Curves

[Ysarex]

That is significant, and I am thinking its an interpolation error, either intentional or not. The more I think about it, the more it really does make sense.

Regardless though how inaccurate curves renders gamma, the basic principle is maintained nonetheless.

Still, just for the sake of the experiment, try entering 184 into the output field of level 127 in Photoshop's curves. I will do the same in photoline under different interpolations.

It's late and here I am a couple beers down, but I think I got it. First off I reacted to the graphic and, no offense intended, but I've seen that before -- the line between the Levels midpoint and the Curves midpoint -- I knew from practice they didn't do the same thing. In fact I think they would be the same if the histogram distribution were a theoretical bell curve. That just never happens in practice.

So I've run into photographers before telling me they're the same. Well, no, not if the histogram weights to one side or the other, and it does in the photo I grabbed. This is really a discrepancy between theory and practice. You have to expect Curves could replicate the Levels result. But it's not going to work from the midpoint on the Curves line.

Joe

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[gerardo2068]

Good stuff

[Ysarex]

Well, you have to consider how both tools work, one works using a lookup table, interpolating the values between points, the other uses arithmatic. So it makes sense that they might render a bit differently. Adobe may also interpolate the curve in a way which is more accurate.

Look at these two curves that I applied to the same image of the flower from above. I worked pretty hard to make the curves the same. The visual results are dramatically different. It depends on where you pull the node from. The image in which the node is pulled from the midpoint (left curve) is much higher contrast than the other. The shape of the curve isn't all that matters. By pulling the node from near the shadow end I was able to get a contrast result that approximated the earlier Levels change that I made, although the color saturation remained different.

Joe

[Ysarex]

As opposed to...?

As opposed to the RAW capture. ACR does have a Curves tool and I do use it. Goal is to get tone response and color right in the RAW to RGB conversion. If you do the RAW to RGB conversion and then you need to use Curves to adjust the tone response, didn't you miss something?



I use Curves to adjust the tone response of my RAW files as part of the process to convert them to RGB. Once they're RGB that job should be done.

At this point, I think you're thoroughly confused, but maybe it's me. If you give a bit more explanation, I'm pretty sure that at least one of us is going to learn something in the process, so please do expound upon your thoughts here.

I'm not confused, but I'll agreee I didn't do too good a job expressing myself.

I know it's common for a lot of photographers to shoot camera RGB photos and then to edit those. So I was saying that's not the way to get the best possible result.

Joe

Sounds like 6 of one, half a dozen of the other to me. You appear to be talking about workflow processes and what you feel are best, and they don't include much beyond global adjustments in the conversion from RAW. I would say if that's what works best for you, great, but if others choose a different path than you to get to their end result, that doesn't mean they're doing it "wrong".

A lot of very skilled and knowledgeable people find curves in Photoshop very useful, and they've obviously already converted from RAW at that point. Seems awfully pretentious of you to say or even infer that they're doing it wrong.

I never said "wrong" and I don't want to sound pretentious. I know a lot of people edit either camera produced RGB photos or already converted RGB photos. I'm trying hard not to make it black and white by just saying something like "wrong." I said I want the best possible result. And my experience tells me you get that by getting as much right up front in the RAW conversion process as you can. I'll stick by that.

Joe

[unpopular]

I hear you, my tests are indicating the same results. But I am not sure you completely understand what curves are actually doing. In the first example you did not adjust the middle point. I can't see your input value, but you've translated another level, and not level 127. This is kind of an arbitrary adjustment.

Instead of moving the middle point up and down, try moving it left and right:



As you can see, the two are much closer, such that I am guessing that what any slight variation is carelessness on my part. If this is the case, what this indicates is that the gamma operation in levels is being performed on the input value and not the output value - as I initially assumed. Which makes sense, as the levels being adjusted are labeled the "input levels".

[unpopular]

Also. I have no idea why I thought simply multiplying the gamma value by the target would work...

I am working on a conversion atm.

[Ysarex]

I hear you, my tests are indicating the same results. But I am not sure you completely understand what curves are actually doing. In the first example you did not adjust the middle point. I can't see your input value, but you've translated another level, and not level 127. This is kind of an arbitrary adjustment.

Instead of moving the middle point up and down, try moving it left and right:



As you can see, the two are much closer, such that I am guessing that what any slight variation is carelessness on my part. If this is the case, what this indicates is that the gamma operation in levels is being performed on the input value and not the output value - as I initially assumed. Which makes sense, as the levels being adjusted are labeled the "input levels".

I do understand what Curves is doing. I've suffered through this before. I've tried everything I can to make the Curves result match the Levels result and that includes holding the input value at 127. I've tried starting with a node on the line at 127 and then pulling that node. I know that can change the input value if you pull the node in multiple directions. I've tried that and you get a higher contrast result from Curves. I've tried it by the numbers. Type in 127 as an input value and don't change it. There is no output value that you can enter that will produce the same result that you get from Levels -- the Curves image will always be higher contrast. I've even tried it backwards (hold the output to 127) and that really doesn't work. Again I stress that this is specifically Photoshop behavior. There may be some characteristically ideal photo in which this doesn't happen; I haven't found it.

I'm describing what actually happens in Photoshop -- not what should happen. I learned this years ago as a matter of practice. In fact I ran into first in a book where they had a similar illustration that drew the same relationship between Levels end and midpoints and the ends and middle of the Curve. I tried it and wound up scratching my head. I put it down to Adobe's implementation.

Joe

[unpopular]

That is REALLY pretty odd. I don't have a copy of photoshop right now. But heck, I'm tempted to download the demo just to try. I have no idea what to think really. Photoline seems to translate the curve similarly to the Levels. I wonder about GIMP. I'm almost inclined to say it's a flaw within Photoshop, or an attempt to make curves more user-friendly.

It's almost as if Photoshop is applying the curve non-linearly.

[Ysarex]

That is REALLY pretty odd. I don't have a copy of photoshop right now. But heck, I'm tempted to download the demo just to try. I have no idea what to think really. Photoline seems to translate the curve similarly to the Levels. I wonder about GIMP. I'm almost inclined to say it's a flaw within Photoshop, or an attempt to make curves more user-friendly.

It's almost as if Photoshop is applying the curve non-linearly.

I've been tempted more than once to pick up a copy of Photoline.

I've never assumed that Levels and Curves should behave the same way, but I'm completely happy with that. If so then Adobe is puttin' some English on the ball so to speak. Anyway I wanted you to see one where you could read the numbers yourself so you know I'm not nuts.

I started with this photo (unedited) because of the pot on the bench. I filled the pot with a solid grey value 127.




Made a dupe of the photo and then took the first one into Levels and pulled the midpoint slider to the left until the pot value was 158. Then I took the dupe into Curves and set the input to 127 and the output to 158. While I was at it I again tried to free-hand that Curves node to a position where the two photos had the same contrast and density -- not possible.

Joe

[unpopular]

Try entering the output to 127 and the input to 158 in the above example.

Photoline is cool, there are some really cool lower level features that Photoshop doesn't have. It takes some time to get used to.

[Ysarex]

Try entering the output to 127 and the input to 158 in the above example.

Photoline is cool, there are some really cool lower level features that Photoshop doesn't have. It takes some time to get used to.

Yep, tried that long ago -- that just gives you a darker and still higher contrast image.

For what it's worth it may be Photoshop's implementation of Levels that's "off." Frankly I don't care that much. I don't dig into the numbers so much as I pay attention to what I see. The key in all of this is contrast. Photoshop's midpoint slider in Levels doesn't raise contrast while the midpoint node in Curves does. I'll gladly leave it to you to come up with a numerical explanation -- I know how to manipulate them to advantage.

I hear nothing but good about Photoline and the price is insanely cheap. I hate to add new software to a stable system, but soon enough I'll probably add that one. Wow! now there's a thought. I already rely on Capture 1 as my primary RAW converter. If I went from C1 to Photoline to finished output I'd be Adobe free. Wow! Adobe free -- is it possible?!

Joe

[unpopular]

I am proud to say that I am Adobe Free, but i am not professional either. I still haven't found a good prepress workflow, and I don't know enough about the demands of a propho to really say if Photoline is good enough. I have downloaded the Capture 1 demo, I haven't tried it yet. I'm using Raw Photo Processor (mac only) right now, it's extremely precise and produces the sharpest images I have seen yet. It's REALLY clumsy to use, it's like using a film processor.

Anyway, the big thing I like about Photoline is that you can edit RGB, LAB or HSL without changing the mode of the image layer. Working directly in HSL is just AWESOME in itself. You can make saturation adjustments on a curve. So you can actually make less saturated colors even less saturated, and more saturated colors more saturated. Or you can make warm colors warmer and cool colors cooler by adjusting the Hue curve. This all doesn't sound like much, but it really adds to the vibrancy and depth of the image.

[unpopular]

I edited your photo using the techniques mentioned. As you can see contrast is implied through color, rather than tone, making for a subtle contrast adjustment without affecting shadow/hilight detail.



(not saying it's an improvement, just as an example)

[gerardo2068]

Can you give me example where I would want to you use Curves adjustment in a specific color channel? Like on the drop down menu you can choose red green or blue. I understand the RGB setting. You could use it to make it brighter or darker, add contrast and things like that. But beside a few tutorials where they use the other setting to make the photos looks pastel color, I can't think of any other situation. I'm beginner on PS.

[Ysarex]

I edited your photo using the techniques mentioned. As you can see contrast is implied through color, rather than tone, making for a subtle contrast adjustment without affecting shadow/hilight detail.



(not saying it's an improvement, just as an example)

Drifting off topic here, but what the heck.

That is a very intriguing feature! I achieve a similar result with saturation in Photoshop by accessing the Lab color channels independently, but that would be much more direct and convenient, I'm heading over to the Photoline website again to study up.

Joe