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10-22-2009, 09:19 PM   #1
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Histogram.....what is this? >_<


Today i went on google and typed the dreaded thing : Reading Camera Histogram.
I came to two articles, out of which all I understood was that the histogram is always dark on the left, bright to the right.

What now?

I am not sure i understand the application of it, despite many claims of how it is an important tool.
Take the landscape example :
Understanding Your Digital Camera's Histogram (2) -- A Nikonians Guide

I actually liked this underexposed picture that would have looked problematic on the histogram. It really highlights the clouds?

on the next page, Understanding Your Digital Camera's Histogram (3) -- A Nikonians Guide , i actually didnt like this slightly overexposed picture. :ugh:

What if you, as a photographer, like underexposed images, or harsh lighting? Taking pictures of dark corners and street shadows...wouldnt they all be unbalanced in the histogram?

My problem is :

1. Why should you read a histogram to figure out whether the picture was too dark/too bright, when the actual picture is previewed in your viewfinder? Or you shouldnt, and i am just catching up to a thing of the past?
2. Why should you read a histogram if you can do HDR say in PP?
3. If the histogram is clipped to the left (too dark), i should increase lighting, or slow down my shutter speed, or increase my exposure, or increase my aperture....I do all these things if i see the picture preview as being too dark. Is there something else that reading a histogram does that i cant make without?

I guess some starters as to when and why i should be using histogram would be good...and if there are any, what would be the ideal histogram graphic be?

10-22-2009, 09:38 PM   #2
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If you shoot in JPG, there is less margin to pull the image back with PP, so a histogram and image review is useful. Also nice to get it right at the camera when you don't want to PP lots of images.

The ambient light on bright days can fool you when you review the image on the camera screen. A histogram isn't affected much by the.viewing conditions.

All of that said, I have been using DLSR's for four years and only recently started to see the usefulness of histograms in the camera.
10-22-2009, 09:48 PM   #3
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Quite a heavily discussed topic mainly for people's misconceptions about its use.
Histograms are a great guide, but a poor means of 'telling' whether a photo is under/over-exposed. It's not as simple as looking at the histogram and seeing that all the pixels register within the graph's range. Interpreting the histogram means knowing what you're shooting, what will register in the low and high key and exposing FOR THE SUBJECT.

To save from going over a lot about histograms again, I'll just refer to previous threads about similar issues:

https://www.pentaxforums.com/forums/general-photography-techniques-styles/500...histogram.html

https://www.pentaxforums.com/forums/general-photography-techniques-styles/474...confusion.html

https://www.pentaxforums.com/forums/pentax-dslr-discussion/74913-what-constit...-exposure.html

https://www.pentaxforums.com/forums/pentax-beginners-corner-q/73310-using-histogram.html
10-22-2009, 10:28 PM   #4
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Thanks guys! i am reading these materials, i am going to start turning on my histogram and see if i can get a pattern i can recognize (after reading some of those posts, i took a look at histogram info of one of my pictures that wasnt too bright nor too dark, and all i got was a flat really low line that peaks out at bright. totally confuses me, lol)

10-23-2009, 03:38 AM   #5
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Here are more good articles on histograms Understanding Digital Camera Histograms: Tones and Contrast

The histogram will tell you more about the exposure than the screen image will, especially in daylight. Remember that images which are clipped on the left will display noise if you try and lighten them in editing software (pp), and clipping on the right means you have not captured those tones at all and will appear "blown out" whatever you do in pp.

For a general scene with dark and light tones and a majority of mid range tones you will get the classic bell curve if you expose correctly.

However if you want a silhouette look to a particular shot then you dont want to try and achieve that bell curve histogram. You will want the histogram to be lumped up against the left edge with a narrow strip running to the right.

Conversly if you are after a "high key" picture, your histogram should be biased to the right, but with minimal clipping.
10-23-2009, 06:05 AM   #6
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Thanks Those have a lot more graphics for me to compare to.
10-23-2009, 10:11 AM   #7
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The histogram is simply a quantification of something that you can judge (with varying degrees of accuracy) with your eyes as well... just that "human judgement" varies (even for the same subject, depending on environmental factors)... but the histogram is "machine generated" therefore less volatile...

I would say that the histogram is not something to be "adhered to" but more of a guide to set better expectations when you get the pic onto the pc. If you are unsure whether the shadows are too dark (and there is just that much that can be judged through the viewfinder) and not sure if you may loose some detail that your eyes (without viewfinder) can see... a test shot and the resulting histogram can help quantify things... vice versa for the 'right side' shots...

And as pointed out earlier, it gives you an indication of what can or cannot be salvaged later (through PP) and may convince you to take a few extra shots with different settings, just to be sure...
10-23-2009, 10:15 AM   #8
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Personally I prefer the warning "blinkies" more than the histogram. The histogram tells you something is blown. The warning tells you what.

10-23-2009, 12:31 PM   #9
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QuoteOriginally posted by graphicgr8s Quote
Personally I prefer the warning "blinkies" more than the histogram. The histogram tells you something is blown. The warning tells you what.
I'll second this observation, as I tend to utilize the "blinkies" for what is blown out.

However, one feature I've enjoyed recently is the option to view each channel's histogram. That is quite useful when you may blow out one channel specifically, which won't show up in the "blinkies".

I also rely on the histogram to be sure I'm not underexposing something more than I might like and/or if I end up shooting for HDR.
10-23-2009, 01:45 PM   #10
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First, let's review what a histogram actually is. It's a graph that shows the relative distribution of lighter and darker pixels in the photo. The x-axis or horizontal axis represents different shades of light and dark, like this. At the left side of the axis are the darkest pixels, and on the right, the lighter and lightest pixels. If you set your camera to ISO 1600, f/2.8, shutter 1/8th sec and took a close-up photo of a bright light bulb, the histogram would be all crammed up against the right side of the graph. If you take a photo in a dark room at night, the data colums will be shoved way up against the left side of the graph. Take a photo outside on a cloudy but otherwise reasonably lit day, using your camera's auto exposure mode, and you'll probably see a classic bell curve, with most of the data somewhere near the middle of the graph, and more data tapering off to the left or right. Finally, every now and then you can take a photo of something with extremely high contrast - say, a groom in a black tuxedo standing against a brightly lit white wall - and the histogram might have two sharp peaks and a lot of blank space between them.

The histogram doesn't tell you whether the photo is correctly exposed. It just tells you how the shades of light and dark are distributed.

Sometimes, a histogram that leans sharply to the right ("over" exposed) side of the graph is in fact exactly what you would want. You have to overexpose, for example, to get the bride's white dress to appear white in the photo. Perhaps in doing so you blow out a bit of the sky - that might be okay.

The histogram is most useful if you use it in conjunction with the "bright/dark" display feature on your camera - the feature that causes blown highlights and lost darks to blink so you can tell WHERE you've lost useful data. If you blow highlights where they don't matter, you can ignore the histogram.

The dynamic range that the camera can capture in a single shot (somewhere around five stops) is considerably less than the dynamic range of reality as we perceive it. If your lighting is fairly even, you can usually get the exposure set so that the histogram doesn't run afoul of either the right limit or the left. In that case, you'll have a histogram that doesn't touch either side of the graph. And when that happens, it's best to push the histogram as far to the right as possible. Why? Because the camera's sensor is more sensitive - makes finer distinctions between shades - at the bright end than at the dark end, or to put it differently, the number of distinct shades represented by the right side of the histogram is MUCH greater than the number represented on the left. Hence the advice given by the famous "expose to the right" article at Luminous Landscape that somebody has already linked to. NOTE that this is not a matter of opinion or artistic judgment. It's a fact about how digital sensors work. Doesn't apply to film photography. This is one of the important ways in which a really experience film photographer would have to learn to think just a little differently in order to take maximum advantage of a digital system.

Sometimes, however, the dynamic range of the scene is too great for you to capture the darks AND the lights properly. Then you have to decide what you can afford to lose and what you can't afford to lose and adjust your exposure accordingly.


QuoteOriginally posted by D4rknezz Quote
What if you, as a photographer, like underexposed images, or harsh lighting? Taking pictures of dark corners and street shadows...wouldnt they all be unbalanced in the histogram?
Nobody likes underexposed images. "Underexposed" is by definition a fault. However, you're thinking that underexposed means that the histogram is way over on the left. That's not correct. I'll say it again: the histogram is descriptive, not prescriptive. It doesn't tell you what to do. If the photo looks right on the computer screen or when printed, it doesn't matter that the histogram leans to the left. The test of underexposure or overexposure is the human eye, not the histogram.


QuoteQuote:
1. Why should you read a histogram to figure out whether the picture was too dark/too bright, when the actual picture is previewed in your viewfinder? Or you shouldnt, and i am just catching up to a thing of the past?
See what I said above - but I'll say it again a bit differently. In order to take maximum advantage of your digital sensor, you want to push the histogram as far to the right as possible. "As far as possible" means "without blowing significant highlights." The result of this - ironically - is that in some cases, when the dynamic range of the photo is fairly small, a correct exposure may actually APPEAR INITIALLY to be an overexposure. Meditate on that for a while!

(As a practical matter, this happens less often than you might expect, and when it does happen it happens less dramatically. Why? Because the majority of the photos that most of us take are NOT so limited in dynamic range that we can afford to push the histogram too far to the right.)


QuoteQuote:
2. Why should you read a histogram if you can do HDR say in PP?
I don't understand the question. Don't see what one has to do with the other. If you're doing HDR, you will still want to have a carefully exposed original capture.

QuoteQuote:
3. If the histogram is clipped to the left (too dark), i should increase lighting, or slow down my shutter speed, or increase my exposure, or increase my aperture....I do all these things if i see the picture preview as being too dark. Is there something else that reading a histogram does that i cant make without?
No, you're thinking of it simplistically. Just because the histogram leans up against the left side of the graph does NOT mean that you should increase the exposure. If the histogram also shows data well distributed on the right side of the graph, then your exposure might be correct. What you would usually NOT want is a histogram that ONLY shows data on the left side and is entirely blank on the right.


QuoteQuote:
I guess some starters as to when and why i should be using histogram would be good...and if there are any, what would be the ideal histogram graphic be?
NO answer to that question. There is no ideal histogram. The histogram says more about what you want to avoid than about what you should try to achieve.

Will
10-23-2009, 02:04 PM   #11
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A fairly good instructive article on understanding a histogram can be read here

Understanding Histograms

I agree with others that a lot of this will come down to the image being taken and the photographer's intent of the image.

While there is not such things as a perfect histogram, it does serve as a good tool in the field to quickly evaluate a photo from a technical standpoint and where it might go in post processing.
10-26-2009, 03:16 PM   #12
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Given the generalness of the questions asked, you may be better off getting a book like "Understanding Exposure" by Brian Peterson to give an idea of what exposure is about in general. That will help you get a handle on what exposure is and how you might translate that will help you out with understanding histograms.

It doesn't address histograms directly, but there are some great examples about how to set up exposures, exposure compensation, and how your camera tries to interpret a scene.

I think one of the best examples that is often used in many books, forums, blogs, etc is what your camera does when you shoot a scene in the snow. Your camera will try to make all exposures average as much as possible giving a scene that results in your snow appearing gray since it is trying to balance the histogram (and trying not to blow anything out). You won't like the results, and that is because the reality is that you need the histogram to be shifted to the right, so all your snow appears white. My own experience with this problem came about while in Utah last summer at the Bonneville Salt Flats. I had a heck of a time trying to get a good exposure because I had to over-compensate for the exposure much more than I had ever done before... I think I had the exposure compensation set to +2 or more to get a good looking shot, and this histogram was not pretty to look at, but as others have said, a histogram is just a guide and is really most helpful when you know something is wrong, so that you can see how you might correct it. If the image looks right, the histogram shouldn't even matter.
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