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Savannah
05-02-2005, 10:24 PM
Could somebody give me a lesson on how to read histograms?? Just the cliff notes will be okay. Thanks.

TheObiJuan
05-02-2005, 10:33 PM
This site is really good. It provides pictures for those who need visuals. It is a simple, yet good read.
http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml

Essentially, when the histogram is bunched up to the far right, you are overexposing, to the far left, underexposing. When the far left or far right values are to the roof, you have clipped shadows or highlights. When the middle hump is too scrunched and hight,there is not enough contrast and not enough midtones. Usually this will yield a washed out image.
Here is another link:
http://www.dpreview.com/learn/?/Glossary/Digital_Imaging/Histogram_01.htm

Modifying my image and keeping a close eye in photoshop helped me learn too.

Rex914
05-02-2005, 10:42 PM
In my own words, I'd describe a histogram as a graph that plots every pixel in a picture and sorts them from "lightest" to "darkest."

Remember histograms in statistics class? Or do you remember from college how the professor would graph out the grades on an exam in a histogram? That's the kind of graph it is.

A histogram is used to determine whether you properly exposed a photograph. While the following rules don't apply in every case, they do work in most normal situations.

1) If you look a histogram and you see a lot of values clumped up on the right (light/white side), that's overexposure. You probably know this from experience since overexposed photos are too bright and have blown out white highlights. That makes sense because there is a disproportionate number of "light" pixels.

2) On the other hand, if all the values are clumped on the left side (dark/black), you have underexposed the photo. An underexposed photo usually appears darker than normal. In general, it's safer to underexpose than to overexpose since it's easier to correct for that.

3) If there's a nice even spread throughout, you've got a properly exposed photo.

4) If your values are clumped up in the middle, and if the edges have nothing, chances are your photo needs more contrast. On the flipside, if the values are on the edges and not in the center, the photo may have too much contrast.

In the end, reading histograms to determine proper exposure is pretty easy, once you get these general principles down. It's only in the tricky cases that you really have to understand what's going in the photograph to determine whether the graph is telling the truth or not. Here's a situation like that:

Take a look at this picture and the histogram. Looks far underexposed doesn't it?

http://www.gotosnapshot.com/digital-slr/d-images/Histogram2-Anemone.jpg

Nevertheless, this is a properly exposed photo if you read the graph carefully. That huge spike is actually accounted for in that black background.

In most cases, you can blindly read histograms, but if you come across a strange one like this one, just keep the situation in mind, and you'll know how to approach it.

I hope this short summary helps.

Savannah
05-04-2005, 02:10 PM
Thanks to both of you. This has been very helpful. I've been using the histogram to help me take better photo's now. It's a very valuable tool. I appreciate you both for being generous with your time to answer my question. The links are a wealth of information! Thanks so much!!

Stacy

Jredtugboat
05-04-2005, 02:28 PM
This site is really good. It provides pictures for those who need visuals. It is a simple, yet good read.
http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml

Essentially, when the histogram is bunched up to the far right, you are overexposing, to the far left, underexposing. When the far left or far right values are to the roof, you have clipped shadows or highlights. When the middle hump is too scrunched and hight,there is not enough contrast and not enough midtones. Usually this will yield a washed out image.
Here is another link:
http://www.dpreview.com/learn/?/Glossary/Digital_Imaging/Histogram_01.htm

Modifying my image and keeping a close eye in photoshop helped me learn too.

Thanks for the primer. I've glanced at mine and more or less understood them ("too left, too dark; too right, to bright").

Julian

Jredtugboat
05-04-2005, 02:30 PM
Take a look at this picture and the histogram. Looks far underexposed doesn't it?

http://www.gotosnapshot.com/digital-slr/d-images/Histogram2-Anemone.jpg

Nevertheless, this is a properly exposed photo if you read the graph carefully. That huge spike is actually accounted for in that black background.

In most cases, you can blindly read histograms, but if you come across a strange one like this one, just keep the situation in mind, and you'll know how to approach it.

I hope this short summary helps.

That's a very nice example there, the anemone. I'd often wondered about that sort of thing when I had histograms that read something like that. Most often they were underexposed, but then I have some indoor stuff of subjects in low light with big, black backgrounds...thusly explained...

Thanks,

Yours,

Julian