Saturday, October 20, 2007

Lighting Fire Scenes for Digital Cameras

Yesterday I was in Beverly Hills doing a fire scene with an experienced fire investigator. It was a house where a fire started below the ground floor. The fireman tore up the floor in various rooms and removed sheetrock as usual and dumped it outside.

The scene was a confusion of possible causes. The house had workman in it doing staining of the kitchen cabinets, there was a mass of electrical wires at the area of origin, and after seeing the fire department photos BEFORE it was overhauled we had some very nice inverted-V pattern suggesting liquid flammables.

In any case, it was the usual mess of trying to take pictures in a deep space with a flash. A flash's light falls over with the square of the distance from the flash. This means that doubling the distance decreased the light power to 1/4. Dark deep spaces look like caves in the images.

The thing to do is to turn off the flash. Preferrably lean the camera, brace it, against some wall or door frame or,k even better, use a tripod. The exposure takes longer to happen, but the results are considerably better.

I intend to do a study on this for fire scenes to give some quick rules of thumb to make it easier for insurance adjustors, fire investigators, expert witnesses and forensic engineers to get some good images. Also the trade offs in various lighting techniques.

Derek Geer
Forensic Engineer
San Diego, California`

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Monday, October 1, 2007

Digital Photography: What's a pixel?

Forensic Engineers, Fire Investigators and Insurance Adjustors have all converted to digital photography. But what the heck is a pixel?

A pixel is a "picture element"! That's all.
Why is a pixel? Because digital electronics can only understand individual pieces of information. It constructs an image using really small pieces (pixels), which usually look like little squares on your computer screen if you can zoom in really close.
Camera resolution means how many pieces is the camera using. The more pieces, the more detail.
So, is more pixels always better? No! Why? Because there are good pixels and bad pixels. Bad pxels are those that don't show that part of the picture very accurately. So, it is better to have accurate pixels (once you have about 2 megapixels) than it is to have more pixels that are not accurate.
I will be posting some examples to make this clearer!

Derek Geer
Forensic Engineer
San Diego, California

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