Method, system and apparatus for jointly calibrating color digital cameras and monitors

1. A method for calibrating and characterizing a color display, the method comprising:

operating a light source including a plurality of light emitters to emit light, including:

selecting light emitters in the light source determined as producing a largest signal for each of the RG and B channels of a color capture device; and

generating a plurality of intensity steps by operating each selected light emitter at a plurality of intensities ranging from zero power to full power; and

calibrating and characterizing the color capture device based on the emitted light, including:

capturing each of the plurality of intensity steps by the color capture device;

computing transforms relating intensity-proportional RGB channel values to camera RGB channel counts based on known luminances for the selected light emitters;

collecting a plurality of images from the color capture device, each collected image corresponding to one of the selected light emitters in the light source being operated;

computing image statistics for each collected image;

converting capture device RGB values for each collected image to linearized R′G′B′ values based on the computed transforms; and

computing color capture device spectral responsivities from known spectral power distributions of the light emitters and the linearized R′G′B′ values;

displaying color images on the color display;

capturing the displayed color images on the color capture device; and

calibrating and characterizing the color display based on the captured color images.

2. The method set forth in claim 1 , wherein:

the step of operating a light source to emit light includes mixing the emitted light to produce a composite stimulus.

3. The method set forth in claim 1 , wherein the color capture device comprises a digital camera.

4. The method set forth in claim 1 , wherein the color capture device comprises a digital video camera.

5. The method set forth in claim 1 , the step of characterizing the color capture device further including:

computing color management profiles for the color capture device based on the computed color capture device spectral responsivities and the computed transforms.

6. The method set forth in claim 1 , wherein:

the step of displaying color images on the color display includes:

displaying a white patch at a maximum white value of the color display; and

adjusting a shutter speed and aperture setting of the color capture device to obtain white point RGB values slightly less than a saturation level of the color capture device; and

the step of calibrating and characterizing the color display includes:

displaying a plurality of color patches representing a sampling of a color gamut of the color capture device including gamut boundary colors;

computing colorimetric specifications of each displayed color patch based on results of the step of calibrating and characterizing the color capture device; and

computing a model relating display RGB values to CIE XYZ values based on the white point RGB values and the computed colorimetric specifications.

7. The method set forth in claim 6 , wherein:

the step of displaying a white patch at a maximum white value includes setting the color capture device to an automatic white balance mode.

8. The method set forth in claim 6 , wherein:

the step of displaying color images on the color display further includes:

displaying an alignment target image on the color display; and

positioning the color capture device in front of the color display with the alignment target image centered in the color capture device image.

9. A computer program product for calibrating and characterizing a color display comprising:

a non-transitory computer readable medium;

computer program instructions, recorded on the computer readable medium, executable by a processor, for performing the steps of:

operating a light source including a plurality of light emitters to emit light,

determining light emitters in the light source producing a largest signal for each of the RG and B channels of a color capture device; and

generating a plurality of intensity steps by operating each selected light emitter at a plurality of intensities ranging from zero power to full power; and

calibrating and characterizing the color capture device based on the emitted light, including:

capturing each of the plurality of intensity steps by the color capture device;

computing transforms relating intensity-proportional RGB channel values to camera RGB channel counts based on known luminances for the selected light emitters;

collecting a plurality of images from the color capture device, each collected image corresponding to one of the selected light emitters in the light source being operated;

computing image statistics for each collected image;

converting capture device RGB values for each collected image to linearized R′G′B′ values based on the computed transforms; and

computing color capture device spectral responsivities from known spectral power distributions of the light emitters and the linearized R′G′B′ values; and

displaying color images on the color display;

capturing the displayed color images on the color capture device; and

calibrating and characterizing the color display based on the captured color images.

10. The computer program product set forth in claim 9 , further comprising:

a computer system for receiving user inputs, wherein the computer system houses the processor and is operatively connected to the light source for controlling operation of the plurality of light emitters, and operatively connected to the color display for controlling operation of the color display; and

a lens or diffuser system for focusing or mixing the emitted light from the light source to produce a composite stimulus.

11. The computer program product set forth in claim 9 , wherein the plurality of light emitters comprise a plurality of LEDs, and wherein the color capture device comprises at least one of a digital camera and a digital video camera.

12. The computer program product set forth in claim 9 , wherein:

the step of operating the light source includes:

selecting three light emitters in the light source and individually illuminating each one of the three light emitters; and

the step of displaying color images on the color display includes:

displaying a white patch at a maximum white value of the color display; and

adjusting a shutter speed and aperture setting of the color capture device to obtain white point RGB values slightly less than a saturation level of the color capture device; and

the step of calibrating and characterizing the color display includes:

displaying a plurality of color patches representing a sampling of a color gamut of the color capture device including gamut boundary colors;

computing colorimetric specifications of each displayed color patch based on results of the step of calibrating and characterizing the color display; and

computing a model relating display RGB values to CIE XYZ values based on the white point RGB values and the computed colorimetric specifications.

13. The computer program product set forth in claim 12 , wherein:

the step of characterizing the color capture device further includes:

computing color management profiles for the color capture device based on the computed color capture device spectral responsivities and the computed transforms;

the step of displaying a white patch at a maximum white value includes setting the color display to an automatic white balance mode; and

the step of displaying color images on the color display further includes:

displaying an alignment target image on the color display; and

positioning the color capture device in front of the color display with the alignment target image centered in the color capture device image.