[mtripoli]

Leveling in PS is almost mandatory on most images I have (rendered or photographs)... I have been doing this using the "RGB" channel. I just read about an "advanced" technique in which you level each RGB channel individually... my tests come out with too much green (in this case).. of course I can adjust it by eye...

The question is, how do you do it? RGB together, seperatley?

[vansan]

I use Phototune 2020 Color MD v2.0 plugin. It's good one, try it

[mtripoli]

Thanks for the input... I have Bibble Pro which is a fantastic program for making any adjustements... I'm more interested in the mechanics of doing this "under the hood"...

[noseman]

my rule is, work with 48bit images on a colour calibrated workflow and use any tools that makes your image look good to you (and your clients).

[RonB]

I am not sure exactly what you are discussing here, adjusting just gamma or color correction? I am thinking color correction and will comment from that point of view.

First off, color correction in Levels is not advised, a much more powerful tool for color correction is Curves, done in each color channel. An even more powerful combination is changing the color space to LAB and using curves in the color channels of LAB. An interesting note is that Photoshop "thinks" in LAB...all of the internal calcs in Photoshop are done in LAB. Lab is also a great stepping stone when changing color spaces...in going from RGB to CMYK for print, always go: RGB - LAB - CMYK. Color correction and sharpening are good in LAB because LAB is the only color space that seprates the detail of an image from the color information. Although LAB is a 3 channel space it's actually a 5 "color" space. Channel 1 (L) carries the grayscale or lightness detail and no color information. Channel 2 (a) carries the Red and Green information and no detail. Channel 3 (b) carries the Yellow and Blue information and no detail. Lab is also an exponential color space so when making adjustments a slight move in Curves gets a radical color shift. But once you get comfortable using Lab you will find it's very, very handy.

Something to remember is that color adjustments in Curves or Levels is really only shifting the tones right or left in the histogram and everytime you click, O.K., you are degrading the image. Open a clean, (a PSD not a JPEG, JPEGs are already degraded), image that has not been messed with and take a look at the histogram in Levels , make an adjustment and hit O.K., reopen the image in Levels and look at the histogram again...you will see it now looks like a comb. Those blank spaces in the histogram are where the tones were spread out and are now missing.

Another tool that I use regularly for color correction and one that will actually add or subtract information in the color channels is Selective Color. Found in Image/Adjustments/Selective Color. You can adjust specific colors within an image without making a selection to isolate the color. Sometime you might need to make a selection but generally you don't have to. Its a very powerful tool and will not degrade the image because in stead of shifting tones in the image like Levels or Curves, it actually adds or takes away color information from the Channels.
Be sure sure you click the Absolute button when you open the tool...I think it defaults to Relative...Absolute is better.

Another thing when doing color correction, especially for print is...never, never trust your monitor, never color correct by eye...unless it's just for you. Always, always color correct by the numbers and know what numbers you are going for...

I saw a very impressive demonstration of that once at a seminar. An instructor spent 1/2 an hour teaching someone color correction in Curves by the numbers, that had never used Photoshop before, and then gave them an image to color correct for print. The resulting image looked great when printed on the color proofer...the kicker was the person was totally color blind!

Cheers, Ron

[mtripoli]

Hi RonB,

Thanks very much for the info. You in fact hit upon exactly what I am reading right now... I got a couple of books over the weekend concerning this. They suggest doing color correction exactly as you say. I was looking at one example where they did it using the level tools... I was curious to how well it worked... they also recommend doing everything with curves... sooooo... I will begin learning this as my workflow...

Thanks very much for the input!

[jdp]

wow! thanks very much RonB, I always wondered how a correct workflow was... very instructive!

[mrcharles]

mtripoli...

I might suggest (if you are using photoshop) that you also try...

1: Create a Levels adjustment layer

2: Use the "middle gray" dropper to click on pixels in the image that should be neutral gray... sometimes this takes multiple clicks.

3: Adjust the intensity of the color correction by varying the opacity of the adjustment layer (top right of layer palette).

Note... this "mid-gray" dropper/sampler appears in other dialogs as well (eg. curves).

[mtripoli]

Thanks mrcharles... I'll give it a go...