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Question about clipping display and histogram in ACR

Jul 19, 2012 5:59 PM

I have three questions about histogram in Camera Raw:

 

1) Sometimes I dont see any overexposed or underexposed areas on the histogram, but I can see it on the image whith shadow and highlight clipping function turned on. I am confused - is the particular area overexposed when the highlight clipping fuction shows it on the image or is it overexposed when histogram shows it?

 

2) Sometimes I dont see any shadow clipping on the image, but histogram shows it and it usually disappears only when I partially desaturate the image.

 

So there are obviously differences between clipping display on the image and the histogram. What are these differences? Sometimes I dont know what should I trust.

 

It seems the clipping display on the image shows when individual channels are clipped and the histogram shows only overal clipping. Am I right?

 

3) The third question is - is it bad  when only individual channel/color have reached max or min values? Or should I be concerned only when all channels (the overall luminance of pixels) are clipped?

 
Replies
  • Currently Being Moderated
    Jul 19, 2012 8:13 PM   in reply to hellboy801

    There are a number of issues with the display of clipping both highlight and shadow with ACR 7.1 - see this thread http://forums.adobe.com/message/4558412#4558412

     

    Eric Chan is looking into this and hopefully there will be some fixes soon. Originally it was thought that the display errors were shown and magnifications below 100% but I have examples which show there are display errors at 100%.

     

    At this time I do not trust the indicators nor some of the controls. For instance, with a hot highlight in a small area, adjusting the highlight control to the left (to dampen the highlight) actually increases the values and the clipping indicator grows - that is with all the other controls set to zero.

     

    Hoping the magic Eric can give an update soon

     

    Cheers

     

    Mike

     
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  • Currently Being Moderated
    Jul 19, 2012 11:16 PM   in reply to hellboy801

    Re shadow blocking... make sure you are not using sRGB as a working space,

    as some colors may simply be out of its gamut.

     

    Sent from phone.

     
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  • Currently Being Moderated
    Jul 20, 2012 4:52 AM   in reply to Dorin Nicolaescu-Musteață

    The issue is there regardless of color space. I normally use ProPhoto RGB, but see it with all the color space options in ACR.

     

    Mike

     
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  • Noel Carboni
    23,482 posts
    Dec 23, 2006
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    Jul 20, 2012 10:03 AM   in reply to Dorin Nicolaescu-Musteață

    Now we see once again why it was so awesome that Vit Novak crafted a special camera profile for me (and other Canon EOS-40D users) that squeezes the camera data so nicely into the sRGB color space. 

     

    -Noel

     
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  • Currently Being Moderated
    Jul 20, 2012 10:24 AM   in reply to Noel Carboni

    Noel:  Not sure whether it is the color space profile for the camera is the cause of this problem. I suspect there are some algorithm and display rendering anomolies that are in play here

     

    So far I think we have three issues:

    • Inaccurate display of shadow clipping at odd magnifications, especially at the intersection of a highlight and shadow area
    • Inaccurate display of highlight clipping
    • A highlight control that actually increases the value of a highlight instead of dampening it and that is with all the other controls set to zero.

     

    Looking forward to seeing an update from Mr. Chan

     

    By the way, even with custom camera profiles for my D3, D700 and D800 I see this problem regardless of color space

     

    Mike

     
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  • Noel Carboni
    23,482 posts
    Dec 23, 2006
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    Jul 20, 2012 11:01 AM   in reply to MikeKPhoto

    Mike, I wasn't implying that was the central issue to the clipping display anomalies, just that the burnout of channel data in shadows and blowout of channel data in highlights is just something I have to deal with way less with this custom profile.

     

    That said, I'm not seeing highlights and shadows indicator misbehavior, so it's possible the better-crafted profile is actually helping with this issue.

     

    -Noel

     
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  • Currently Being Moderated
    Jul 21, 2012 11:26 AM   in reply to Noel Carboni

    Situation show in the thread   http://forums.adobe.com/message/4558412#4558412   is normal for some camera profiles

     

    ACR is showing clipped areas (at least one of channels reaching maximum, as stated by Jeff) of RENDERED image, after applying the profile. And, some profiles can render a color which is blown in sensor color space to a color that isn't blown in output color space (sRGB for instance). BUT, the same hue which is slightly below being blow in sensor color space can be rendered into blown color in output color space. I attached graphical presentation of one hue segment of Canon 40D camera standard profile I sent to Noel a while ago (it is recalculated as effective raw -> sRGB lookup table + tone curve to show this, because actual transformation happens in Photo Pro color space). It is for hue 192 degree in sensor color space (cyan-blue) - there are 120 hue segments in total in that profile. So, applying highlights control can turn "nonblown" areas into "blow areas". But, there is nothing wrong with that - just one of the channels is at maximum, so don't be afraid to use this control when needed

     

    Reason for this is to somewhat improve the appearance of blown or near blown highlights in rendered image, which are the problem for digital sensors that have limited dynamic range, compared to negative film, and of course, dynamic range of output color space/device is also limited, compared to real scene. Even older Adobe standard profiles had something like this, but it was changed later. It's a matter of decision of producer of the profile (I mean Canon/Nikon etc and not producer of a camera profile for ACR, whether by Adobe or by my program or someone else, which is only a kind of back-engineering) how to render highlights to get best possible results / minimize issues in this area

     

    Only PV 2012 can use full potential of camera profiles (something built in Canon cameras years ago). In older ACR process models, highlight were unnecessarily clipped during whitebalancing and even recovery slider wasn't of much help with that

     

     

    40D sRGB.gif

     
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  • Currently Being Moderated
    Jul 21, 2012 4:41 PM   in reply to Vit Novak

    Thank you very much for this terrific post, Vit Novak.  Great job!

     
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  • Noel Carboni
    23,482 posts
    Dec 23, 2006
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    Jul 22, 2012 11:32 AM   in reply to Vit Novak

    Sheer genius.  Thank you again, Vit.

     

    -Noel

     
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