color2

So how do we insure that the images on the screen look like the original? The answer is we don't and can't. If your monitor had a week blue gun, then all images displayed on your CRT would have a yellow tint. We can only balance and make the image look very close to the original if the original is held near the screen, and the screen image is corrected until the two look alike. It is possible to add an object with known color reference to every shot. (not real practical, but possible.) If you adjust your monitor, making the known object correct, then the remaining information (other items on the screen) will probably be correct too.

The following demonstrates two methods that have been used to color correct the gemstone and mineral images at this site. Neither method is really correct, but both are useful in illustrating some of the pitfalls.

The lighting used to capture all of the images was derived from two halogen desk lamps and a tungsten spot light (see the previous section on camera and microscopes for more info). The color temperature of this combination is in the orange-yellow end of the spectrum.

Photo 1.

Histogram 1

Photo 2

The images were captured using the video camera connected to a Macintosh 8100 AV computer. Images were captured using the Apple supplied Video Capture software, and then COPY and PASTEd into Adobe Photoshop. Photoshop was then used to modify the original images in a variety of ways.

Photo 1. represents the image captured by the system before ANY modifications, and Histogram 1 is that displayed in the Levels... selection within Photoshop. (Created from the Image Menu and Adjust Levels command.) To my eye the image was strongly over balanced in the magenta/red direction. (Compared to the original.)

I first used the Photoshop lasso tool (Photo 2.) and outlined the gemstone, separating it from the background. By using the Inverse command from the Select menu, I can select to work on either the background (red arrows) or the gemstone (blue arrows). I usually work on the background first. I select the background and then go again to the Image menu and select... Adjust Variations.

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