Levels sliders

Roy5

• 21 novembre 2008 00:30

I have been using the top and bottom levels sliders intuitively but I would like to know a little more about what they do. The bottom sliders seem to adjust the spread of exposure values to ensure the full range of 0-256 is being used. What then do the top sliders do? This subject is not covered in any tutorial as far as I can see.

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  Paul Steunebrink

  • 21 novembre 2008 08:15

  Good question. I think that since there is no written statement from the manufacturer, we all make up our own explanation. It is no rocket science though, 😉 but here is mine.
  
  As you stated, in the CO 4 Levels tool you have 3 sliders at the bottom (shadow - mid grey - high light level) and 2 at the top. The bottom sliders control the input levels (your 'exposure values' is a good equivalent term), as the top sliders control output levels (call it 'print values' if you like). The level tool's purpose is to control how input levels (a.k.a. exposure) are translated to output levels (a.k.a. print). Although you have only a few sliders to control the range of luminance from black to white, the values over the entire range adapt automatically and evenly when you adjust a slider.
  
  How to use? That very much depends on a number of factors. Some examples.
  
  Low contrast images need adjustment on the input side for either shadow level, highlight level or both to end up with a vivid image tone. Thanks to the rich amount of data in raw, you still get a continuous histogram in your RGB output file. The mid tone level adjustment is great for making an image brighter/darker without the risk of clipping your histogram as might happen with the exposure tool.
  On the output side, not all output devices get thrilled about a luminance values up to 255 or as low as 0 in your images: looks nice on screen but sometimes bad in print. To control and limit your output range, you use the top sliders. With your white point set with the bottom slider, you decide to translate that value to 240 instead of the default 255.
  
  The magic comes when you have some highlights clipping at the right of your histogram, you are able to recover them by adjusting the output level. With exposure warning turned on, you will see details recovered and the warning color disappear. I admit I did not use this technique, I used to adapt the exposure, use High Dynamic Range tool and so on. But I saw this in the Capture One tutorial video on Phase One's web site (). Worth visiting. Also consider to make presets for the levels tool. I have some with the mid tone slider in different positions. You can add output levels if you want to limit it to 5-250 for example instead of 0-255. Last but not least, check out the Preferences, Exposure. I you check the "Pick target levels" you can influence the output level of both the shadow and highlight pickers!
  
  Hope this helps.

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  Roy5

  • 21 novembre 2008 08:29

  Thanks Paul. That is a great explanation and I will have a look at the tutorial.
  
  Roy Ward

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