 NAVNITH KRISHNAN |
The Histogram: What It Is, How It's Used I am a bit confused by the histogram. Can somebody explain to me how to read histogram and how one can use it to improve photography? I have a Nikon D70s.
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doug Nelson |
A histogram divides the available tones of light and dark in an image into 256 shades. It shows the distribution of shades in the overall image. It is important to know that a histogram shows you nothing about where in the image the tones happen to be, just how many of each shade is there, relative to the other shades. So, for a practical example, all of the histogram bunched up on the left tells you the image is a preponderance of dark tones. Bunched up on the right is a high-key image, with mostly bright tones. An even distribution tells you that there are about as many brights as darks. A histogram will also show you where there is no tonal information, usually at the extreme ends of the scale. Imaging operators usually will move the slider on each end over to just the point at which tonal information is being shown. Most images, whether out of a digital camera, or from a scanner, look a lot better when you do this. Editor's Note: For anyone interested, BetterPhoto offers this June online course:
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doug Nelson |
One more tip, the histogram with the adjustable sliders will be found in Levels, under Image/Adjust, depending on which version of Photoshop or Elements you have. See www.cambridgeincolour.com for some nice tutorials on this subject.
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Slim Brady |
A light meter reading tells you what exposure will render a standard 18% gray reference card as a mid tone. This reading may have been made because the camera read a variety of areas of the scene and averaged them out, or because you read the highlights, the shadows and some other areas and decided that a particular setting would yield the best compromise exposure for that scene. This setting, like every other that you or your automated camera makes, is a compromise. In most real world situations there is no such thing as an ideal or “perfect” exposure. There is simply one that places the tonal values found in the scene most appropriately within the capability range of the camera’s imaging chip. And "most appropriately" means that the mid-tones found in the image fall roughly half way between the darkest and the brightest values.
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Sabrina Dionne |
Peaks and valleys bunched against the left the image is probably underexposed. And bunched to the right, overexposed. Then again: Most shots you take, the peaks and valleys should be in the middle with a little more to the right. keep in mind however there is no "perfect" histogram.(See picture)Here the highlights are OK. Losing a bit of the dynamic range in the highlight area but a good photo editing program can correct for this. Good reading:http://www.sphoto.com/techinfo/histograms/histograms.htm , American Photo Magazine, March/April issue. Site to visit: http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml or take an online course through betterphoto.com http://www.betterphoto.com/photocourses/ELL02.php . Hope this helps,
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Sabrina Dionne |
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Christopher A. Vedros |
While we're on the subject . . . I've read a couple articles about the merits of Exposing To The Right of the histogram. This method (ETTR for short) is based on the idea that most of the tonal information in any image is contained in the brightest tones. I'd love to hear comments from some other photographers who have tried this method. I've tried it, and have had better results doing just the opposite, or intentionally UNDERexposing my images just a little. I have 2 problems with the ETTR method: I'd like to hear what other people think. Chris A. Vedros
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Zj >>> ZJ Images |
Navnith... I agree with the responses I've read to your question about histograms. However, let me add that the Nikon D70 reads only the green channel of the exposure NOT all three RGB channels like some higher end D-slrs. Generally this doesn't pose a significant problem unless there's a predominace of red in your shot (red fall leaves, red barn, etc.). The D70 will indicate a correctly exposed histogram but in fact it will vastly overexpose the image and you won't know this until you view the shot after the fact. Keep this in mind and expose more to the left to correct. Regarding exposing to the right: I adopted this strategy over a year ago after making many tests. It works for me. And yes it is sometimes difficult to get the exposure right but it is worth it.
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David A. Bliss |
Chris, I shot slide film for a long time before I went digital. It was so ingrained in me to underexpose slightly that it was a hard habit to break when I started shooting digitally. On a digital picture, brightening underexposed areas will add more noise and color imperfections than darkening overexposed areas. If a highlight is blown, there is nothing that can be done, just like film. White is white, and darkening it will just turn it gray. But if it still has detail, then you can darken that area and still have detail, with less noise and fluctuation than the other way around. That is why it is considered better to slightly overexpose, or at least lean toward that direction. Obviously, it is better to have the exposure perfect from the get go. ;-)
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Ariel Lepor |
I've had over exposed photos that I corrected on the computer, but, even though it had all the details, it looked too artificial. I've also brightened underexposed pictures, and lowered noise levels, and it looks more natural, but with more noise than I'd like. I have no idea why anyone would try to take a bad picture and try make it perfect on the computer. You don't get any more detail in shots this way.
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Jerry Frazier |
This conversation could go all over the map. Much is a matter of preference. I like to blow out sometimes. It just doesn't bother me at all, and at times, has become somewhat stylized these days. But, it depends on what you are blowing out, and why. And, the artisits intent is everything. Because, it IS about control. I like to underexpose a tad. Digital retains far more detail in the dark than it does in the highlights. But, you don't have to take my word for it, thanks to technology, it's easy to test for yourself. Take a photo of something and expose it properly, then over expose it about 1/2 or 1 stop, then under expose about 1/2 or 1 whole stop. Then take a look at the results. What I find is I can bring up more detail in the underexposed image. But, as someone mentioned, if you are shooting at high ISO's, it can introduce noise. But, I haven't really had a problem with this when shooting at ISO 250 or 400 or something. I only have had issue when shooting at ISO 1600 or 3200. Then, yes, noise is obvious. But, of course, unlike most, I don't mind noise, and often create it for effect. I used to do the same thing with film. Love grainy photos. Anyways, learning to read a histogram does take some time, but it's not all that hard. If you are photographing someone in strong backlight, the curve will be way off to the right, but if you look at the image, it will be OK. It's because it's seeing all that backlight dominating the image. But, if that's what your intention is, then it's OK. It takes some practice and alot of trial and error.
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- Craig m. Zacarelli Contact Craig m. Zacarelli Craig m. Zacarelli's Gallery |
what about your metering mode? wouldnt you need to consider what the subject is your shotting and decied the proper metering mode to expose it correctly? I mean, I brightly back lit small subject for example, would you use spot or center weighted or evaluative? it depends on what your looking for doesnt it? I would tend to use spot but wouldnt that just "blow out" the bright BG? There are just sooo Many variables to consider... I was out on saturday and it was really sunny so I was using the ND grad and it really helped... I used to use it only for waterfalls and such but it helped, even in spots where there was allot of sun/shade... Craig-
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