6 Replies Latest reply: Oct 16, 2012 7:11 AM by papalapapp
papalapapp Level 1 Level 1 (80 points)

The Aperture manual says:

 

  • Auto adjust White Clip slider: Use the “Auto adjust White Clip” slider and value slider to add tolerance to Auto Levels adjustments when evaluating colors beyond white.

 

But I don't know what they mean with "add tolerance". What is it intended to do?


MacBook, Mac OS X (10.7), 2 GHz Core 2 Duo 1TB + 256 GB SSD
  • Kirby Krieger Level 6 Level 6 (12,500 points)

    "Auto Levels" analyses your Image and applies a Levels adjustment based on a preset algorithm (similar to "Auto-enhance" in iPhoto, for example).  The Auto adjust White Clip slider allows you to set what percentage of pixels will be set to full-luminance.  (Hover your cursor over the slider for a ToolTip.)

     

    This is very easy to see in practice.  Select an Image with no adjustments applied, and duplicate it.  Then with the Auto adjust White Clip slider set to the left, click "Auto" in the Levels Brick.  Select the other Image, change the slider all the way to the right, and "Auto-Levels" that Image.  Compare the two.  Be sure to compare the histograms in the Levels Bricks: this shows you mathematically what the difference is.

     

    Message was edited by: Kirby Krieger -- clarifications.

  • papalapapp Level 1 Level 1 (80 points)

    Thanks for your help. Unfortunately the tooltip isn't any help in my language. (Also the label of that slider only says "Auto-adjust white areas".)

     

    So, do I understand it right that if the value is set to 10%, the top 10% of the white pixels will be set to maximum luminance (the curve moves slightly to the left)?

  • Kirby Krieger Level 6 Level 6 (12,500 points)

    Sorry about the useless ToolTip.  Send a note to Apple requesting complete localization:  "Aperture➞Provide Aperture Feedback".

    papalapapp wrote:

     

    So, do I understand it right that if the value is set to 10%, the top 10% of the white pixels will be set to maximum luminance (the curve moves slightly to the left)?

    Pretty much, but a couple of notes.

    • "Maximum luminance" is generally accepted to be equal to "white".  I assume you mean "the top 10% most luminant pixels will be set to maximum luminance".

    • I don't know what formulas are used, so I can't put an actual number to the effect.  The effect is (again) easy to see in comparison.  Just make two Versions, use "Auto Levels" on each, but use a different setting in the Prefs for each, and take a look.

  • papalapapp Level 1 Level 1 (80 points)

    Thanks for these useful explanations. I think now I know how to use it.

     

    I compared some different photos after your first post. Those with no obvious white areas seemed brighter when the preset was set to 10 compared to 0. And those with a lot of white space (tabletop with white background) had a better "burnt out" pure white background.

  • Kirby Krieger Level 6 Level 6 (12,500 points)

    Remember that the sliders determine how the "Auto-Levels" function works.  You can always use Levels manually, and/or make further adjustments after applying "Auto-Levels".  To get the same effect as setting the slider to a high value, click and drag the white point handle at the bottom of the histogram to the left.

  • papalapapp Level 1 Level 1 (80 points)

    Thanks Kirby, that's what I usually do for white backgrounds. Turn up the contrast, brightness and then drag the white point to the left.

     

    But I think, with this slider preset, the auto-value button might be a handy shortcut to a kind of pre-optimised adjustment. I'll need to play around with it a little bit more.