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Auto White Balance

February 10, 2011

I have been using a Canon PowerShot A70 for years.  Obviously there are better cameras now, but this one has served me well, and Canon recently replaced the ccd for free.

http://www.usa.canon.com/cusa/support/consumer/digital_cameras/

powershot_a_series/powershot_a70#Specifications

For class this week, Eric Rosenthal asked us to take a picture without the auto white balance, setting it manually with a gray card.  I took three pictures: the first set to Auto as a control, and the other two set to P–in this mode the camera still controls shutter speed and aperture, but I can control the white balance and light metering method.  White balance is set by filling the frame with the gray card at the location of average light in the picture, and then pressing “Set”.  As for the light metering method, there are three settings: Evaluative, Center-Weighted and Spot AE Point.  In the first “P” picture, I used Evaluative metering, and the second, Spot.

Auto:

P: Evaluative Metering:


P: Spot Metering on Gray Card:

Auto:

P: Evaluative Metering:

P: Spot Metering on Gray Card:

The Auto setting definitely gives a blue cast to the whites.  The Evaluative and Spot metering is not tremendously different in these two cases, but there’s a bit more yellow in the the Evaluative whites, and a broader range with less lost detail in the shadows with Spot metering.

I guess the whites are a little blown out though.  Eric comments: “Looks like the color is corrected in the evaluative metering images.  The spot metering images are both over exposed.  You probably used a location in the image that was too dark so the exposer got set wrong.  Are you convinced yet that the grey card improves the color.”

I’ve always thought this camera takes pretty great pictures right out of the box (Auto settings), but I’m impressed by how blue the light actually is, and how much the gray card does help with color balance.  The next experiment will be to compare the camera’s auto white balance settings.

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