using curves

[Ysarex]

This is actually a point where GIMP wins. You can, albeit with a little effort, perform operations like curves in HSV-land, and peel out the resulting values (or whatever). Effectively.

This is basically a problem with every tool, though. I guess you can argue that curves is nastier than other tools, but they all do a bunch of stuff to a picture, while essentially advertising one of the effects as 'the thing they do'. It's kind of an inevitable consequence of the way the universe works.

Jay's post didn't go in to any of this, though. It was just some ranting, backed up with some vague remarks about light and some incorrect remarks about Ansel Adams.

I'm not advocating Jay Arraich's position. I just grabbed that from wayback because he caused such a stir with it about 10 years ago -- it's a great title and I just wanted to start stirring things a little.

Yes, GIMP will allow you to decompose an RGB photo to HSV and then apply a curves adjustment to the Value channel. Photoshop likewise will perform a Curves adjust to a photo in Lab mode. And in fact you can download a plugin from Adobe that will let you convert an RGB photo to HSV/HSL. It's a legacy plugin from CS4 but it still works with CS6. Here's the link: Adobe - Photoshop : For Windows : Adobe Photoshop Legacy Optional Plug-Ins and ReadMe

Yes, all digital editing tools are double edged and I would argue that Curves has above average potential to sneak up and bite you from behind when you're not looking.

Joe

 

[mmaria]

I thought that OP asked for some basic understanding of curves, and I think he is pretty much overwhelmed now but again, maybe I'm wrong.

English is my second language and I'm not good when it comes to explaining something complex as curves are. I didn't even know that word "abomination" had to google it and had to completely disagree, but this thread isn't about that.

When I started to use Gimp I was overwhelmed. I had to learn much to get somewhere, because there are so many tools that needed to be understood. Switching to Photoshop was also a challenge.
Learning about mentioned gimp/ps lead me to curves and I admit I was using them just for contrast and white point for a while. The curves were maybe just on one layer when editing a photo. Some time and some more learning led me to drop some other tools out of use and include curves much more. They are now simply a must tool for me.

As mentioned, OP has to understand how much harm will a tool do when it's been used to alter something in photo. I'll mention dodge and burn, because those tools are pretty much among the first ones, one learns in ps.

I know I settled with curves. I like how they give me much more control in editing than any other tool in ps, I'll even do some retouching on people faces with curves. But it's been quite a learning journey to get here.

Ysarex mentioned increasing contrast will bump saturation, so how to fix that if you don't want more saturation? One has to know blending modes.
How to apply curves on just a small part of the photo? One has to know about layer masks. etc. etc.

My point is that one has to know about many stuff in order to get the best out the curves. I'll just type what it comes to my mind this moment: layers, layer masks, layer's/mask's opacity, blending modes, adjustments vs. adjustment layers, opposite colors, tones, brightness, sharpening, levels vs. curves, channels, what does it mean input/output or the hand in curves panel...

For someone who is just introduced wit editing photos curves can be overwhelming, but certainly not an abomination

 

[j_c]

I actually took photography in college (10 years ago yikes!) so i have understanding of editing but obviously things have changed quite a bit since then and it's been awhile since I have used them.

 

[Ysarex]

I actually took photography in college (10 years ago yikes!) so i have understanding of editing but obviously things have changed quite a bit since then and it's been awhile since I have used them.

I actually took photography in college too, but that was over 30 years ago and things have really changed since then.

Sorry about the Jay Arraich abomination article stirring things up -- I couldn't resist. I would need to know more specifically what you're doing to be more helpful, but in all seriousness I would recommend staying away from Curves in Photoshop. You shouldn't need it and if you're using it I would question what you did to get to that point in the first place and recommend you turn your attention back there. I rarely ever use Curves in Photoshop and never to make tonal adjustments.

Joe

 

[amolitor]

Where DO you use curves? Is it part of your raw processing?

I'm not convinced that it is possible to go from raw to print without applying a curve someplace.

 

[Derrel]

Where DO you use curves? Is it part of your raw processing?

I'm not convinced that it is possible to go from raw to print without applying a curve someplace.

The image that comes off of a sensor and has been demosaiced usually looks like an almost-black box, with pretty much everything a dark,dark,dark gray mess. Until a tone curve has been assigned, it's often difficult to even tell who or what is contained within the borders of the image. It looks a lot like this, until a tone curve has been applied.

 

[amolitor]

Yeah, at some point a curve is gonna get banged on there, and Joe doesn't seem the type to let some default get applied and call it good!

 

[Ysarex]

Where DO you use curves? Is it part of your raw processing?

I'm not convinced that it is possible to go from raw to print without applying a curve someplace.

Every raw converter applies a curve to the raw data but they don't all provide a typical curves control that will allow you to place multiple nodes on a line and start pushing and pulling. I do most of my raw conversions in Capture one and PhotoNinja. C1 does have a conventional curves adjustment, but PhotoNinja does not. That doesn't mean PhotoNinja isn't manipulating the tone response or applying a "curve" -- that has to be done, but PhotoNinja's tool set to accomplish that doesn't include the classic curves adjustment box.

Using a classic curves control box in a raw converter is fine; again it should be used very carefully and I would still argue there's probably better alternatives, but if you are going to use curves, that would be the place to do it. By the time the photo has been converted to RGB and moved into Photoshop you should be past the point of still needing Curves (thus my suggestion).

So I processed some photos this morning and I ran them through PhotoNinja and then Photoshop. I never saw a classic curves adjustment dialog in that process. Yes, PhotoNinja allowed me to adjust the tone response of the photo which I did and in a generic sense it applied a tone curve to my raw data. In Photoshop I did a little fine-tuning darkening the corners which I could have done using a Curves adjustment layer and mask, but that would have been unnecessarily complicated.

Joe

 

[mmaria]

Ysarex, I'm just curious now, what tools do you use in ps?

Sent from my LG-P700 using Tapatalk

 

[Ysarex]

Ysarex, I'm just curious now, what tools do you use in ps?

Sent from my LG-P700 using Tapatalk

I work from raw files which is a critical point. If I were trying to repair a camera JPEG then I'd make heavier use of Photoshop and could conceivably use Curves in that circumstance, but still unlikely. As it is I don't do a lot in Photoshop because by the time I get to Photoshop there's not much left to do. Here's one of the photos I processed this morning.

Starting with the sensor capture:



That's for Derrel and Amolitor. The Bayer array is still in place so it has a green tint and yes it could sure benefit from some processing including application of a tone curve.

This then is PhotoNinja's default rendering of the photo:



PhotoNinja has applied a basic tone curve and picked up the white balance setting from the camera. I leave the camera set to auto white balance normally when I take photos outdoors so that's botched.

So I went to work in PhotoNinja: I corrected the WB and adjusted that tone response. I made the blacks blacker, raised the contrast and brightened the photo a tad. I take a conservative position when converting the raw file to RGB and typically leave the contrast a little low and I leave some room at the highlight end. Here's the RGB conversion:



In Photoshop then I cropped the photo and tweaked the overall tone response. I raised the contrast a little more using a Soft Light blend and a dupe layer which I desaturated so that I would only raise contrast. I had to tweak the highlight slider in Levels to a value of 249 to place the highlights. Then I switched the photo to Lab mode and working on the Lightness channel I burned down the corners and background by painting the Multiply blending mode with the History Brush at a low opacity. Here it is finished:



Joe

 

[mmaria]

Ysarex, the way you wrote all this (confidently) "skip using curves" intrigued me a lot... but you didn't explain exactly why are they soo bad? With all things said in this thread but without exact explanation how and how much will curves harm a photo ( mentioned subtleties) I would call your editing as your personal preference.

I do understand your workflow, agree with you to some point and some things you do, I do exactly the same, so nothing to explain there.

I shoot raw and do everything I can in CR before I go to PS. I've never used PhotoNinja.

Whole editing process, software are really an interesting subject for me. There are million things you can do in PS and I want to know them all (yeah right!?) So, me asking all this means that I want to learn and understand more and not advocating or defending my opinion.

 

[Ysarex]

Ysarex, the way you wrote all this (confidently) "skip using curves" intrigued me a lot... but you didn't explain exactly why are they soo bad? With all things said in this thread but without exact explanation how and how much will curves harm a photo ( mentioned subtleties) I would call your editing as your personal preference.

I do understand your workflow, agree with you to some point and some things you do, I do exactly the same, so nothing to explain there.

I shoot raw and do everything I can in CR before I go to PS. I've never used PhotoNinja.

Whole editing process, software are really an interesting subject for me. There are million things you can do in PS and I want to know them all (yeah right!?) So, me asking all this means that I want to learn and understand more and not advocating or defending my opinion.

First it's really important to draw the distinction between Curves in Photoshop as applied to an RGB image and curves for example in LR/ACR or some other raw converter. I'm specifically referring here to Curves in Photoshop and my remarks do not necessarily apply to a curves implementation in other software.

My response in this thread isn't because Curves really is soo bad it's that there is usually a better way to achieve the end result and Curves is so abused and misunderstood. You should also consider that my reaction is colored by my regular experiences with my students. I'm teaching a class right now in advanced Photoshop and unfortunately I sometimes feel like my primary job is to correct all the horrible practices they've already learned. I blame Youtube as well as regrettably some of my colleagues.

So you want some specifics: Let's start with those bleep bleepin' eyedroppers in Curves. I'm in class watching one of my students. He takes the white eyedropper and begins searching around the photo clicking on white spots. I wince. Next comes the black eyedropper and a similar click-here-and-there exploration to find a black point. I wince. "What value did you set for the white dropper?", I ask. "Huh?" he says. "If you don't set a maximum highlight value for the white dropper Photoshop will leave it at 255. Do you want to set your whites to 255?", I ask. "Huh?", he says. "How did you determine that the point in the photo you selected for white really should be neutral?", I ask. "Huh?", he says. "Where did you learn to do this?", I ask. "In my digital photo class last semester," he says. I drop my head and start shaking it.

So can you come up with a legitimate use for those eyedroppers when working on an RGB photo? Assuming you know more than my students you would start by setting values for the white and black droppers; say 246 for white and 4 for black. Now how do you determine the white point you're going to use in the photo? Is there a white point? You could use the highlight slider at the bottom of the Curves box and hold the option/alt key to find the brightest point in the photo. Say you select that point. Have you made sure it's not already above the 246 value you set? Abominations will happen if it is. Are you sure it's really neutral? If it's a value below 246, say 238, is it 238 in all three channels or should it have been? Are you tone adjusting the photo or white balancing it? That white dropper will set all three channels to 246 and redraw the curve for each channel. Sure you want to do that? And do that again with the black point? You're not just setting white and black tone values, you're also white balancing on those two points. It's a bad idea to white balance on a very bright point and a worse idea to white balance on a very dark point. Anything even worse? yep, doing them both.

Overread referenced Ron Bigelow's tutorials earlier and they're pretty good. Ron has a long tut on using the white and black droppers. The whole thing reads like one long warning and at the end you should be pretty wary of those droppers. Ron's conclusion: "The Eyedroppers are a great tool, but only for photographers that are willing to study their images to determine the color nature of the highlights and shadows and to customize the use of the Eyedroppers to the specific needs of each image. In other words, a photographer can not blindly apply the eyedroppers to all images in the same way and expect to get good results. The use of the Eyedroppers must be customized for each image."

Compare Ron's lengthy warning with this:



You really have to watch that -- it's from a bona fide guru: techguru77. There really should be some way to punish techguru77 for Curves abuse. I'm not going to live long enough now to go to Youtube 4 hours a day and add a corrective comment to all the Photoshop tutorials that show people how to trash their images.

I know the eyedroppers are in Levels as well and they do the same thing. So something more specifically Curves unique then: OK, one of the problems with using Curves to raise contrast in a photo with a typical S curve is that the S curve is curved. Which is of course the whole point. One of those duh moments when you figure it out. By placing a node on the line near the highlights and pushing that node up you change the slope of the line in the brightest highlights and compress them. As Ron notes in his tutorial on Curves this will introduce quantization errors. But it does more than that. For the sake of increased midtone contrast you're compressing highlight contrast. You want a steeper line in the mid section to raise contrast. If you just steepen the line by pulling the white point over to the left (Levels highlight slider) you'll get that steeper line but you may be clipping critical highlights. With the S curve Curves allows you to steepen the mid section of the line by placing a compression curve in the highlights and so avoid highlight clipping. If that were my only option I'd do that but do I really want to do that? Do I have other options? Which takes me back to my earlier remark there's usually a better way to achieve the end result. This is an example of Curves' double edge cutting painfully deep. I'll bet techguru77 has a tut on how to use Curves to fix contrast.

Joe

 

[mmaria]

I started this post several times and none of the words were right...

I completely understand your point of view after I heard all this students experience and can't believe I watched this techguru77 all 4 minutes of my life! And as you said there's probably much more of "those" tutorials on web... it makes me mad and sad in the same time. They there are and there is nothing one can do to stop they or their influence.

Thank you for clarifying all this and let's hope that someone will make an effort to learn more and to learn from someone legitimate (if that is a proper word to describe someone who has true knowledge)

Maybe you did some good with all you wrote here in this thread

 

[Ysarex]

I started this post several times and none of the words were right...

I completely understand your point of view after I heard all this students experience and can't believe I watched this techguru77 all 4 minutes of my life! And as you said there's probably much more of "those" tutorials on web... it makes me mad and sad in the same time. They there are and there is nothing one can do to stop they or their influence.

Thank you for clarifying all this and let's hope that someone will make an effort to learn more and to learn from someone legitimate (if that is a proper word to describe someone who has true knowledge)

Maybe you did some good with all you wrote here in this thread

Thanks. I'm afraid Youtube is overrun with techgurus. There's good content there as well, but the bad content tips the scale and the bad content is too often really really bad.

So again I'll say that if you're doing everything right to achieve maximum image quality you should not be doing much with Curves in Photoshop.

That said here's a tip for a uniquely valuable use of Curves in Photoshop. Consider this photo:



The greens in the lawn and trees may be pretty accurate but they're on the blah side (should have fixed that in the raw converter). Maybe a little saturation boost? Most people using Photoshop would head straight for the Hue/Saturation dialog and from the drop box select Greens and then raise the saturation value. Green grass and foliage is actually yellow-green so you'd have to expand the target range to include yellow. Here's the same photo with the yellow-green saturation increased to a value of 20:



In the RGB color model saturation and value are linked. It's the same issue I raised about using Curves to increase contrast and experiencing a secondary effect of increased saturation at the same time. In the Hue/Saturation adjusted version above the grass and foliage show a brightness increase as well as a saturation increase. (I could have compensated with a Lightness change). Furthermore the saturation/brightness increase is equal in both the yellows and greens and it would be much better if that increase could be weighted to more green and less yellow. Not easy to due with the Hue/Saturation control.

So here's a third version adjusted using Curves:



The difference is subtle but then we want to remember what Michelangelo told us, Trifles make perfection, and perfection is no trifle. In this version the saturation increase is weighted toward green and the brightness increase that resulted from the Hue/Saturation adjustment isn't there. I altered the photo's color mode from RGB to Lab and then applied Curves adjustments to the two color channels. I increased the green saturation and then the yellow saturation a little less. With a photo in lab mode the "a" channel is green/magenta and the "b" channel is yellow/blue. To increase green saturation I placed a lock node at 0, 0 and another at 64, 64. Then I dragged the lower left corner (green) in. The "a" channel upper right corner is magenta. Did the same in the "b" channel (yellow is the upper right corner) but to a lesser degree.



This is a good use of Curves because there's no better way to accomplish the same result (except you should have got it done in the raw converter).

Joe

 

[mmaria]

You just gave a big reason for people to dig into curves possibilities.

Curves are still my favorite tool. They push me to think about every slightly change I want to make and I find that the most interesting and challenging.

Maybe I'm used to my workflow and thinking about all you've said maybe I need to remind myself on some different ways/options to achieve certain things, just to practice a bit more with forgotten tools.

.... Maybe a little saturation boost? Most people using Photoshop would head straight for the Hue/Saturation dialog and from the drop box select Greens and then raise the saturation value...

Do people really do that?