Re: Colorimetric Accuracy in the Field
Re: Colorimetric Accuracy in the Field
- Subject: Re: Colorimetric Accuracy in the Field
- From: Robin Myers <email@hidden>
- Date: Mon, 03 Jun 2013 19:03:46 -0700
On Jun 3, 2013, at 6:13 PM, Don Schaefer wrote:
> <snipped>
>
> Therefore, the question came up before and I would like to ask again, how
> do I do an adequate color balance at "sunset with the model at the beach
> during magic hour"? The Passport? Then what?
Set up your camera and a color chart holder, an artist's easel works well, outdoors in the summer at noon. Illuminate the easel at 45 degrees to where the chart's surface will be. This means having the sun to your left or right. The camera is positioned perpendicularly to the center of the chart. Put the chart on the easel (I use a dummy piece of cardboard until everything is ready to reduce UV exposure of my chart) and expose the chart properly. By this I mean that the white patch in the center of the ColorChecker SG is as close to 245 in the green channel as possible (slight under-exposure is better than overexposure). Make sure that the area around the chart is a matte black material (this is to reduce veiling glare), and also use a lens hood.
To improve your profile make sure you turn off as much of the camera processing as possible. This includes automatic exposure, contrast enhancement, sharpening, noise reduction, etcetera.
Once you have a properly exposed chart image (exposed to the white number given above), adjust the image for the lens fall-off (the lighting should be even or there is something seriously wrong), then neutral balance your image using a mid-tone gray. I suggest using one, or all, of the patches G5, G6, H5, H6. Do not use any of the white, light, or dark gray patches for neutral balancing.
Make your profile with your favorite tool.
Now you have a profile to produce the equivalent of daylight film. When you are shooting late or early in the day use this profile and you will keep the golden colors. Do not make a profile for the early morning or late afternoon light, you will not like the results.
If you are using a ColorChecker Classic (either the Classic itself or the ColorChecker Passport version), the white is exposed to produce as close to 243 as possible and use the N6.5 or N5 patches for the neutral balance.
Robin Myers
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