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by Bart Arondson

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Many times I shot photos, but the photo is some times too bright or too dark and the colors are incorrect.

Some times the white on the photo is not the white that I have on background but gray and I see that not on camera, but when I input the image on the computer. I can not match the white background on the pages.

How can correctly meter light with proper color balance? Are there any tips, tricks, books, or web sites?

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WB and metering are really mixed up in this question. :( –  mattdm Mar 24 '11 at 3:34

3 Answers 3

up vote 14 down vote accepted

The problem is that the exposure meter in the camera does not know whether the subject itself is bright or not. It simply measures the amount of light that comes in, and makes a guess based on that. The camera will aim for 18% gray, meaning if you take a photo of an entirely white surface, and an entirely black surface you should get two identical images which both are gray (at least in theory). This means that if your scene is very bright you will need to over-expose the image. Otherwise the camera's exposure meter will be fooled, and produce an image that is too dark. The opposite goes for a dark scene, here you will need to under-expose.

When I have a subject that contains a white surface that I really want to be white, I often spot-meter on that surface, and then set an exposure in the camera that is around 1.5 to 2 steps brighter than that (so if spot-metering on the white suggests an exposure time of 1/250, I will instead use something around 1/90 - 1/60).

Also, the histogram is a good tool for this. If you have bright parts of your scene, you want the histogram to reach as close to the right edge as possible, preferably without blowing out any highlights. The Expose Right article on Lumonous Landscape offers some good info on that.

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+1 Excellent answer. Very clearly explained. –  jrista Aug 9 '10 at 2:20
    
If you compensate 1/60 to 1/160-1/250 you're actually underexposing, aren't you? –  Karel Aug 9 '10 at 22:01
    
@Karel: you are absolutely correct. I can't believe that I missed that. Will fix immediately. –  Fredrik Mörk Aug 10 '10 at 6:36

That's a huge question. I'm going to assume you're a beginner, because of the lack of jargon in the question -- apologies if I'm wrong about that...

Anyway: there are plenty of resources to learn about exposure -- I'd recommend the book "Understanding Exposure", but I'm sure you'll get plenty of suggestions to choose from.

[EDIT: added the next two paras because I felt guilty about just saying "read this book!" and nothing else]

For a quick fix, you could try using exposure compensation. This lets you tell the camera to make the picture darker or lighter; it's normally indicated by a scale that goes from EV -2 (darker) to EV +2 (lighter). Your camera manual will tell you how to use this; if you're in automatic mode, you'll probably have to switch to program auto first.

For a real fix, you have to understand why your camera is making the scene too bright or too dark. If you're in automatic mode, that will be down to metering. Most cameras will give you a choice between measuring the amount of light at a single point ("spot metering"), or averaging over the whole frame, or some more complicated option. Have a look at the metering options in your camera's manual, and experiment with them -- try taking a few pictures of a scene that contains both very bright and very dark areas.

The problem of colours not being correct might be to do with the white balance on your camera (if there's an overall colour cast - say, everything looks blueish, or yellowish), but that's just a guess.

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"Understanding exposure" is a very valuable book ! I totally aggre with @Matt –  Jean-Philippe Caruana Jul 21 '10 at 10:26
    
what means "lack of jargon" ? :) –  Aristos Jul 23 '10 at 5:36
    
You're asking a question about metering, exposure, and white balance - but without using any of those words. To me, that suggests either "beginner", or "native language isn't English", or both... (apologies, again, if I guessed wrong!) –  Matt Bishop Jul 23 '10 at 8:05

There seems to be two things here; getting the correct exposure, and getting the correct white balance. What sort of camera are you using? I'm going to answer as if it were a D-SLR, but if it's not I'll edit this post according to your response.

For the former, the key thing to remember is that your camera only has a finite dynamic range (that is if you have a subject that is both very bright and very dark in places, one or the other will most probably lose detail due to highlights being blown or the darks all being too dark). You'll want to use the metering mode on your camera to get the exposure you want correct for the part of the photo you are interested in. If you have a bright subject against a dark background, I'd probably use spot-metering on the subject to get the subject exposed correctly, and let the background be dark. If my subject was bright against a medium-bright background I would probably choose to use centre-weighted metering to try and get a good compromise between the exposures ideally required to capture the foreground and background correctly. For things such as silhouettes I'd probably spot-meter on the background, meaning the darker foreground was black.

To fix the second problem you describe, namely the colours and particuarly whites, being off, then you probably need to adjust the white balance. Your camera will probably have an auto-wb setting, which you could use, or you could set it based on the lighting conditions whenever you take a photo. Another option is to photograph a greycard, and have the camera use a custom white balance. Personally, I shoot in RAW and then adjust the white balance in Lightroom if necessary.

It could also be a problem of colour management. Syl Arena's written an article about it, but essentially you need to ensure that your camera records colour in the same way that your monitor displays colour and your printer prints colour. You do this by profiling the various devices.

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Very pertinent point about checking the monitor etc. It's something that we may take for granted, but I'm yet to come across a display that isn't noticeably wrong when measured with a colorimeter. –  Rowland Shaw Jul 21 '10 at 20:21

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