Mark Laubenheimer wrote:
i use raw files with lightroom.

Lightroom/ACR has curves adjustments too ya know.

Kaouthia wrote:
Curves lets you add a whole bunch of points (I think up to 8), so you can adjust the shadows differently to the midtones differently to the highlights, as well as your black & white adjustment points, and you can do this for each of the different colour channels.

Ahhhhhhh! Excellent! That makes GOOD sense! Thank you!

Ruben Vasquez wrote:
Among the most common uses of curves is to increase contrast with an "S" curve which can be done at pretty much any tonal range (quarter tones, midtones, three quarter tones, etc). At best, you can produce a "Z" curve in levels but you'll clip your highlights and/or shadows.

Another major advantage curves has is that you can color correct an image. Anything in the image that is supposed to be black, white or any shade of grey in between can be neutralized to exactly that with curves or in other words, the red, green and blue channels can all be made to equal one another at any tonal point. Moreover, you can add or subtract colors at any tonal point. Have a blue cast in the shadows you want to get rid of? Select the blue channel and lower the affected tones, add additional anchor points for tones you don't want to affect.

I'm sold! They just skipped across the top of all this at the seminar!
Much appreciated folks! Time to learn curves, and all advice and opinions are welcome!

Kaouthia wrote:

Lightroom/ACR has curves adjustments too ya know.

Lacks blending modes and opacity... I use curves in Luminosity a lot for contrast...

ACPhotography wrote:
Lacks blending modes and opacity... I use curves in Luminosity a lot for contrast...

I know, it wasn't an argument for LR over Photoshop, but he said he said he used LR (implying he doesn't use either levels or curves), and I replied before he actually posted the screenshot showing the curve in there.

I'm the same btw, using it as a "Normal" adjustment layer tends to screw around with the saturation too much.

Don Garrett wrote:
I use both, but the explanation is very long. I'll just hit a couple of highlights. Curves redistributes tonality, and can lengthen the tonal RANGE. The problem is, with curves, one quickly "runs out of space" on the two ends of the histogram. It takes a fair amount of technique, and some time, to set up for an effective curves adjustment. The tone information from a single RAW conversion is insufficient to accomplish this set up. I ALWAYS convert every RAW image three times, one with the exposure slider left alone, and two with the exposure slider set to the two opposite extremes, ("over", and "underexposed" by two stops each). When one has created a single image, with all of the tonal information bunched up in the middle of the histogram, (a flat image), there is plenty of room to make curves tone adjustments in both directions. Of course, the image straight out of the camera is necessary to complete the image, and the final product should have one, or a handful of pure white pixels, and one or a handful of pure black pixels, (but NO clumps of either).
  The end result is a single image that spans the whole range, (0 to 255), has NO  haziness, better shadow detail, and more "body" and apparent detail in the highlit areas, AND shows MUCH more "local contrast".
  I also use the program, Photomatix in this process. Curves is a very important, pivotal part of the process, but only a fraction of the whole story.

Great post Don! Good stuff! All good info on this thread!

ArtisticGlamour wrote:
Great post Don! Good stuff! All good info on this thread!

Thanks, but, Unfortunately there is a lot more to the story than this. What I was hoping for is that I stimulated some investigation into the secrets of Photoshop, and how to use the tools there to uncover them. It took me years, and the program Photomatix, to get the control I was looking for.
  The problem was getting the desired amount of shadow and highlight details, (different in each image), along with LOTS of "local contrast", and a "punchy looking image" - all at the same time.
-Don

JAE Photography PA wrote:
Curves I use sometimes but it is a lot more complicated compared to levels.

It can be, but it doesn't have to be.  At its simplest it works exactly like levels.

You move the bottom left of the line across to the right to set your black point, you move the top right of the line across to the left to set your white point, then you create a point on the center and move it up and down to set your midpoint.

That's pretty much exactly what a levels adjustment does.

Toto Photo wrote:
Because of all the positive press (e.g. "Curves is powerful") I've tried repeatedly to master curves and failed each time. I suppose I'll have to go to lynda.com or youtube to take some tutorials, but until I can make the time to do that, I'll have to continue to use levels.

You'll have to try it, but the basic thing you have to understand about curves is that the diagonal line through the box, represents the total tonal range of your image, the top right hand corner represents white, (255), and the bottom left hand corner represents black, (0). Every point in between represents the rest of the values, getting brighter as one goes toward the top, and darker as one goes toward the bottom. If one moves any point up, that value gets brighter, if one moves any point down, the value that corresponds to that point gets darker. I use MANY "push points", and keep the curve very smooth, and continuous, otherwise, the image gets "posterization", or worse ! Like I said in my previous post, setting up for a curves adjustment gives you the room to make aggressive adjustments in either direction, without spiking up the right or left hand side of the histogram, creating large areas of pure black, and/or large areas of pure white. The rest depends on what you hope to accomplish, regarding tonal distribution, and could take a lot of time and experimentation to get everything under control to your satisfaction.
  I hope this helps, now the fun begins !
-Don

Don Garrett wrote:

You'll have to try it, but the basic thing you have to understand about curves is that the diagonal line through the box, represents the total tonal range of your image, the top right hand corner represents white, (255), and the bottom left hand corner represents black, (0). Every point in between represents the rest of the values, getting brighter as one goes toward the top, and darker as one goes toward the bottom. If one moves any point up, that value gets brighter, if one moves any point down, the value that corresponds to that point gets darker. I use MANY "push points", and keep the curve very smooth, and continuous, otherwise, the image gets "posterization", or worse ! Like I said in my previous post, setting up for a curves adjustment gives you the room to make aggressive adjustments in either direction, without spiking up the right or left hand side of the histogram, creating large areas of pure black, and/or large areas of pure white. The rest depends on what you hope to accomplish, regarding tonal distribution, and could take a lot of time and experimentation to get everything under control to your satisfaction.
  I hope this helps, now the fun begins !
-Don

Appreciate the info, don't want to hijack the thread, but just to show how lost I am, I find it difficult to know what is changing, is it a single luminance value because it sure seems like values up and down the chain are changing. Are you saying, if I've selected a luminance value of 137 (on a scale of 0-255) and I'm on the RGB screen, that every luminance value of red 137, every one of blue 137 and every one of green 137 gets changed and only that (137) luminance value changes?

Or to put it another way, I've bolded the terms nobody has been able to dumb down enough for me to get through my thick skull.

Toto Photo wrote:
that every luminance value of red 137, every one of blue 137 and every one of green 137 gets changed and only that (137) luminance value changes?

It's the overall luminance value of the pixel.

If you load an image and just completely desaturate it, that's the luminance value of each pixel in your image.  That's what it's looking at and affecting when you just do an overall adjustment of the combined histogram ("combined" meaning, all three RGB channels lumped together, not adjusting a single channel).

However, when you have your layer blending mode set to "Normal", just like increasing and decreasing light levels or exposure, it will decrease or increase your saturation as you make it brighter or darker.

If you set the layer blending mode to Luminosity, it will only affect the brightness level without touching the saturation.

Neither is an "always use this mode" way.  I tend to use Luminosity 99% of the time, but occasionally just having it as in Normal mode works fine.

Kaouthia wrote:

It's the overall luminance value of the pixel.

If you load an image and just completely desaturate it, that's the luminance value of each pixel in your image.  That's what it's looking at and affecting when you just do an overall adjustment of the combined histogram ("combined" meaning, all three RGB channels lumped together, not adjusting a single channel).

However, when you have your layer blending mode set to "Normal", just like increasing and decreasing light levels or exposure, it will decrease or increase your saturation as you make it brighter or darker.

If you set the layer blending mode to Luminosity, it will only affect the brightness level without touching the saturation.

Neither is an "always use this mode" way.  I tend to use Luminosity 99% of the time, but occasionally just having it as in Normal mode works fine.

One of the best tips I've ever read! Thanks! Just look at these two images - the first without curves correction, the second with curve correction on the green layer in luminosity mode - even in lo-res the difference is subtle but palpable. Thanks

https://www.modelmayhem.com/portfolio/pic/30587899

https://www.modelmayhem.com/portfolio/pic/30616966

TMA Photo and Retouch wrote:
I use levels to bring up the black levels in a linear kind of way...and then I use curves to do painting with light, skin color correction, and high-end digital makeup.

Its curves that are applied selectively that allow you to have high-end non-destructive quality.

what does that mean?

TMA Photo and Retouch wrote:
High end results are obtained by the use of Curves Adjustment Layers.  In regular retouching...the actual image is written upon...and the actual pixels are changed...and the changes are embedded into the original image itself.

Yeah, that's just "non destructive editing", not "high end retouching".

Non destructive editing can still be done badly.

Toto Photo wrote:

Appreciate the info, don't want to hijack the thread, but just to show how lost I am, I find it difficult to know what is changing, is it a single luminance value because it sure seems like values up and down the chain are changing. Are you saying, if I've selected a luminance value of 137 (on a scale of 0-255) and I'm on the RGB screen, that every luminance value of red 137, every one of blue 137 and every one of green 137 gets changed and only that (137) luminance value changes?

Or to put it another way, I've bolded the terms nobody has been able to dumb down enough for me to get through my thick skull.

I see that some answers have already come in on this point, but I have my own way of saying it, so I will. One CANNOT change just one value with curves, as the very nature of the tool "pulls" other values along with it. It would be impossible, (I think), to move just one point, without moving several along with it. Even when you have anchor points on both sides of the point you are moving, the curved line on the other side of the anchor point moves, as if the points are acting as fulcrums. The important thing is, that the curve be smooth, and have a purpose. The redistribution of tonality in an image is to give the image more contrast in any local area, and the end result should be an increase in the number of tones, and show better detail in the shadows and highlights, or the tools are not being used to their potential.
  The reason I set up for the curves adjustment with more than one conversion from the RAW, is so I have the room on the histogram to make the changes I desire before I spike the right or left side of the histogram, (make clump(s) of pure white, or pure black pixels). Absolute control of the tonality, an increase in the number of tones, better shadows and highlights, and much more local contrast, are all possible with understanding and "proper" use of the tools.
-Don

Toto Photo wrote:
Appreciate the info, don't want to hijack the thread, but just to show how lost I am, I find it difficult to know what is changing, is it a single luminance value because it sure seems like values up and down the chain are changing.

Toto, don't worry about that! ALL questions and responses are welcome. I am just as uneducated about curves as you, probably more. All questions and explanations are welcome!

TMA Photo and Retouch wrote:
OP, once you get past the curves "scare factor"...and the curves "yawn factor"..they can be absolutely amazing tools in your kit!  Stick with it.

Will do! This thread has given me lots of new ideas, and reminded me of a few others. Great responses! All ideas and responses are welcome, even if they are "out of the box". Creative solutions have no limits!