RustyBug wrote:
At this rate, it'll be 2020 before I get "good". But, even though technology changes very rapidly and there are always new iterations around every corner ... color theory and value control is really the same as it has been for the last 10, 100, or 1,000 years, i.e. light & color don't change, only our tools for capturing & presenting them do. So, if it takes me another 10 years to get "command & control" of the tools ... I'll still have plenty of time to put them to good use.
So here we are in 2021 now. Do you feel you done got "good" at this stuff Kent?
It would be interesting to hear your thoughts on what you have learned in retrospect to your quest, nearly a decade later.
And yes, I'm still digging around in the dark cobb web infested corners of the internet looking for info such as found in this old thread.
Lighthound & Kent, In levels, sliding the end point sliders almost always throws away information. However, sometimes the area thrown out contains almost no data. If the histogram line is on the bottom of the levels dialog graph - you can slide the right slider to the very edge of where the graph starts heading up, because there is no data in that flat line. Same with the left end point (shadows) the pointer can be pulled to the very beginning of the graph that lifts off the bottom. Once you go past that left and right end point into the recorded data, or change the mid-tones - you throw away data. Levels is a crude and generally destructive way to quickly edit an 8bit (16bit?) image using three points. In curves you can define as many points of adjustment as you want. It is like levels on steroids. A simple rule with curves is to keep the shape of the adjustments like a gently curving snake stretched out. Dramatic adjustments close to each other on the adjustment line almost always are destructive. I never use levels. In both levels and curves if the image is opened again in photoshop, and a levels or curves adjustment is attempted again - the histogram quite often, will have vertical lines in it. Those are luminosity levels that were previously discarded on the first adjustment.
People are obsessed with going back on highly edited images - so they can supposedly save time and pick up where they left off. Other than for paths or masks - I never do this. The history brush and blending modes can save you a ton of time recovering shadow detail, or many other adjustments. Many of the things I learned in 1989 with photoshop 2 - I still do, because it is faster, and usually better.
Jim
RustyBug wrote:
I'd like to find a resource that can explain what the different functions of PS actually do numerically/mathematically.
For instance ... sliding the endpoints in levels adds/subtracts to the existing value.
There are Input and Output boxes in Curves (and something sort of similar in Levels although I never use that tool) and those boxes will give you an idea of what's going on numerically. For instance, when the Curves output box says 238, that happens when you're dragging the highlight end of the curve to the left (assuming you've got it in normal RGB orientation mode) and that would mean that the pixel value 238 is now going to be 255. The Info Palette is more informative because it'll you the before and after value of any pixel anywhere in the image.
Really, all Levels or Curves is doing is altering the pixel value of any given pixel, groups of pixels or range up or down but, depending on how you manipulate the interface that value change could be linear or not. Doesn't really matter for artistic images but might for some scientific studies.
You can put up to 16 adjustment points on each of the four curves in the RGB curves dialog (there would be five potential curves in CMYK) It's not unlimited but sixteen is usually more than enough. Levels is a bit more complicated as there are only three adjustable points but you cannot address things like crossover colors in Levels because of the control limitations. Also in Levels there are actually five points in the adjustment interface but two of them are invisible and you have no control over them. They are lock down points near the white and black points but not at the very tonal limits. They are there to help prevent overzealous Levels users from ruining their images with super harsh adjustments and effectively limit the amount of the adjustment in the extreme shadows and highlights. Probably a good thing as the less advanced users tend to use Levels over Curves. For some reason they find Levels more comforting I guess. You can accomplish the same thing in Curves by adding a couple of points to the Curve but I rarely so that as it's seldom necessary.
lighthound wrote:
So here we are in 2021 now. Do you feel you done got "good" at this stuff Kent?
It would be interesting to hear your thoughts on what you have learned in retrospect to your quest, nearly a decade later.
And yes, I'm still digging around in the dark cobb web infested corners of the internet looking for info such as found in this old thread.
You're late ... what took you so long? 2020 was last year ... oh, yeah the year that everybody wanted to forget. Guess I forgot about this thread, too.
Retrospective, well ...
Whoa ... let's just say that back then 2020 seemed like a long way off. I guess it means I'm an even slower learner than I thought I was.
At this pace, I guess we should make hotel reservations for the upcoming eclipse.
I still can't say I'm "good" ... too many other folks way better than me. But, I'd like to think I'm better than I was back in 2012.
That, or maybe I'm just finding more things that I'm "not good" at, and working on makin' them a bit better. I still seem to be me, for all the good, bad and ugly that comes with that ... except maybe a bit more heavy on the ugly mug side if things.
BTW, I never did find that mathematical reference for the various operators ... but, then again, I haven't looked that hard lately, either.
Some of it is in the curves dialog. Here is an example ctlr + M look for the three eyedroppers, close curves. Move your eyedropper tool over some part of the image you want another part to match exactly. Write down the RGB numbers. Ctlr + M again & double click the gray eyedropper. Type those numbers in the curves dialog box. It will ask if you want to make them the default - go ahead and say yes or no. Now take the same eyedropper tool outside the dialog and single click it on the image exactly where you want that color. It changes color - click ok. Back in the main PS window click on the history tab, and select the prior state before the curves change. In the history palette put a tic in the box on the far left where the change was applied. Usually immediately below the prior state. Now pick the history brush from the tool palette and a soft brush. Paint the color change in the area you want.
Too involved? Here are simple global color corrections. ctrl + M click the gray eyedropper and click on the photo something that is approximately 20% gray. The whole image will change. You can do the same with the white or black eyedroppers. Lets say the blacks have a red cast - do the above with the black eyedropper - then use the history brush to just change the blacks, or let it be a global change.
RustyBug wrote:
BTW, I never did find that mathematical reference for the various operators ... but, then again, I haven't looked that hard lately, either.
James Markus wrote:
Some of it is in the curves dialog. Here is an example ctlr + M look for the three eyedroppers, close curves. Move your eyedropper tool over some part of the image you want another part to match exactly. Write down the RGB numbers. Ctlr + M again & double click the gray eyedropper. Type those numbers in the curves dialog box. It will ask if you want to make them the default - go ahead and say yes or no. Now take the same eyedropper tool outside the dialog and single click it on the image exactly where you want that color. It changes color - click ok. Back in the main PS window click on the history tab, and select the prior state before the curves change. In the history palette put a tic in the box on the far left where the change was applied. Usually immediately below the prior state. Now pick the history brush from the tool palette and a soft brush. Paint the color change in the area you want.
Too involved? Here are simple global color corrections. ctrl + M click the gray eyedropper and click on the photo something that is approximately 20% gray. The whole image will change. You can do the same with the white or black eyedroppers. Lets say the blacks have a red cast - do the above with the black eyedropper - then use the history brush to just change the blacks, or let it be a global change.
What I'm actually looking for is the mathematical formula that the operators use for computation.
Each operator (blend mode) has a very specific formula it uses. I've seen them before, but they were "over my head" when I originally saw them. I've since come to understand how they work, but I can't seem to recall where to find the list of all the different blend mode formulas.
I know that it may sound very odd to want to see the math. My reason for the interest is so that I can understand which operators are using exponential operations, vs. which ones are using linear operators etc. Some are more "powerful", others are more "refined". Some apply to the entire range, while others have constraints built into their range.
Just would like to know the math operations to compare what is actually being done with the 0-1 or 0-255 values.
