What is my histogram telling me?


TPF Noob!
Oct 11, 2008
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Fulton, Missouri
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My D80 has a histogram option in the display, and I get the basic idea of seeing what kind of exposure I'm getting with it. What do I really need to know about it? Any good links?
Keep the mountains away from the left (underexposure) and right(overexposure), don't worry about the middle.
The histogram is a very important tool to be used properly.

What is an histogram? Well, the histogram is a chart very simple to be read. On x-axis you have alla values from black to white, every dot corresponds to a specific value (0, 1, 2, 3, ..., 253, 254, 255)
On y-axis you can see how many pixels have got that specific value.
I try to explain better. Imagine to shoot in Black and White. The histogram tells you, from black (little numbers) to white (great numbers) how many pixels of your photo have got a specific grey value.

In general this is the histogram, a summary of how many pixels have got a specific value.
When you work with color photos you have 4 different hisotgrams: one for red channel, one for green channel, one for blue channel and one for all channels mixed, that's the one you should be looking at.

Be careful that the histogram CANNOT be referred, on the DSLR, to RAW pictures!! If you shoot RAW pictures, be careful that the histogram is telling you "lies". The histogram is realistic for TIFF or JPEG, but not RAW!

When you use a RAW file format you are managing a false image. Infact the RAW file doesn't contain an image, but it's only a summary with how many photons arrived on all sensor photosites. There's no color information in a RAW (until it's opened, for example, with Camera RAW), and so it's no possible to build the histogram of a RAW picture.

But when you shoot RAW (I hope you do it for real) you anyway see an histogram on your camera display. Why? What is that?
How I told you before that is a fake histogram, infact it referes to a SPECIFIC JPEG conversion made on-camera.
So you're not able to know which parameters have been adopted to perform this JPEG conversion, you cannot know the quality level, you cannot knwo too many things that you can manage when opening the RAW file with a specifica software (e.g. Camera RAW).
So the histogram tells you that, IN GENERAL, the amount of black and white is like the one you see on camera's display, but you can't be sure that it's REALLY THAT.

I wanna mean that if you shoot an underexposed picture you can understand it from the histogram of a RAW picture, if it doesn't contain white (if it doesn't touch the right limit of x-axis). But if you shoot a picture and it's histogram tells you that some light are blurred, this cannot be true, and you could be able to recover the lights via software processing.

So you have to learn to read the histogram on your camera, evaluating which is the limit of acceptable blurred lights. To do this you gotta shoot shoot shoot on and on, open the pictures with a specific software and try to understand this limit!

When using JPEG you have all another world. A JPEG is already an image, and for an image can be defined a valid histogram, that's the one you see on your camera, after the shot.
When working with JPEG you use an 8-bit conversion, that allows you to record values from 0 (black) to white (255), that's why I wrote previously 0 and 255 ad extreme values.
So if you see blurred lights on a JPEG histogram, you can be sure that those lights ARE BLURRED, so take another shot :D.

I see that other persons who replied to your question have linked an aspect that is very important in digital photography: exposure to the right!
My advice is that, after understanding what is an histogram, you should have to understand why it's better to adopt a right exposure.
for any questions... ask ;)

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