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Step 2Using Your Reference
There are two distinctly different ways to use the color reference. The first method works only for digital cameras that allow you to set a manual color balance by sampling a scene:
As shown in the figure, simply hold the neutral gray reference in the lighting that is hitting your subjects and sample it to set the "manual white balance." That's it. Jpeg images straight from the camera should be reasonably well balanced until/unless the lighting changes. Of course, don't forget to change the white balance when you use the camera in different lighting (some cameras retain manual white settings across being turned off and on again). Incidentally, you can also use this method to digitally apply any color filter you wish -- simply use a gray card that is tinted the opposite color (e.g., blue tint reference to produce orange filter effect).
The second technique works with any type of camera (even film) and is potentially much more precise, but is more complex and requires post-processing of the images:
If you are using a digital camera, set the white balance to "daylight" (or whichever fixed setting seems closest to correct in the current lighting -- but not "auto") or shoot in "raw" mode. Raw images usually are not affected by the white balance settings in the camera and can yield higher image quality. For a film camera, stick to the same film type, chemical processing, and scanning process.
1. Take a separate photograph of the reference -- possibly out of focus, but filling most of the frame.
2. Shoot as many photos as you like under the same lighting conditions used for the reference.
3. Once you've downloaded the images to your computer, use your favorite image editing program (e.g., photoshop, gimp, cinepaint) to tweak the color balance so that the reference image colors closely match the color values you know they should have. Keep in mind that the RGB values don't have to match, because the reference colors can be slightly under or over exposed. In a color space like LAB or YUV, the L (lightness) or Y (luma, brightness) component might not match.
4. That same set of adjustments is then applied to correct all the photos you shot under the same lighting conditions.
If you made your own color reference, you might not know precisely what the digital values of your reference colors should be for step 3. If so, you can get a usable approximation by taking a photo of them under nice, standard, "daylight" conditions and matching to that. Most cameras and films deliver pretty accurate (or at least pleasing) colors under standard daylight conditions.
As shown in the figure, simply hold the neutral gray reference in the lighting that is hitting your subjects and sample it to set the "manual white balance." That's it. Jpeg images straight from the camera should be reasonably well balanced until/unless the lighting changes. Of course, don't forget to change the white balance when you use the camera in different lighting (some cameras retain manual white settings across being turned off and on again). Incidentally, you can also use this method to digitally apply any color filter you wish -- simply use a gray card that is tinted the opposite color (e.g., blue tint reference to produce orange filter effect).
The second technique works with any type of camera (even film) and is potentially much more precise, but is more complex and requires post-processing of the images:
If you are using a digital camera, set the white balance to "daylight" (or whichever fixed setting seems closest to correct in the current lighting -- but not "auto") or shoot in "raw" mode. Raw images usually are not affected by the white balance settings in the camera and can yield higher image quality. For a film camera, stick to the same film type, chemical processing, and scanning process.
1. Take a separate photograph of the reference -- possibly out of focus, but filling most of the frame.
2. Shoot as many photos as you like under the same lighting conditions used for the reference.
3. Once you've downloaded the images to your computer, use your favorite image editing program (e.g., photoshop, gimp, cinepaint) to tweak the color balance so that the reference image colors closely match the color values you know they should have. Keep in mind that the RGB values don't have to match, because the reference colors can be slightly under or over exposed. In a color space like LAB or YUV, the L (lightness) or Y (luma, brightness) component might not match.
4. That same set of adjustments is then applied to correct all the photos you shot under the same lighting conditions.
If you made your own color reference, you might not know precisely what the digital values of your reference colors should be for step 3. If so, you can get a usable approximation by taking a photo of them under nice, standard, "daylight" conditions and matching to that. Most cameras and films deliver pretty accurate (or at least pleasing) colors under standard daylight conditions.
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