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Aperture showing clipping overlays when there isn't actually any clipping? #1
Kenneth Vinyaratn's picture
by Kenneth Vinyaratn
January 31, 2012 - 4:02pm

In Aperture (version 3.2.2, though it's been happening for well over a year and I just never got around to asking), I noticed something perplexing about it's white/black clipping overlays (View > “Highlight Hot & Cold Areas”).

I will say right away that my Preferences for “Hot Area threshold” and “Cold Area threshold” are at 100% and 0%, respectively - so that's not the problem.
(so at this setting, Aperture should only be highlighting clipping if RGB & Luminance levels are 0 or 255)

Since screenshots taken in OS X don't show the mouse cursor, I've uploaded a sample RAW file if you want to follow along as I'm describing it…
http://cl.ly/BoUD


The Aperture puts the white balance initially at 5487k and at this setting, the clipping overlays show “properly” - only pixels of 255 RBG/L values are highlighted as clipping.

However, I notice when I make a white balance adjustment, this doesn't seem to be the case, despite the setting in Preferences.

I'll use a more extreme example to illustrate my point…let's change the white balance color temp to 9000k. At this point, you should see a clipping overlay over the person's nose. However, if you mouse over the overlay on his nose, there are plenty if pixels that have not reached a 255 value that are highlighted as “clipping” (ie. R249 G224 B180 L226).


Any idea what's going on?

PhotoJoseph's picture
by PhotoJoseph
February 1, 2012 - 4:38am

Kenneth,

Interesting observation, and I can reproduce it.

It’s the red channel that’s clipping, although I can’t say why. If instead of using the Highlight Hot & Cold command, you press down the command key while adjusting (or just clicking on) the Exposure slider, you’ll see the same thing — but the channel that is blowing out will show in that color. Meaning if the red channel is blowing out, the overlay will be in red. [screenshot]

If you want more info on how that works, check out “Highlight Hot & Cold Areas… Command-drag or Toggle?”.

Red is close to 255, but not over, so yes it is odd.

I’ll report this as a bug and we’ll see what happens.

@PhotoJoseph
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Kenneth Vinyaratn's picture
by Kenneth Vinyaratn
February 1, 2012 - 7:10am

Thanks for your reply, Joseph!

I’ve posted this on 3 other forums and it’s got everyone stumped. But I’m happy to learn that trick to identify which channel specifically is clipping :)

PhotoJoseph's picture
by PhotoJoseph
February 1, 2012 - 8:41am

Kenneth,

From what I can see, it’s showing clipping when the red channel is over 250. That seems to be the consistent thread across everywhere it’s showing clipping.

Three other forums and no one got it yet? Glad to hear you got at least some good info from us ;-)

@PhotoJoseph
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