Histogram, levels and curve relationships

jacques

• December 25, 2014 08:06

Hi all,

Could someone please clarify the relationship between the histogram, the levels and the curve ? I tried understanding by playing with each of them separately, figuring out how one would impact the others; but so far I did not really get it.

On an image with no edit at all, the histogram and the levels are slightly different - why is that ? Changing the exposure impacts the histogram, levels and curve. Changing the levels impacts the histogram and the curve. Changing the curve impacts only the histogram.

This is certainly a very basic question for most of you, but I would really appreciate some clarification (or a link to some solid documentation 😊)

Thanks for your help.

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  Ian Wilson

  Moderator

  • December 25, 2014 11:11

  

  The histogram is related to the output you get, and even with no edits the histogram may look different from what you see in the levels tool because it is affected by the ICC profile that is selected in the process recipe (on the output tab). Generally my process recipe is set to sRGB Color Space Profile. In that case the histogram does look different from what I see in the levels tool. But if I change the ICC profile in the process recipe to "Embed Camera Profile" the histogram changes and looks the same as in the levels tool.
  
  Ian

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  jacques

  • December 26, 2014 06:25

  [quote="Ian3" wrote:
  The histogram is related to the output you get, and even with no edits the histogram may look different from what you see in the levels tool because it is affected by the ICC profile that is selected in the process recipe (on the output tab). Generally my process recipe is set to sRGB Color Space Profile. In that case the histogram does look different from what I see in the levels tool. But if I change the ICC profile in the process recipe to "Embed Camera Profile" the histogram changes and looks the same as in the levels tool.
  
  Ian

  
  
  Dear Ian,
  
  Thank you for your explanation, now I think I am starting to understand. Two more questions:
  
  1. When I change the relationship between the input and the output values in the levels and curve, none of the graphical representation of the levels and curve change but the histogram does. Is the following assumption correct: they do not change in order to keep seeing the "starting point" (a kind of "before" image) - sorry, I am not sure how to explain this; English is not my native language...
  
  2. How did you understand what you just wrote to me ? Out of experience or was it written somewhere in C1P's documentation ?
  
  Thanks again for your help

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  Ian Wilson

  Moderator

  • December 26, 2014 10:10

  

  Hi Jacques
  
  (1) Imagine that you do something like change the levels - perhaps you have an image with a limited range of tonal vales and you drag in the black point and the white point until they just clip the edges of the curve. The graph you see in the levels tool doesn't change - you just move the sliders. But that will change what you see in the Histogram tool and in the Curves tool. Before you moved the sliders, those graphs didn't fill the whole range from left to right, but now you will see that they do. So for example now when you use the Curves tool, the curve you set is applied to the graph you see in that window, rather than to the whole graph you had before you started.
  
  (2) I have picked up quite a lot of this from trial and error over the years. I've been using Capture One since version 4 (just as an amateur). But also I have watched videos in the YouTube channel, read the Image Professor's blog and things like that. The point about the Histogram being affected by the ICC profile I remember learning recently from another post in this forum.
  
  All the best.
  
  Ian

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  jacques

  • December 27, 2014 08:22

  Thanks Ian for your explanations. Hopefully this thread will help other people too.
  
  I really wish documentation about C1P was a bit more solid. Now that C1P is becoming more popular, who knows, a professional might want to write a book. Or maybe PhaseOne could work on their documentation instead of giving us new features for 8.2 😊

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