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Histograms?
Old 04-04-2005, 09:04 AM   #1 (permalink)
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I know what a histogram is from math class. Unfortunately, I don't know what I'm supposed to do with it in regards to a photo.

Is it supposed to be a bell curve, or all over the damn place like most of mine are? Is the histogram in my Nikon D100 the same as the one that Photoshop produces? If the histogram isn't right, what do I do to fix it?
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Re: Histograms?
Old 04-04-2005, 09:34 AM   #2 (permalink)
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Shootsmarter.com has a good article on histograms. Link requires registration, but it's free and they have great articles.

Facemask Histograms on Shootsmarter.com

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Re: Histograms?
Old 04-04-2005, 10:57 AM   #3 (permalink)
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Nikon histograms only display the green channel. It will be different from Photoshops histogram depending on how much green is in the picture. See a better explination here.

http://www.kenrockwell.com/nikon/d70...tm#performance
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Another good tutorial on understanding Histograms
Old 04-04-2005, 11:32 AM   #4 (permalink)
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This is a pretty good article to read on histograms
Understanding Histograms By Michael Reichmann

Hope that helps

Bill
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Re: Histograms?
Old 04-04-2005, 11:38 AM   #5 (permalink)
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The histogram is one of the things that makes digital photography so exciting and opens a whole range of new techniques. The histogram gives you a graph of the distribution of tonal values in your photo. The left side shows the amount of the photo that is in the shadow area. The middle shows the amount of the photo in the mid tones area and the right side shows the quantity of tones in the highlight area.

If you use a gray card, and shoot a photo of it full frame, then you would expect to see a histogram with one big spike right in the middle and nothing else. This would indicate good exposure. But if the spike is not centralized, then you know the exposure may be a little off and you can shoot the gray card again at a different exposure setting to move the spike around.

I actually use a black/gray/white card which produces three spikes. Your goal is to get all three spikes showing at the same time and then you adjust expousre to move them as far right in the histogram as you can without clipping the spike on the right. In this manner you can get spot on exposures which is very critical for digital photography.

The histogram in Photoshop and the one in the camera may not match, so it is important to shoot a number of shots of the black/gray/white card where you have clipped and non clipped test photos and then you examine the histogram of each in PS while comparing it to the camera's histogram. In this manner you, in effect, calibrate the histogram of the camera so you know how to read it properly visa via Photoshop.

Cheers,
rfs
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Re: Histograms?
Old 04-04-2005, 02:26 PM   #6 (permalink)
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http://www.sphoto.com/techinfo/histo...histograms.htm
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Histograms?
Old 04-04-2005, 07:40 PM   #7 (permalink)
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I use it all the time and I believe that if you do too, you will be happy with the exposure of your photographs right out of the camera.
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Re: Histograms?
Old 04-06-2005, 01:05 PM   #8 (permalink)
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first off, you should never rely on a histogram to calculate your exposure. that's what light meters are for. light meters are ESSENTIAL to photography, and even more so with digital.

histograms are useful for checking exposures after getting your base exposure with a light meter, because histograms represent the global tonal values present in the frame, but it doesn't indicate if the most important element is properly exposed. you could be way off with your exposure and not know it from the in-camera histogram. the best way to use a histogram is in Photoshop where you can isolate exactly what you are exposing for via selection tools and the histogram that applies to that selection for your critical exposure.

a histogram is merely a guide. exposure is best calculated using a good incident light meter, which will measure light in 1/10's of a stop. i'd like to see a 1/2 inch histogram do that. and what could be easier than pressing a button and getting all the info you need, rather than fiddling with your shutter speed and aperture dials trying to move a graph around, which still wouldn't be the correct exposure 99% of the time?

nothing beats using the right tools for the job.
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Re: Histograms?
Old 04-06-2005, 05:35 PM   #9 (permalink)
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Actually you can determine the exposure very precisely using the camera's histogram. This is possible with a gray card, but for even more precise results just use a Black/Gray/White card. I've outlined the exact method several times in other posts, so you can check those out if you're interested. I've been using these methods for years and they work perfectly.
If you do choose to use an external incident light meter, then for digital photography it is essential that you properly calibrate its readings for the camera. This is usually done using the above mentioned cards. I've found that virtually every meter I've looked at can give exposure readings that are off by as much as 2 stops, especially when using a digital camera.
Cheers,
rfs
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