'fountain or wisdom' when searching the site.

Many thanks for your help

Pete

[3ggman]

This is a good tutorial from Anna Morris, it uses photoshop but it will give you an idea of why use levels and curves and what it does.

[3ggman]

Forgot the link http://www.eprisephoto.com/basics-new

[stargazerlily]

Thank you for the link. Great videos.

I've done some background reading and I'm a little wiser ...

Cheers

Pete

[AstroTux]

With the GIMP levels allows you to set the lightest and darkest that a particular colour channel ( eg. Red ) should be.

Curves give you a lot more control. The secret of curves is to do with the histogram. Darker shades of the colour channel are shown to the left whilst the lightest shades of that colour are at the right hand side and their height indicates their intensity. By adding a point on the curve and then moving that point up and down you can then increase or decrease the intensity of that particular shade, and those around it if you are using smoothed curves. I find this technique particularly useful in normal photography to just raise the greens in a forest by the slightest amount, making the image seem less dull.

I probably haven't explained this as well as I could, but I hope it helps,

Alan