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Old Oct 9, 2003, 9:53 PM   #1
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Can someone explain to me how to use a histogram and its significance? I've read a few articles, but I'm not getting it. THX!
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Old Oct 10, 2003, 3:52 AM   #2
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This article should make it clear:
http://www.dpreview.com/learn/Glossa...stogram_01.htm

I don't know how to explain it more clearly than that.

It does assume basic knowledge: you know what a pixel is and what an intensity level (brightness) of a pixel is (either in RGB or luminence). If you are missing that background, please read up on that first and then the histogram and what you can do with it will start to make sense to you.

Good luck
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Old Oct 10, 2003, 5:17 AM   #3
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The histogram on its own needs to be interpreted agains the actual scene to be of use. Scenes rarely fall into the average 'bell shaped' distribution of light and dark. The most useful feature is to indicate highlight(and lowlight) clipping (high peaks at the right hand white end (and left hand black end).

Unfortunately the histogram does not tell you actual location in the pic where highlights are clipped - only how many high values there are. So to be useful, if you have white dresses or a lot of sky in a scene, you assume the highest values will be these parts and then can decide whether to underexpose by say a stop (possibly accepting a tad more noise), or accept the burn out if it's only darker close up foreground and not highlight detail you are interested in.

Clipping destroys detail and is the most annoying problem caused by limited brightness range handling. It is almost impossible to see in the EVF or lcd, clearly obvious afterwards on a monitor or prints and impossible to recover lost detail afterwards.

Practice using the histogram on different scene types, whilst modifying 'auto' exposure settings and look at the results. Because when all you have is the scene the camera and a histogram, it will be help you avoid over exposed highlights or auto exposure getting it wrong.
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Old Oct 10, 2003, 6:39 AM   #4
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Some Nikons (e.g. the CP4500 and the D100) will also show you any burnt out highlights during image review. However, for safety I go for slight under exposure and then correct it in your digital darkroom.
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Old Oct 10, 2003, 6:46 AM   #5
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here in living color. and it tells you a lot and where once you grab the concept.

http://luminous-landscape.com/tutori...stograms.shtml
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Old Oct 10, 2003, 7:30 AM   #6
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... Also don't forget some EVF based cameras have the histogram in REAL-TIME as you adjust the settings on the cameras!
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Old Oct 10, 2003, 11:01 AM   #7
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Yes, and most prof. TV cams have 'zebra' which in real time wiggles a pattern over any area of the scene which hits the white clipper!

That link you posted sjms says it all. Now everybody can get a flavour of what Fuji are trying to do with their new cams to extend the dynamic range, and how in the link the prospect of overlaying two shots might work - EXCEPT when something moves!
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Old Oct 10, 2003, 2:29 PM   #8
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THX everyone. I'll read up on this info over the weekend and make another post if I'm still confused. Best - john
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Old Oct 12, 2003, 7:56 PM   #9
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I think I've got it. The pattern in a histogram is not necessarily a direct correlation of the photo lay out - that's what was confusing me. It's a pattern tool of the entire image and can be rearranged depending upon the characteristics of the shot. I'll start using it when I shoot and comparing it to my properly and improperly exposed photos. THX!
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Old Oct 13, 2003, 2:40 AM   #10
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I have been working with histograms (not just in photography) for so long that it is sometimes hard to understand what the difficulty can be when someone is introduced to the concept.

It looks like you got it right now, fporch. There is NO correlation between the histogram and the photolayout by definition. In fact, you can randomize all pixel locations (getting a random noise picture) with exactly the same histogram. However because we tend not to photograph random noise, there actually is correlation (like the supplied links show, it can be used to highlight section of the image that are overexposed for instance). So you will find the pixels that contain "air" in the scene, in the higher regions (the right part) of your histogram.
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