Message
Re: [colorvision_group] spectrocolorimeter usage
2008-04-25 by CDTobie@aol.com
In a message dated 4/25/08 2:53:50 PM, kenchow@... writes:
Is it possible to use the spectrocolorimeter to directly measure color
values from an original art work (watercolor, oil, acrylic) and relate
them to a digital capture of that piece for the purposes of color matching?
Yes, though accuracy of this type of device (called a 0/45 device as it views at zero degrees, and illuminates at 45 degrees) is highest for flat surfaces, and less exacting for textured surfaces, or heavy clearcoats over the colors.
For example can RGB values from the original be measured or derived -
then I can compare that to the RGB values of that section of the digital
capture and determine how far off it is...
Lab values are real world values, and contain factors not included in RGB values. But a file with a reasonable "RGB to Lab relationship" (meaning a file in a Photoshop RGB workingspace such as AdobeRGB) would be capable of reasonably matching colors, within the colorspace. Its a tricky business, since the "image" on screen also includes the illuminant it was photographed under, and values in textured images contain sheen and shadow factors.
The easiest method would be to use the Lab values from the spot measurements, and set the Photoshop info tool to read in both your RGB space, and in Lab.
I see from the documentation that Lab values can be measured, does that
accomplish the same thing in some way?
Whether you can achieve what you are attempting depends on a number of complicating factors, but its certainly worth attempting. Using high quality 5000k lighting when shooting the painting would be helpful, and avoiding huge workingspaces such as ProPhotoRGB would assist as well.
C. David Tobie
WW Product Technology Manager
Digital Imaging & Home Theater
Datacolor
CDTobie@...
www.datacolor.com/Spyder3
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