Episode 094: Wine and Curves

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It’s curves time again. This powerful tool is in the centre of the stage and I try to explain it’s nearly unlimited power over colours, contrasts and brightness. Worth to learn.

This week I visit a vineyard in Missouri (too bad – only via HTTP) and discuss the dangers of blowing out the highlights under overcast sky. Just underexpose a bit when in doubt, you can get detail out of dark areas but 255 white has nothing to save in it.

The overexposed sky has killed all the details in a tree that looked over the horizon. I use the curves tool on a layer copy to get the details back and integrate the fixed tree with a layer mask into the original shot.

Then I adjust the black and white points and give a little more contrast to the image – of course with the curves tool. Finally I have some fun with – of course – the curves tool and come to an image that is not suitable for a vineyard but for a LSD factory. But they don’t have websites….


(Kevin, I made one! 🙂 )

00:20 Wine, Missouri and the Church
02:50 One image – two views
04:30 The histogram
06:40 Diagnosing overexposure
09:25 Histogram details
09:40 Linear and logarithmic
13:50 Blown out tree branches
14:30 Curves tool sight seeing
15:10 The translation line/curve
15:40 Black point
17:50 Set contrast in the curve
18:40 Bend the curve
20:30 Inspector – eye dropper
22:30 Repairing the tree
25:30 Get the blue cast out of the twigs
25:40 Adding a layer mask
29:30 Copy visible in new layer
33:00 “HDR” in a very cheap way
34:30 Power of the curve

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20 thoughts on “Episode 094: Wine and Curves

  1. Thanks for putting this episode together! I really enjoyed it and learned alot! The curves will soon be within my reach. I was thinking about the green green grass in the areas…and in seeing that the flags are in the ground for the new vines, I’d say this photo was actually taking sometime in late March/early April…do remember getting pelted by some wintery weather while taking them, but it was pretty much spring, so perhaps the green areas had a jump start with the water running through with the little creek, which dumps into the green valley floor as well.

  2. A few days ago I was looking at the histograms of various images and trying to understand what they meant. After a bit of a struggle and not much success I thought that I must put this subject as a possible video to Rolf. Perhaps there is such a thing as ESP, I don’t know but, thanks to Rolf, my understanding of the topic has improved logarithmically.

  3. Great show, Rolf. I think you already had explained some basic stuff on the curves tool, but the it is worth it a second go.

    Just one thought. As I was following along the show, I was thinking ‘now one could select the sky area to use it in a layer mask to do something with the sky’.

    Given the fact there are many branches in the sky area, it would be difficult to select it.
    But, what if you could grab an area in the histogram view and there was a tool ‘select from histogram’? Wouldn’t it be nice? Maybe this is a bit how the color selection tool works…

    What do you think, guys?

  4. Hi Bert

    Thanks for the hint. I had already visited the tutorial, but payed not all the attention it deserves as it is intended for CS3.

    I have given a fast go to it, but there is something I don’t get it; namely the ‘curves adjustment layer’. I can’t figure just now how to translate it in Gimp terms…

    I’ve tried to create a layer mask from a grayscale copy of the layer… but I think that this is something different. In the end, I could use the threshold tool for the grayscale layer mask and make some adjustments to get all the stuff black except for the sky…

    I think it is an useful tutorial, though, and I’ll spend some time to find a way to emulate the ‘curves adj. layer’ in Gimp.

    Thanks again


  5. I’ve just read the tutorial again. I think your approach is even better, jaims! You get a real layer mask or a real selection (if the color selection tool is applied additionally). With the selected or masked parts you can do everything you want. Mr. Cramer’s approachs does provide neither a layer mask nor a selection. At last it is just a way to restrict value adustments to a certain tonal range.
    It would be great to know a way to emulate adjustment layers. My attempts to transfer Photoshop tutorials to Gimp very often fail just because Gimp doesn’t know this type of layers (yet).

    Best regards,

  6. Hi again

    Meanwhile, I’ve been looking for info on the subject.
    Seems that adj. layers is something Gimp lacks (so to speak) and some photoshop users complain about.
    It also seems that Gimp could have them somewhere in the future (as GEGL improves, it would be easier to implement).

    For this particular problem, I think that the problem can be solved using a greyscale layer mask and then threshold -the way Rolf has taught us :-)-

    The set of tools the Gimp provides are enough to me. I use it for photography PP, and I don’t feel there is anything else I need (I wouldn’t mind for a wish-list open, though, I think I could put a couple of minor things on it). But watching the show, it occurred to me that it could be useful the ability of selecting ‘region colors’ from the histogram tool.


  7. You can do that.

    Make a layer copy and use the threshold tool. It has two sliders. Place the interesting part of the histogram between them. And you have your layer mask.

    I’ll look into the tutorial and try to translate it.

  8. Yeah Rolf, that is what i did, and it works fine 🙂

    I can’t recall in which chapter you taught is how to do it. In fact, I’ve used layer masks quite often, and the grayscale copy of the image is quite useful.

    A different thing is that with adjustment layers, seems that the filter you apply remains as a layer, and you can always come back to it and tune it -if you are not happy with the result. With layer masks, this is not possible (but I’m sure you can walkaround this).

    I have a copy of the photoshop elements in my laptop’s Vista partition (it was installed when I bought it, but I haven’t used it). I’ll try to get the hang of it in order to see if I’m able to find a way to emulate this behavior with the Gimp.


  9. Well, I think that maybe I misunderstood last post; you say I can do ‘select from the histogram’ with this workaround?
    I was sure I could workaround this; but still, it would be nice to have a tool that allowed to go directly from a zone in the histogram to a selection. I don’t know if I am being able to explain the idea?


  10. I assume it is quite easy to write a script that’s doing the desired histogram-to-selection-job (although I can’t count anymore how often I was deceived by my initial estimation ;-).
    I’ll try it in Python as soon as there is a little time for it.

  11. I read the Lumininous Landscapes tutorial. He is doing basically the same as I did with the blown out tree. I got the tip to use more points to fix the curve.

  12. @Jaims: Adjustment layers are exactly what you think they are. They (better: nondestructive editing) will come to GIMP in a better way, but I have no idea when and how.

    There are ways around for a lot of operations – but I have no idea how to make that with a curve.

  13. Hola jaims,

    I tried to write the mentioned script. Then I realized that executing the task by using the script would require even more clicks than doing it by the described workaround. The easiest way to get the selection is just to apply the color selection tool to the mask provided by the threshold tool (it was again an initial false assessment on my part; this script really doesn’t make any sense).

    Best regards,

  14. Hola again

    Yeah, @Bert; it would be a tool that would do the same selection than the color selection tool; that much is clear to me. It would be another way of seeking the same result, which quite often is a good thing to do.

    For instance, there you can retouch colors via several tools, namely I would use either the curves tool or the level tool. They are not equivalent but similar in many senses, and I tend to always use the former.

    Likewise I was thinking that I’d be probably feeling more comfortable with a tool like ‘select color from histogram’ than with the color selection tool. See what I mean?

    All the same, thanks for your effort and work with the hypotetical ‘color from histogram’ selection script :-). Makes it sense or not because so many clicks needed, as you put it, is the least important thing here, I think; the important one is the great ability that Gimp provides us with, in regards of extending functionality.

    @Rolf, thanks for your two cents on that. I read that adjustment layers (I think that they must be great, but haven’t got to know them yet) will be maybe implemented as of Gimp 3.0; being the integration of GEGL a previous milestone which will provide the basis to easily implement them.

    Nice thread, thank you all


  15. I’m catching up, already at episode 94 …
    In fixing the trees, we saw a false color (in this case, blue). When working on segments in the curve, distorting them, I also get other false colors, e.g. yellow, pink … Where do those false colors come from while working simply on all 3 channels combined ? and: how to get rid of them ? (desaturate ist too simple a solution for most occurrencies !). <<

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