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Incorrect exposure indicator - is there one

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  #1  
Old 09-16-2005, 05:29 PM
Nacoya Nacoya is offline
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Incorrect exposure indicator - is there one

Hi,

I wondered if there is a plugin for photoshop which will show areas of under or over exposure in a photo. I know that in certain filters in powerretouche pro there are black and white exposure boxes to tick to indicate areas of incorrect exposure. Even my camera flashes areas of incorrect exposure (but only after the pic is taken ). So i just wondered is there was an individual plugin to show this.

Or am i barking up the wrong tree.

cheers,

nacoya
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  #2  
Old 10-03-2005, 01:44 AM
berwin berwin is offline
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Use Alt+Levels

When checking for over- or under exposure in PS, you can call up the Levels either as layer or as adjustment and do the following:

Hold the Alt-key while either grabbing the rightmost (white) triangle slider and moving it to the left, or grabbing the leftmost (black) slider and moving it to the right. This will invoke a 2 bit image(either white or black, showing the thresholds).


While holding the Alt key:
What you will see if overexposure is present, is an area of white-outs as you touch the rightmost slider and begin to move it left. Conversely, if underexposure is present, you will see an area of black-outs as you touch the leftmost slider and begin to move it right.


While holding the Alt key:
If properly exposed, and either moving the leftmost slider(shadows) right or moving the rightmost slider(highlights) left, you will see a threshold of either blacks or whites respectively cutting in, indicating the setting of the minimum(shadows) or maximum(highlights) levels adjustment before clipping shadows or highlights. For properly exposed images, this can be a method of maximizing the histogram, ensuring a good rendition of blacks and whites without black blocking or white blowouts, by not allowing either.
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Old 10-03-2005, 11:46 AM
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byRo byRo is offline
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Nacoya,

If you just want to know which areas of the photo are at the extreme values (0 or 255) then you don't need a plug-in - you can use a curves layer to make a "clipping detector".

- Make a new curves adjustment layer;
- Change the curve drawing mode to the pencil, not continuous curves;
- For each of the three colour curves....
-- At 0 put in a dot at 255;
-- At 255 put in a dot at 0;
(save this as a curve, or better still as an action)

Now everything that is at 0 or 255 will get inverted, if some pixel has red max'ed out it will come out as cyan.
Works the same way as the clipping detector in PS's Image>Adjust>Variations.

Shame I don't have PS here, or I could have posted it. I'll send it from home tonight.

Ro
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Old 10-03-2005, 11:53 AM
Ken Fournelle Ken Fournelle is offline
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Ro,

Doesn't making a Levels Adj. Layer and then while depressing the Alt/Option key, click and move the sliders do much the same thing?

Ken
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  #5  
Old 10-03-2005, 06:07 PM
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Doug Nelson Doug Nelson is offline
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Assuming you mean clipped areas rather than incorrectly exposed areas (I can't imagine any computer let alone any software that could judge "correct" exposure), Adobe Camera Raw has an option box that can be enabled to show clipped areas.
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Old 10-03-2005, 06:48 PM
Ken Fournelle Ken Fournelle is offline
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Yes, Doug, I meant clipped areas.

k
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  #7  
Old 10-03-2005, 07:39 PM
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byRo byRo is offline
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Quote:
Originally Posted by Ken Fournelle
Ro,

Doesn't making a Levels Adj. Layer and then while depressing the Alt/Option key, click and move the sliders do much the same thing?

Ken
Yes, but......
1)...using the Clipping detector as a layer you don't need to move anything - if you use the action posted below just one click will suffice;
2)...you can leave the Clipping detector as the top layer and ensure that any modifications you make aren't introducing (more) clipping.

The advantage of the Levels + Alt would be in cases where clipping has almost ocurred (levels 1 or 254), however a quick look at the histogram might still be a better option.

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File Type: jpg face-byRo-no-detect.jpg (99.6 KB, 15 views)
File Type: jpg face-byRo-detector.jpg (99.6 KB, 18 views)
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File Type: zip byRo Clipping Detector.zip (1.0 KB, 29 views)
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  #8  
Old 10-03-2005, 10:06 PM
Ken Fournelle Ken Fournelle is offline
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Very nice. The amazing Ro strikes again.

Thanks for the action!

k
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  #9  
Old 10-04-2005, 08:25 PM
Nacoya Nacoya is offline
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excellent thanks byRo. I'll have a go with that tomorrow..i'm starting a collection of byRo actions. (well this is no.2 )

cheers.
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  #10  
Old 10-06-2005, 06:52 PM
Nacoya Nacoya is offline
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Hi folks,

Sorry not to get back sooner but i was building my new PC (he says with a huge grin). I have now tried your action byRo and had a tweak with berwins adjustment (although i suspect i'm missing something). I used the attached image (which i've had to really compress to get under 100k) as I was sure that the sky was overexposed. It was a white sky kinna day when I took it, but neverthless. But both methods tell me that it's not. It's very close to being overexposed but not the blow out I originally thought when i first glimpsed at it..

Thoughts please ..

cheers,

nacoya
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