Curves

[Nasturtium]

post your "stupid curve tricks" / everything you ever wanted to know about curves but where afraid to ask here.

I used to think there was some huge mystery to curves but it's just a matter of spending some time figuring out how they work.

Originally Posted by Der_W

Curves are based on the luminosity of the individual channels.
So if you're clicking on a lower point, you'll most likely select a portion of the channel that is at this level of luminosity.
The rest on going up or down is really color theory.
In RGB lightening the individual channel's curves will add more of that color, darkening them will add the complementary colors (Cyan, Magenta, Yellow). Raising the composite will brighten/darken the image overall.
In CMYK its the same, the only difference is that you maybe have to raise the curves in the opposite direction (prepress folks find it easier to think in terms of density than in terms of luminance levels).
LAB is the only color mode where you can and most certainly will use very crooked curves in the individual channels (to be more precise: in the a- and b-channel).

Think of it this way: Curves are the far more complex version of levels. They allow you to modify one point and fix an other one to a certain position so it won't be modified as well. Levels just have the black-, white- and middle point for each channel.

from this thread

Solar curve for retouching thread

changing tone thread

Jacob's Ladder.

feel free to link to other useful threads. There were two that showed some neat tricks with the blue and red channels for cross processing but I haven't relocated them yet.

Enjoy!

- Nancy

[Der_W]

Great idea :-)
Thanks for quoting my post!


I sometimes use arbitrary curves in LAB to get rid of one color all together.

E.g. change color mode to LAB then open up the curves dialog.
Click on the little pencil and go to the channel which contains the color you want to neutralize (a for the Green/Magenta, b for the Blue/Yellow).
Now here comes the trick :-). If you want to eliminate green, switch to the a channel, use the pencil to click on the point 0/-128, shift click on 0/0.

Every shade of green (LAB green looks more like turquoise just in case you're wondering) should turn gray/lose its green shade.
Very useful for restoration work sometimes :-).



Solar curves and the ladder are great examples of curves as well, I love to do both techniques :-)

It's btw. a great idea to save some presets, e.g. neutralizing colors (like I just explained), fixing midpoints, neutralizing the whole image (for the ladder) and maybe some solar curves.


PS: It may be worth noticing, that moving the gamma slider in levels is not the same as moving the midpoint in curves.

[Nasturtium]

for posterity;

various way to achieve cross processing with curves

post #11
http://www.retouchpro.com/forums/pho...eve-color.html


and/or
http://www.retouchpro.com/forums/pho...-lighting.html

http://www.retouchpro.com/forums/pho...ur-change.html

http://www.retouchpro.com/forums/pho...ve-effect.html

http://www.retouchpro.com/forums/pho...-get-look.html

[mistermonday]

I have a whole set of Curves which replace Blend Modes. Often you duplicate a layer for an effect and you change its blend mode and then selectively apply the effect by working on the layer mask. Using a curve to perform the same function allows you to replace a full pixel layer with a curve which occupies virtually no memory and has negligable impact on file size and does not slow PS down.
Here is the process to create those curves.
Sample attached.
Regards, Murray