Welcome to the MedLibrary.org Wikipedia Supplement on Colorimetric -- Please Click to Return to Front Page

Colorimetry or Colourimetry can refer to:

• the quantitative study of color perception.^[1] It is similar to spectrophotometry, but may be distinguished by its interest in reducing spectra to tristimulus values, from which the perception of color derives.
• the determination of the spectral absorbance of a solution.

Instruments

Colorimetric equipment is similar to that used in spectrophotometry. Some related equipment is also mentioned for completeness.

• A tristimulus colorimeter measures the tristimulus values of a color.^[2]
• A spectroradiometer measures the absolute spectral radiance (intensity) or irradiance of a light source.^[3]
• A spectrophotometer measures the spectral reflectance, transmittance, or relative irradiance of a color sample.^[3][4]
• A spectrocolorimeter is a spectrophotometer that can calculate tristimulus values.
• A densitometer measures the degree of light passing through or reflected by a subject.^[2]
• A color temperature meter measures the color temperature of an incident illuminant.

Two spectral reflectance curves. The object in question reflects light with shorter wavelengths while absorbing those in others, lending it a blue appearance.

Absorption colorimeter

In physical chemistry, a colorimeter is a device used to test the concentration of a solution by measuring its absorbance of a specific wavelength of light. To use this device, different solutions must be made, and a control (usually a mixture of distilled water and another solution) is first filled into a cuvette and placed inside a colorimeter to calibrate the machine. Only after the device has been calibrated can you use it to find the densities and/or concentrations of the other solutions. You do this by repeating the calibration, except with cuvettes filled with the other solutions. The filter on a colorimeter must be set to red if the liquid is blue. The size of the filter initially chosen for the colorimeter is extremely important, as the wavelength of light that is transmitted by the colorimeter has to be same as that absorbed by the substance.

Tristimulus colorimeter

In digital imaging, colorimeters are tristimulus devices used for color calibration. Accurate color profiles ensure consistency throughout the imaging workflow, from acquisition to output.

Spectroradiometer, Spectrophotometer, Spectrocolorimeter

The absolute spectral power distribution of a light source can be measured with a spectroradiometer, which works by optically collecting the light, then passing it through a monochromator before reading it in narrow bands of wavelength.

Reflected color can be measured using a spectrophotometer (also called spectroreflectometer or reflectometer), which takes measurements in the visible region (and a little beyond) of a given color sample. If the custom of taking readings at 10 nanometer increments is followed, the visible light range of 400-700nm will yield 31 readings. These readings are typically used to draw the sample's spectral reflectance curve (how much it reflects, as a function of wavelength); the most accurate data that can be provided regarding its characteristics.

CRT phosphors

The readings by themselves are typically not as useful as their tristimulus values, which can be converted into chromaticity co-ordinates and manipulated through color space transformations. For this purpose, a spectrocolorimeter may be used. A spectrocolorimeter is simply a spectrophotometer that can estimate tristimulus values by numerical integration (of the color matching functions' inner product with the illuminant's spectral power distribution).^[4] One benefit of spectrocolorimeters over tristimulus colorimeters is that they do not have optical filters, which are subject to manufacturing variance, and have a fixed spectral transmittance curve—until they age.^[5] On the other hand, tristimulus colorimeters are purpose-built, cheaper, and easier to use.^[6]

The CIE recommends using measurement intervals under 5nm, even for smooth spectra.^[3] Sparser measurements fail to accurately characterize spiky emission spectra, such as that of the red phosphor of a CRT display, depicted aside.

Color temperature meter

Photographers and cinematographers use information provided by these meters to decide what color correction should be done to make different light sources appear to have the same color temperature. If the user enters the reference color temperature, the meter can calculate the mired difference between the measurement and the reference, enabling the user to choose a corrective color gel or photographic filter with the closest mired factor.^[7]

The normals are lines of equal correlated color temperature.

Internally the meter is typically a silicon photodiode tristimulus colorimeter.^[7] The correlated color temperature can be calculated from the tristimulus values by first calculating the chromaticity co-ordinates in the CIE 1960 color space, then finding the closest point on the Planckian locus.

See also

• Photometry
• Radiometry

References

1. ^ Ohno, Yoshi (Oct. 16-20 2000). "CIE Fundamentals for Color Measurements" in IS&T NIP16 Conference. Vancouver, Canada: 540-545. 
2. ^ ^{a b} ICC White Paper #5
3. ^ ^{a b c} Lee, Hsien-Che (2005). "15.1: Spectral Measurements", Introduction to Color Imaging Science. Cambridge University Press, 369–374. ISBN 052184388X. "The process recommended by the CIE for computing the tristimulus values is to use 1 nm interval or 5 nm interval if the spectral function is smooth" 
4. ^ ^{a b} Schanda, János (2007). "Tristimulus Color Measurement of Self-Luminous Sources", Colorimetry: Understanding the CIE System. Wiley Interscience. doi:10.1002/9780470175637.ch6. ISBN 978-0-470-04904-4. 
5. ^ Andreas Brant, GretagMacbeth Corporate Support (2005-01-07). "Colorimeter vs. Spectro". Colorsync-users Digest. Retrieved on 2008-05-06.
6. ^ Raymond Cheydleur, X-Rite (2005-01-08). "Colorimeter vs. Spectro". Colorsync-users Digest. Retrieved on 2008-05-06.
7. ^ ^{a b} Salvaggio, Carl (2007). in Michael R. Peres: The Focal Encyclopedia of Photography: Digital Imaging, Theory and Application, 4E, Focal Press, pg.741. ISBN 0240807405. 

Further reading

• Schanda, János D. (1997). "Colorimetry", in Casimer DeCusatis: Handbook of Applied Photometry. OSA/AIP, 327–412. ISBN 978-1563964169. 
• Bala, Raja (2003). "Device Characterization", in Gaurav Sharma: Digital Color Imaging Handbook. CRC Press. ISBN 9780849309007. 
• Gardner, James L. (May-June 2007). "Comparison of Calibration Methods for Tristimulus Colorimeters". Journal of Research of the National Institute of Standards and Technology 112 (3): 129–138. 

External links

• MacEvoy, Bruce (2008-05-08). "Overview of the development and applications of colorimetry". Handprint.com. Retrieved on 2008-07-17.
• Colorimetric equipment by X-Rite Optronik An informative brochure with background information and specifications of their equipment.

Wikipedia content modification information:

• This page was last modified on 30 September 2008, at 02:15.

Wikipedia Authorship and Review

Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.

Wikipedia Usage Guidelines

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Colorimetric".

The URL for this specific entry is:

• http://medlibrary.org/medwiki/Colorimetric

All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.