Aperture showing clipping overlays when there isn't actually any clipping?

[PkennethV]

Hi everyone,

In Aperture (version 3.2.1, 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).

Why is this

 

[PkennethV]

I know bumps are frowned upon, but it's been 2 and half months...anyone?

 

[TheDrift-]

First off let me say this is pure guess work on my part, so please dont take this as anything more than a Guess

At daylight white balance the clipped part of your image is showing 255, 255, 255

So far so good...

When you increase the temprature to as you say 9000k the colour values change to 249 224 & 180..but the area still shows as clipped..

The area is still clipped IE contains no other information than the pure white 255,255,255 values, but in order to show the colour shift associated with warming the image, it must introduce colour to the white to make it warmer....mainly in will need to decrease the blue's to increase the yellows (opposites on the colour wheel) this appears to fit with your figures showing the blue most reduced.

...so the area is clipped, the clipping mask is showing it clipped, all you are doing by shifting the WB is artificially putting colour in the 255 white so it's not 255 white anymore..but fundamtentally its clipped and there is no info there...(well maybe if its raw and you try curves, levels, recovery slider etc, but you get the point.)

Hopefully that makes a bit of sense????

 

[PkennethV]

Thanks for your reply, TheDrift-

I think I understand what you are suggesting, but (unless I've misunderstood something) it doesn't quite add up to me...

From what I understand, you are saying that for areas that were originally clipped to begin with, if I made a WB adjustment that introduced "artificial" color (which makes the area no longer appear to be pure white), Aperture will still show the clipping overlay to let us know that there is no "real" information in that area - it's still, in reality 255.

If that's what you are saying, it makes sense (and is a great feature), but I don't think that's really the "phenomenon" that I'm describing.

Because in what I'm describing, with a WB adjustment, I can actually introduce more areas where the clipping overlay would cover vs the out of camera RAW file.

In other words, there is less "clipping" occurring (according to the overlay) at the original 5487k WB setting of that picture, than there is at 9000k. Those "new" areas marked as clipping at 9000k are not showing 255 values.

 

[TheDrift-]

Thanks for your reply, TheDrift-

I think I understand what you are suggesting, but (unless I've misunderstood something) it doesn't quite add up to me...

From what I understand, you are saying that for areas that were originally clipped to begin with, if I made a WB adjustment that introduced "artificial" color (which makes the area no longer appear to be pure white), Aperture will still show the clipping overlay to let us know that there is no "real" information in that area - it's still, in reality 255.

If that's what you are saying, it makes sense (and is a great feature), but I don't think that's really the "phenomenon" that I'm describing.

Because in what I'm describing, with a WB adjustment, I can actually introduce more areas where the clipping overlay would cover vs the out of camera RAW file.

In other words, there is less "clipping" occurring (according to the overlay) at the original 5487k WB setting of that picture, than there is at 9000k. Those "new" areas marked as clipping at 9000k are not showing 255 values.

Ok I very rarely, if ever use a clipping mask...

In camera Raw the instead of taking blue away to make it shift yellow, they add red and green (which has the same effect) this makes the image much brighter and introduces clipping..

In aperture things seem to work a little different (aperture seems to both add colour and take some away), it also seems to hold off on actually clipping, as it stops just shy, around 252/253 but does loose detail...I tried an extreme cooling of an image which introduced a massive blue spike just shy of clipping, decreasing the exposure dragged loads of detail out of this spike.

So you are losing more detail and the clipping mask is showing this..but why it is telling you this at 252/253 when you ask for 255 is a mystery, you could try sampling points in aperture then export to say photoshop and see if that tells a different story?....seems a bit overkill to me...I'd just put it down to one of those things?