Curves

[Ysarex]

So my first post was badly expressed. I was being indirect and did a bad job of it.

I'll try again: If you want the best possible photo and your goal is a straight photo (no special effects). Shoot a RAW capture and get it right in the RAW to RGB conversion process. If you do that you'll have the best result and, you won't be grabbing Curves in Photoshop to continue editing the RGB photo.

Joe

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[unpopular]

curved can do everything levels can, but levels cannot do everything curves can.

[unpopular]

So my first post was badly expressed. I was being indirect and did a bad job of it.

I'll try again: If you want the best possible photo and your goal is a straight photo (no special effects). Shoot a RAW capture and get it right in the RAW to RGB conversion process. If you do that you'll have the best result and, you won't be grabbing Curves in Photoshop to continue editing the RGB photo.

Joe

I prefer to think of the RAW file as the unprocessed film, the TIF file as the negative and the working file as the print. When I am creating a RAW file, I want to get a good capture with as little noise as possible and as much detail as it can hold. In the RAW processor I am looking to compress that data into a gamma curve which will contain all the information I need and the working file renders that information in a way which makes visual sense.

[KenC]

{snip}....and also there can be a lot of selective curves adjustment applied only to parts of the image, which really is not possible in raw conversion.

Basically yes if you live in an Adobe centric world and most of us do (I do use ACR). However what you're describing as local tone adjustments is possible if you use a different converter. Capture 1 is very capable of processing a RAW file via multiple layers and tone and color adjustments applied locally.

Joe

Hmmm... Capture 1 you say? Thanks for the tip - I'll have to look into that. I wondered if there was a converter that allowed this (neither DPP nor ACR does). I've never had any banding or other trouble from doing my selective curves or other adjustments in PS, but even so it would be better to do more in the conversion process.

[KenC]

I agree that one should do most of the global curves adjustments in the raw conversion and that large global adjustments after that point might argue for going back and re-doing the conversion. However, there are always global curves tweaks that need to be done after other adjustments, and also there can be a lot of selective curves adjustment applied only to parts of the image, which really is not possible in raw conversion.

If I remember right the curves panel in Lightroom may be a little more limited than the one in photoshop?
Also what about Curves in LR vs ACR?

No idea about LR - never used it, only Canon DPP and ACR.

[gerardo2068]

I think in LR you only get dark and light only tonal curve, for like contrast. I think

[Ysarex]

{snip}....and also there can be a lot of selective curves adjustment applied only to parts of the image, which really is not possible in raw conversion.

Basically yes if you live in an Adobe centric world and most of us do (I do use ACR). However what you're describing as local tone adjustments is possible if you use a different converter. Capture 1 is very capable of processing a RAW file via multiple layers and tone and color adjustments applied locally.

Joe

Hmmm... Capture 1 you say? Thanks for the tip - I'll have to look into that. I wondered if there was a converter that allowed this (neither DPP nor ACR does). I've never had any banding or other trouble from doing my selective curves or other adjustments in PS, but even so it would be better to do more in the conversion process.

Ken,

Phase 1 has a 30 day free trial. Capture 1 is pricey but if it's your bread and butter nothing's better. It's not nearly as sophisticated as Photoshop's layers but you can basically mask off a section of your photo and then apply local changes to both tone and color. And you can stack multiple masked areas. I don't know any other RAW converter with this ability. There's also a fabulous local color editor that's much better than what ACR provides. My one big gripe about C1 is CA correction. They only provide CA correction for lenses in their database and it's an auto only correction -- no manual hand tweaks. If your lens is supported it's good enough but DPP and ACR are better (OEM often is).

Anyway, C1 is good enough that I can usually get the photo done there except for pixel level edits. C1 will also straighten a photo and make adjustments for convergence which is pretty cool. You should take a look.

Joe

P.S. I agree that applying tone/color adjustments in Photoshop especially on 16 bit RGB files is going to be worth doing if needed and I'll certainly do it, but as you say above, "but even so it would be better to do more in the conversion process." That is my original point -- I think you and I completely agree.

[Ysarex]

curved can do everything levels can, but levels cannot do everything curves can.

Not exactly, at least not in Photoshop. The midpoint slider in Photoshop's Levels works differently than pulling the midpoint of the curve. The difference is subtle but it can matter.

Joe

[Buckster]

curved can do everything levels can, but levels cannot do everything curves can.

Not exactly, at least not in Photoshop. The midpoint slider in Photoshop's Levels works differently than pulling the midpoint of the curve. The difference is subtle but it can matter.

Joe

Interesting.

First, show us how it can matter. Second, show us that the result made from levels can't be achieved with curves.

[Buckster]

In your post you mentioned the RGB channels so I'm going to assume you're referring to the use of Curves and Levels as applied to RGB photos.

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.

Here's what else you should know:...{snip}

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.

[unpopular]

curved can do everything levels can, but levels cannot do everything curves can.

Not exactly, at least not in Photoshop. The midpoint slider in Photoshop's Levels works differently than pulling the midpoint of the curve. The difference is subtle but it can matter.

No. Gamma is gamma. Multiply the gamma coefficient(?) by 127 and enter this into the output of level 127 (or whatever scale you are using) in curves. The results will be the same. What levels does do is visually represents the midpoint in a meaningful, though a bit esoteric, way.

[Ysarex]

curved can do everything levels can, but levels cannot do everything curves can.

Not exactly, at least not in Photoshop. The midpoint slider in Photoshop's Levels works differently than pulling the midpoint of the curve. The difference is subtle but it can matter.

Joe

Interesting.

First, show us how it can matter. Second, show us that the result made from levels can't be achieved with curves.

Happy to.

First lets make sure we know the question: Unpopular (whom I hold in high regard) posted a graphic above implying that the endpoint sliders and midpoint slider in Levels were effectively equivalent to the end nodes and a midpoint node on the Curves line. Close enough for government work.

I noted that in fact pulling the midpoint slider in Levels isn't going to give you quite the same result as pulling a node placed on the center of the Curves line and that the difference can matter. I noted this is Photoshop exclusive as other software may implement other algorithms.

The difference is this: Place a node on the center of the Curves line and pull it up or down and the photo will lighten or darken. Likewise pull the midpoint slider in Levels to the left and the photo will lighten, pull it to the right and the photo will darken. Make a change with the midpoint slider in Levels and any attempt to make a change of the same degree using a node on the center of the Curves line will produce a higher contrast result: that matters. It can matter a lot.

Here's a visual example. I started with this image:




I made a Levels change and pulled the midpoint slider to a value of 1.45. Note the inset histogram:



I went back to the original, brought up Curves and placed a node on the center of the line. I picked a reference point in the photo and matched it between the Levels and Curves versions. It doesn't matter how you try and test this. There is no position to which you can move that node in Curves that will produce as low a contrast image as you were left with making the Levels change. Note the inset histogram and compare it with the one above.



In Photoshop, the midpoint slider in Levels will lighten or darken your photo and give you a lower contrast end result than anything you can get using a center line node in Curves; and it matters because it can really influence what you'll ultimately get as you continue on.

Joe

[unpopular]

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.

[Ysarex]

curved can do everything levels can, but levels cannot do everything curves can.

Not exactly, at least not in Photoshop. The midpoint slider in Photoshop's Levels works differently than pulling the midpoint of the curve. The difference is subtle but it can matter.

No. Gamma is gamma. Multiply the gamma coefficient(?) by 127 and enter this into the output of level 127 (or whatever scale you are using) in curves. The results will be the same. What levels does do is visually represents the midpoint in a meaningful, though a bit esoteric, way.

This could end up being one of those cases where we're talking about the same elephant form different perspectives and in fact we agree its an elephant. I didn't say Curves can't replicate the same result you get from Levels. I said you don't have a midpoint to midpoint equivalence. For example in the photo I just posted you can't place a node anywhere near the midpoint of the Curves line and get a result equivalent to pulling the midpoint of the Levels slider.

So I was reacting to the original graphic that drew an equivalence between the Levels midpoint slider and a node mid-line in Curves.

Joe

[unpopular]

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.