Do you do color corrections using Curves?


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David

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#1
Just wondering... how many of you correct your images using curves? As in tweaking the individual Red, Green and Blue channels.

I find this technique to be the most accurate but also extremely tough to master/control. Have read some books out there but usually they don't dwell much on it, or they are too cheem.

Some may recommend using the Eyedropper tool -- identify which is the black, white and grey points and simply click. I find this is often one of the worst, random methods to use. What do you think? It probably works for straightforward color corrections, I feel.

So far, I find for some "tough" images which have color cast "here and there" all over the place, using curves is probably the best solution. Adjusting the Temperature/Tint controls in Adobe Camera RAW or using other tools in Photoshop does not help solve the solution completely.

I've known a few pros who do not even tweak colors using Curves, but use other methods such as the Color balance tool. Probably it's too tedious and tough to use?

How do you start adjusting? I find even after I have identified the problem color cast, and putting a point and dragging on the appropriate curves, it will affect other tonalities. It's really scary. It throws off the other colors even more and creates more problems.

Any seasoned Curves users out there who could kindly advise me on where to get good (and easy to digest!) info on color adjustments using curves? Any Curves tips are also greatly appreciated!

Thanks a lot for the help....
 

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night86mare

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#2
i think trial and error will help.

color balance is a lot simpler. no one needs that much accuracy when it comes to colors, to be honest.
 

V

vince123123

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#3
Perhaps post an example of a colour correction that is so complex that the eyedropper tool doesn't work. I personally find that it works quite well.

Of course, the version that I use is not in Photoshop, but in Capture NX, where you can drag a box to sample better than just a single point.

Just wondering... how many of you correct your images using curves? As in tweaking the individual Red, Green and Blue channels.

I find this technique to be the most accurate but also extremely tough to master/control. Have read some books out there but usually they don't dwell much on it, or they are too cheem.

Some may recommend using the Eyedropper tool -- identify which is the black, white and grey points and simply click. I find this is often one of the worst, random methods to use. What do you think? It probably works for straightforward color corrections, I feel.

So far, I find for some "tough" images which have color cast "here and there" all over the place, using curves is probably the best solution. Adjusting the Temperature/Tint controls in Adobe Camera RAW or using other tools in Photoshop does not help solve the solution completely.

I've known a few pros who do not even tweak colors using Curves, but use other methods such as the Color balance tool. Probably it's too tedious and tough to use?

How do you start adjusting? I find even after I have identified the problem color cast, and putting a point and dragging on the appropriate curves, it will affect other tonalities. It's really scary. It throws off the other colors even more and creates more problems.

Any seasoned Curves users out there who could kindly advise me on where to get good (and easy to digest!) info on color adjustments using curves? Any Curves tips are also greatly appreciated!

Thanks a lot for the help....
 

night86mare

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#4
Perhaps post an example of a colour correction that is so complex that the eyedropper tool doesn't work. I personally find that it works quite well.

Of course, the version that I use is not in Photoshop, but in Capture NX, where you can drag a box to sample better than just a single point.
one example that i can think of (but i have no such photo)

is mixed lighting, e.g. daylight with fluorescent, or daylight mixed with fluorescent and tungsten.

that would be a horror, would it not? but that involves more of layering if you must have a neutral cast on everything, and some luck to allow for layering to work fine.
 

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vince123123

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#5
Then won't it be more a case of layering rather than correction using curves?

one example that i can think of (but i have no such photo)

is mixed lighting, e.g. daylight with fluorescent, or daylight mixed with fluorescent and tungsten.

that would be a horror, would it not? but that involves more of layering if you must have a neutral cast on everything, and some luck to allow for layering to work fine.
 

V

vince123123

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#7
In your case, eyedropper will still be used, just that it is used multiple times on the same image, with masking done. Hence, still eyedropper, and not curves.

...did i not make that point already? :dunno:
 

night86mare

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#8
In your case, eyedropper will still be used, just that it is used multiple times on the same image, with masking done. Hence, still eyedropper, and not curves.
...and what did you think i meant? that we should advocate the use of a tool that i mentioned i do not advocate in my first response in this thread? just for clarification - i did not.

but thanks for paraphrasing my subsequent response to your first post over and over again, at any rate. love it when people do that. :thumbsup::thumbsup: just in case some people might not get what i'm saying, repeating it over and over again might help them. :bsmilie:
 

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David Kwok

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#9
Just wondering... how many of you correct your images using curves? As in tweaking the individual Red, Green and Blue channels.

I find this technique to be the most accurate but also extremely tough to master/control. Have read some books out there but usually they don't dwell much on it, or they are too cheem.

Some may recommend using the Eyedropper tool -- identify which is the black, white and grey points and simply click. I find this is often one of the worst, random methods to use. What do you think? It probably works for straightforward color corrections, I feel.

So far, I find for some "tough" images which have color cast "here and there" all over the place, using curves is probably the best solution. Adjusting the Temperature/Tint controls in Adobe Camera RAW or using other tools in Photoshop does not help solve the solution completely.

I've known a few pros who do not even tweak colors using Curves, but use other methods such as the Color balance tool. Probably it's too tedious and tough to use?

How do you start adjusting? I find even after I have identified the problem color cast, and putting a point and dragging on the appropriate curves, it will affect other tonalities. It's really scary. It throws off the other colors even more and creates more problems.

Any seasoned Curves users out there who could kindly advise me on where to get good (and easy to digest!) info on color adjustments using curves? Any Curves tips are also greatly appreciated!

Thanks a lot for the help....
I do, but seldom. More accurate, not exactly the word, but more flexible because you get to control high/mid/low tone at together in the same channel. Only use it when I feel the more direct tools seems less intuitive. I use it at times just to see what is possible, see if it can achieve what I want. If it does, good, if not just look for alternative.
 

#10
It's quite hard to get a good colour balance by adjusting the RGB channels individually. A better method is to use the eyedropper tool and set the white, black and grey points. For even more control, you can double click on the white, black and grey point buttons and manually set the desired RGB value. In my experience, this is the most accurate method of getting the right colour balance.

The problem I find with shooting JPEG is that if the colour temperatures are too extreme, eg very yellow lighting, etc, then there is a limit to how much you can adjust the colour balance, even using the method I have described. A better method is to either get the colour balance corrected at the point of shooting (i.e. use your camera's white balance presets or do a custom white balance). Alternatively, you can try shooting in RAW if your camera allows, as white balancing is a lot easier that way.

In response to night86mare, I think that accurate colour balance does matter to some people, especially if you are doing portraits or event photography as skin tones are important in these instances. And if that is what you are shooting, then you also need to think about the entire colour management workflow including your monitor calibration and colour management done by your photo lab. However, for casual shooting, I guess it's not that important, and you may not need to go to such an extent. It all boils down to what you need.
 

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#11
Like all tools, its not difficult once you get a hang of it.
I personally feel that using curves for adjusting colors are good for less subtle changes. I preferred over color balance and can be great for simple tweaks with only 1 curve. However, of course depends on case by case image. Curves are really not for doing major colors changes.

HOWEVER, I do not use it for that much. Reason being for file management.

There is a possibility my file could be passed to the next retoucher to work on when I'm not around. Its a lot friendly if he opens on the file and see that all color adjustments are done with color bal or even hue/sat. Without having to open each channels in curves to check.

BUT if that curve comes with a mask for a specific part of image edited. Then any minor color tweaks will be done on that curve.
 

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David

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Cool it off a bit guys.

Yes, mixed lighting is one good example where you really need precise corrections to the colors here and there. I've read an author explain this using solely curves. But the process is not very well-explained and sounded complex. He's an expert in colors and perhaps expects his audience to have a very high level of expertise in this area also. To him, no other method can match using curves when correcting colors.

Indeed, curves allow us to control precisely the individual colors at all tonalities. Please correct me if I'm wrong but using the Eyedropper method is kind of like a "brute force" way. There is much less precision. Moreover, there are times when you want to retain certain subtle colors instead of removing it completely.

Here's a problem I have with using curves now. Suppose I have identified there is a green cast in the highlights, I can move the curve at the highlight part to rid of the green. Problem is, the other parts of the curve moves also. I can of course place a point to keep that part of the curve stationary but by doing this, I find the resulting colors will not be right. Seems like I need to add more points elsewhere to refine the shape further which I am clueless how to. A slight wrong tweak and the colors wreak havoc.

The above is only a simple problem I am facing. The worse is when I needed to precisely control the various amounts of colors at different tonalities from shadows to midtones to highlights! And very often, it's impossible to edit one color channel without considering the other 2 as well, which simply adds to the complexity.

By the way, if you have an image where a mid-grey tone is not obvious, how do you find an appropriate color to click the grey eyedropper on?

Talking about colors, yeah, I do agree with night86mare than getting the colors accurate is not something critical, though it really should have been in some cases. Have looked through some photography books and somehow there is often this red or yellow cast. This is infamous for Caucasian photographers. On the one hand, we were taught how in digital photography, unwanted color casts should be gotten rid of, but on the other hand, some of the well-known photographers commit the mistake (??) of having the color casts in their books! Or maybe it's just the printing process that gets screwed up...

Thanks again, and I welcome all advice, tips and feedback!
 

theRBK

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#13
for TS, if you need to adjust the colours with more fine control, just add more control points where you do not need the colour to shift so as to tie down the curve, but be careful not to make very sharp curves... its best to do major corrections in RAW as the colour balance has not been "burnt in"... but if there needs to be finer local colour adjustments, then try to work with 16bit jpgs and tiffs which would allow greater latitude in colour adjustments... at the end of the day, for jpgs and tiffs, try different methods and use whatever is the most comfortable for you

in response to plato, what was mentioned in post #10 is probably more to do with natural looking colour rather than colour accuracy... as long as the colour looks like it is possible in real life, it is probably good enough... people have an idea of how certain colours should turn out, i.e. skies, trees, skin tones, etc., and as long as the colours look roughly possible, that is usually good enough rather than needing accurate colours... event and portrait probably aren't that colour sensitive... images requiring more colour sensitivity would probably be catalogue shots and product advertising...
 

chisiang

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#14
when you start using colour test chart, you will start to realise that you can correct the white and black easily with levels, but sometimes after correcting, some shades of grey will have different degree of colour cast. This is when you need to use individual curves to bring the colour cast to neutral.

It is extremely time consuming and the difference sometimes is not obvious and you can get away if it is not for crucial work (eg like corporate colours)
 

David

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#15
It's quite hard to get a good colour balance by adjusting the RGB channels individually. A better method is to use the eyedropper tool and set the white, black and grey points. For even more control, you can double click on the white, black and grey point buttons and manually set the desired RGB value. In my experience, this is the most accurate method of getting the right colour balance.

The problem I find with shooting JPEG is that if the colour temperatures are too extreme, eg very yellow lighting, etc, then there is a limit to how much you can adjust the colour balance, even using the method I have described. A better method is to either get the colour balance corrected at the point of shooting (i.e. use your camera's white balance presets or do a custom white balance). Alternatively, you can try shooting in RAW if your camera allows, as white balancing is a lot easier that way.

In response to night86mare, I think that accurate colour balance does matter to some people, especially if you are doing portraits or event photography as skin tones are important in these instances. And if that is what you are shooting, then you also need to think about the entire colour management workflow including your monitor calibration and colour management done by your photo lab. However, for casual shooting, I guess it's not that important, and you may not need to go to such an extent. It all boils down to what you need.
Thanks Plato. Yes, I did try the Eyedropper method but haven't found much success except for simpler cases. Hope I'm not doing anything wrong?

Anyway, hope you can kindly check my method:

1. Use 3x3 average or point average eyedropper. (Some photographers recommend one over the other. I find little difference as long as I click as accurately as possible.)

2. Set the approriate black, grey and white point values before clicking.

3. Find the black-most area (excluding complete blacks) then click with black eyedropper.

4. Find a white-most area (excluding specular highlights) then click with white eyedropper.

5. If still not optimal, find a midtone area then click with grey eyedropper.

If what I did above is correct, hmm,, sadly, I still couldn't get the colors right. By the way, as with my earlier posting, what do you do if you can't find an approrpriate midtone to click on? Trial and error? I find this to be tedious. I find setting the black and white points alone is insufficient.

Images taken with available lighting where you must take care of the human flesh tones, plus the surroundings, presents the greatest difficulty for me.
 

theRBK

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Indeed, curves allow us to control precisely the individual colors at all tonalities. Please correct me if I'm wrong but using the Eyedropper method is kind of like a "brute force" way. There is much less precision. Moreover, there are times when you want to retain certain subtle colors instead of removing it completely.
the eye dropper is rather blunt, admittedly, in that there is a lack of fine control in its effects other than adjusting the sampling of the dropper (1x1, 3x3, etc.), but in RAW processing mode, it is very convenient in setting white balance if there is a suitable point to pick off, rather than adjusting the balance sliders... and in RAW, the adjustments by the eye dropper tool to the colour would not cause massive damage to the colours as they have not been "burnt in" yet...
Here's a problem I have with using curves now. Suppose I have identified there is a green cast in the highlights, I can move the curve at the highlight part to rid of the green. Problem is, the other parts of the curve moves also. I can of course place a point to keep that part of the curve stationary but by doing this, I find the resulting colors will not be right. Seems like I need to add more points elsewhere to refine the shape further which I am clueless how to. A slight wrong tweak and the colors wreak havoc.

The above is only a simple problem I am facing. The worse is when I needed to precisely control the various amounts of colors at different tonalities from shadows to midtones to highlights! And very often, it's impossible to edit one color channel without considering the other 2 as well, which simply adds to the complexity.
this you have to practise... hold the curves stationary with control points where you don't want adjustments made, and when adjusting colours, don't just target the obvious curve, i.e. to target green, adjust green... you have to take into account the adjacent colours, say for green that would be cyan and yellow... often its the adjacent colours that could have great effect on the final colour... and in the image, target the colour to be adjusted and press the left mouse button to see where exactly on a particular curve the tone is on that curve (you will see an outlined circle on the curve) and if you want to add a point at that location just control left click it...
By the way, if you have an image where a mid-grey tone is not obvious, how do you find an appropriate color to click the grey eyedropper on?
you don't... don't have how to select... ;p
On the one hand, we were taught how in digital photography, unwanted color casts should be gotten rid of, but on the other hand, some of the well-known photographers commit the mistake (??) of having the color casts in their books! Or maybe it's just the printing process that gets screwed up...
white balance is subjective... some people like warm images, some cool... on the other hand, printers can be quite !%@% as well ;p... most important is that the image looks good to you :)
 

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sjackal

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#18
With Photoshop, there are often many ways to do one thing.

I don't know about others. I find one way that works or feel easy for me and keep doing it until I understand it.

Personally I use Color Balance instead of curves. I find it easier to understand.
 

theRBK

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#19
3. Find the black-most area (excluding complete blacks) then click with black eyedropper.

4. Find a white-most area (excluding specular highlights) then click with white eyedropper.

5. If still not optimal, find a midtone area then click with grey eyedropper.
I would suggest if colour correction is your goal, don't use the black and white droppers... its usually quite hard to see subtle colour shifts in very dark and very light areas... mid greys are usually easier to judge colour neutrality...
 

David

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#20
Thanks every one for your input one way or another.

this you have to practise... hold the curves stationary with control points where you don't want adjustments made, and when adjusting colours, don't just target the obvious curve, i.e. to target green, adjust green... you have to take into account the adjacent colours, say for green that would be cyan and yellow... often its the adjacent colours that could have great effect on the final colour... and in the image, target the colour to be adjusted and press the left mouse button to see where exactly on a particular curve the tone is on that curve (you will see an outlined circle on the curve) and if you want to add a point at that location just control left click it... you don't... don't have how to select... ;p
Thanks RBK. This is the scary part for me I guess. It's about knowing which curves to tweak. There is a tendency to correct for the particular I know is giving problems. Even if I try to target cyan and yellow for a greenish cast, they may have to be adjusted to different amounts. And like I said, sometimes, one wrong move and it's topsy turvy for the colors.

So I find adjusting by curves is really advanced and not to mention time-consuming.

And I've not even reached the part on converting it to LAB or CMYK. Haven't appreciated this part.

Sigh.. it's not easy being a digital photographer as far as colors are concerned. In the past with films, we just dumped the roll to a good print lab and accept the best results. These days, it can take me hours just to adjust a difficult image using curves.

Yes, I don't like the eyedropper tools. It's quite controversial. Some gurus say don't use it, others used simple color problems (I suspect) and showed they are effective tools. I find they never gave me consistent results. Sometimes even after I click on blacks and whites, I get weird colors. I never know what the software is doing.
 

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