Photog Chris's Blog

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Expose to the right

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Have you have ever used or looked at the histogram on your camera? All dSLR have them and many Point and Shoots do too. (If you have a Canon bring up the Live view to see it in action or with a taken picture just hit the display button till it shows up). The Histogram is useful in that it with a quick glance you can tell if you have a good exposure. Lets take a look at one.

A Histogram

I can tell that this one is pretty good but has some clipping in the high lights. The clipping doesn’t look too bad and can be adjusted if you are shooting in RAW.  It also tells me that most of the image data is in the bright part of the picture, and that is good. That means less noise.

You may notice that the histogram is broken up into 5 parts. Yes they run from dark to bright, but guess what? They are not equal. They look it but this is not a linear scale. The first section has 512 values, 1024 in the second, then 2048, 4096 and finally 8192 in the last. So the brightest part has 16 times more information then the darkest. This is just how things work, I can’t explain the reason behind it.

Still, we can make use of this info. With more data there is less noise. You can take a bright part and darken it without adding noise, but brightening a dark part will add noise.

Lets look at an example. Here are 5 pictures taken at 5 different exposures. What did I do? I set my camera to Manual, ISO to 100, Aperture to f4.0 and exposure mode to Evaluative (Matrix for you Nikon Guys). Then I adjusted my shutter speed till it showed +2 on the exposure bar. After which I adjusted the shutter to +1,0,-1 and -2 EVs.

+2 to -2 EVs

Then when importing with Adobe Camera Raw I adjusted the exposures accordingly to make them fairly even.

Each adjusted

The -2EV turned out a bit bright but they are all pretty close. Shrunk down to this size they all look pretty good. The two I had to brighten look like they lost some contrast but again, at this size they all look pretty close. So, lets look at some 100% Crops.

+2 EVs, adjusted down

+1 EV, adjusted down

0 EV, not adjusted

-1 EV, adjusted up

-2 EVs, adjusted up

Which one looks best to you? I personally like +1EV a little better then the 0 EV. Okay, maybe I would not shoot at +1 EV, more like +2/3 EV. The +2 EV definitely has blown high lights. The -1 and -2 EVs add quite a bit of noise. So yeah, it is down to +1 and 0. Lets take a look at their histograms.

Histogram for 0 EV

Histogram for +1 EV

Notice that 0 EV has a lot of data in the dark area, the noisy side of the graph. Look back up at the 100% crop and you’ll notice some noise in the green to the right. It is not too big a deal but if you wanted to brighten the shadows it might become one.

The +1 Ev show at peak at the far right, this shots clipping of the high lights. That is not too bad. Like I said, I would take it down a 1/3 stop to +2/3 EVs.

You want to see bad clipping? Here is the histogram for the +2 EV

+2 EV histogram

Okay, that’s about it.

Shoot in RAW. Check your histogram while shooting to see most of the data is to the right. Look for a spike at the far right, this is clipping and you don’t want that.  Adjust your exposure when importing.

Something not clear? I have other stuff on : Aperture, ISO, Shutter Speed.

Where do I learn this stuff?

A great page on Dynamic Range, A good discussion on 14bit sensors, and Luminous Landscape for a boat load of good stuff.

Any Questions or Corrections? Just let me know.

Chris

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Written by photogchris

June 15, 2010 at 6:11 pm

One Response

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  1. […] Look to the right of the page and you’ll see Expose to the Right. A new tutorial using this picture. Well, not exactly this picture. I did modify it quite a bit. Go […]


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