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June 25, 2008

[WHITER THAN WHITE]

 

TODAY WE TACKLE A SERIOUS DIGITAL PHOTOGRAPHY ISSUE – why do the entire family look as though they are suffering from terrible jaundice in the Christmas photos? Here they are, sitting around the groaning festive board, funny hats askew and the pudding on fire and their faces are beyond ruddy. They are yellow, tending to orange.

But then, in the photos taken later in the afternoon of Uncle Cyril snoozing on the back veranda, he looks like a hypothermia victim. What is going on?

Well, it’s called white balance. Or colour temperature. And digital cameras, left to their own devices, are not as good at detecting and correcting colour temperature shifts as our eyes are. We don’t notice the orange cast from tungsten light and we automatically correct for the blue cast in shadows.

All digital cameras, straight from the box, are set to automatically correct white balance, but it doesn’t always work well. For this reason cameras have manually selected white balance settings from which the user can choose. Choosing the tungsten or shade setting will usually give a better colour accuracy in those situations. But better yet is to set the white balance manually.

This is impractical for spontaneous photography, but what we are considering here is the situation where time and the immobility of the subject are on your side. We ran some tests using different techniques and gadgets for setting the colour temperature, using a still life setup lit with sunlight through a window and two halogen flood lights with a decidedly yellow bias.

First we let the camera decide, using the Auto white balance. The result was awful. The yellow cast was dark and dirty and very difficult to correct in Photoshop.

Next we used white balance bracketing in the camera. This method involves taking one shot and letting the camera generate three saved images – one corrected to magenta on the magenta/amber axis, one corrected towards amber and the third at what the camera reckons is correct. The results were poor. There were not enough variations along the m/a axis.

Then we tried a nine set bracket, which can only be done in a few cameras, and the Nikon D300 is one of them. From nine variations we found one that was acceptable.

Then we turned to manually setting the white balance. First we used a White Balance Lens cap, which is a disc of translucent white plastic. On the camera white balance selection scale you select Preset or Manual and, following the instructions in the camera manual, you point the camera at the lit subject and take a non-photo which is used for calibration. We bought our lens caps for three different lenses from Hong Kong for a few dollars each.

Results with the lens cap method were good, with a slight tendency to blue. It was the best result so far, but not perfect.

Then we used a Lastolite flexible “card”, printed 18 per cent grey on one side and white on the other (about $28) to preset white balance. Using the grey side as the target we got the best results. The image using the grey card (simple ones can be bought for as little as $3) needed no post camera colour correction.

We recommend the lens cap for convenience and the grey card for accuracy.

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Posted by terry at June 25, 2008 11:54 PM

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Posted by: Tony M at June 27, 2008 01:10 PM

Posted by: Dale at June 28, 2008 05:04 AM

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