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The Histogram.....
Old 10-13-2004, 03:53 PM   #1 (permalink)
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OK... How do I tell when I am shooting by looking at my histogram that my exposure is good? I can tell you if its blowing out and if its all to one end or not but is there a tip on getting it dead on just by the histogram?

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Re: The Histogram.....
Old 10-13-2004, 05:00 PM   #2 (permalink)
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There was just a link to an article about reading histograms a few days ago. You might do a search on histograms and find the link. If not PM me and I will try to help you.

Michael

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Re: The Histogram.....
Old 10-13-2004, 05:47 PM   #3 (permalink)
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It really depends on what you are shooting.

I think the video for this product is a great place to start.
PhotoVision Calibration Targets
Watch the video of the 'How to' use the product.

Once you understand that you don't want any loss in data under 0 or over 255 on your histogram things will be easier to understand. Under normal circumstances there will be a peak in the middle sloping down to the 0 and 255 but not an enormous amount of data toward the ends.

Now.... You have a High Key background so you will have some 255+ portion of your histogram. I would shoot your model with your background lights off and see what the histogram looks like. Then shoot with you BG lights on and 1 to 1.5 stops over you main.

If you have already shot the image you can use the elliptical selection tool and select an area of the image and then look at the histogram to see if it is properly exposed. Someone on here explained this or posted a link to this technique. It was called the Facemask Histogram I think. The face being the most important part of a portrait it makes it easy to see if it is exposed properly.

Here is the article.....
Facemask Histogram

I hope this helps someone. The amount of wealth that I continually get from this site is never ending.

Take care,
Jim
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Re: The Histogram.....
Old 10-13-2004, 06:00 PM   #4 (permalink)
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Casey,

If you want the histogram to tell you "dead on" expsoure information, you need a standard to judge the histogram by. Unfortunately, just aiming it out the window or somewhere in the studio won't work, since all of your shots will be different.

What you CAN do is purchase one of the folding three-tone targets (see the Wescott ads... there are several different models, and other manufacturers, as well). Or, you can check out some of the books made for photogs and Photoshop - mine was "The Phtographer's Guide to Photoshop" or somesuch (I loaned the book out so I can't check right now), and it had a target in the back of the book (like this one, with Kristen from the Dallas GG workshop this summer):



Unfortunately, the one from the book was glossy, and so it reflects light directly (look on the bottom of the black and grey targets).

Or, you can make your own, using a matte finished black piece of cardboard, an 18% grey target from Kodak or one of the others, and a matt white piece of cardboard.

With these black, white, and a 18% grey target, you can line up your expsoure so that the histogram indicates a proper expsoure for that target... put the spikes for those colors in the right place on the histogram, and now you have something that, with experience, will help you judge whether your expsoure is on or not.

Do you have an 18% grey card already?

Wayne
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Re: The Histogram.....
Old 10-13-2004, 06:04 PM   #5 (permalink)
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I use a Canon Digital Rebel. There is a feature on the camera that shows the areas on a image that were blown-out. The camera shows this by blinking the areas.

So in using a white background, I would adjust the exposure on the camera so that only the white background would be blinking.

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Re: The Histogram.....
Old 10-13-2004, 07:47 PM   #6 (permalink)
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There is a good article here:

http://luminous-landscape.com/tutori...stograms.shtml
 
 
Re: The Histogram.....
Old 10-13-2004, 09:29 PM   #7 (permalink)
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I sometimes use the histogram on my camera to double-check my exposure of model's face when shooting portraits. My technique doesn't work in all situations with on-camera flash but does with off-camera flash and ambiant lighting.

I take a very close shot of just the models face and hair (making sure not to include much, if any background). The histogram should then not touch either the left (dark) or right (light) side of the display. If it does it indicates that I've got a bad exposure.

You can also do a similar thing in photoshop, by doing a marquee selection of just the face and hair and then looking at the Levels. The levels shown will be of just the selected area. See below.




Give it a try and see if it helps.


Mark Oehler
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Re: The Histogram.....
Old 10-13-2004, 10:08 PM   #8 (permalink)
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Actually the target card from the book will work just fine, but you need to fill the frame with the target. Then you'll see three spikes in the histogram (one on the left, one in the middle and one of the right) assuming that the exposure is proper. If you only see two, or the third one is clipped, then you adjust your exposure till you have three good spikes that are fully visible. I use the fold up (like a reflector) unit that is mentioned by one of the other posters but I also use the one from the book. It works like a charm.
When used as illustrated in your photo, you can make great use of Photoshop Curves and the three eyedroppers for exact color balance.

Here is another target for exposure use:



Cheers,
rfs
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Re: The Histogram.....
Old 10-13-2004, 10:36 PM   #9 (permalink)
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Yes, in actual use, the target card should (a) fill the frame and (b) be angled so that light is not directly reflected by the glossy cardboard. Your larger target thingie doesn't have that problem, of course.

But for purposes of identification of the product, I'd much rather see Kristen holding the card than just the card, itself, yes? [img]/ubbthreads/images/graemlins/laugh.gif[/img]

See ya on Sunday.

Wayne
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Re: The Histogram.....
Old 10-14-2004, 12:15 AM   #10 (permalink)
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yeah... but how much does that color card cost?
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