Trichromatic Image Research Articles

A Comparative Analysis of Spectral Reflectance Estimated in Various Spaces Using a Trichromatic Camera System

Principal component analysis coupled with multi-channel digital image capture is a powerful technique for spectral scene estimation. Most often, the linear modeling is performed using a spectral reflectance factor. However, it is well known that for many subtractive coloration systems, spectral reflectance is nonlinearly related to colorant amount. Accordingly, the accuracy of spectral reconstruction has been evaluated as a function of the spectral definition of the ensemble. Specifically, Kubelka-Munk turbid media theory and a new empirical transformation, optimized for optimal data normality, were compared with spectral reflectance factor. Both tested spaces are nonlinear transformations of spectral reflectance factor. In addition, a new technique of multi-channel digital image capture was developed and tested. This technique combined trichromatic image capture with color filtration resulting in multiple signals in sets of three. Six eigenvectors based on the new empirical space coupled with digital capture with and without a light-blue absorption filter produced the most accurate spectral scene estimation from among the various tested combinations.

Photopigment transmittance imaging of the primate photoreceptor mosaic

We introduce a new technique for classifying many photoreceptors simultaneously in fresh, excised primate retina on the basis of their absorptance spectra. Primate retina is removed from the pigment epithelium and illuminated under a microscope from the same direction as in the intact eye. To facilitate the guiding of light into the receptor outer segments, the optical axes of the photoreceptors are oriented parallel to the optical axis of the microscope. Photoreceptor outer-segment tips are imaged on a charge-coupled device array, which provides radiometric measurements of the light passing through each photoreceptor. These images are acquired sequentially at three wavelengths chosen to maximize the absorptance differences among the three cone photopigments. After the photopigment is bleached, a second set of three images is acquired. The ratios of the images before and after bleaching at each wavelength are photopigment transmittance maps of the retina. These are combined into a single trichromatic image showing the distribution of photopigment if the retina could be viewed directly in white light without bleaching. We have found patches of receptors in peripheral macaque retina where the measured absorptance at the wavelength of maximum absorptance is consistent with the predicted axial absorptance of th photopigment. The cones in these patches cluster into two groups corresponding to the middle wavelength-sensitive (n = 53, mean absorptance = 0.28) and the long wavelength-sensitive (n = 63, mean absorptance = 0.30) cones. The mean absorptances of 273 macaque and 183 human rods were 0.51 and 0.41, respectively.

Software for producing trichromatic images in astronomy

We present a software package for combining three monochromatic images of an astronomical object into a trichromatic color image. We first discuss the meaning of “true” colors in astronomical images. We then describe the different steps of our method, choosing the relevant dynamic intensity range in each filter, inventorying the different colors, optimizing the color map, modifying the balance of colors, and enhancing contrasts at low intensity levels. While the first steps are automatic, the last two are interactive.

Single bit-map block truncation coding of color images

A color-image data compression technique based on block truncation coding (BTC) is described. BTC is first implemented to encode a weighted trichromatic image. The bit map generated is then used to compress each of the R, G, and B signals separately, removing the intercolor correlations. The weighted trichromatic signal is generated by properly weighting R, G, and B signals so that the reconstructed R, G, and B signals have minimum mean square error (MSE). Another approach using a bit-wise majority rule on the R, G, and B BTC bit maps is also discussed. The algorithm preserves the spatial details in the image content and has low computational complexity. An 8:1 compression can be achieved. >

Multispectral image processing of paintings

Abstract A reflectographic apparatus, equipped with an image processor, has been used to obtain a trichromatic image of paintings comprehensive of both visible and infrared (700–1000nm) regions. The first step has been to reproduce with MIPP (multispectral image processing of paintings) images similar to those obtained with IR Kodak colour film. A good discrimination of both pigments and overpainting is possible with this technique which operates in a more flexible and powerful way than IR ‘false colour’ photography. Results are shown relative to a test panel and a tempera painting with extensive overpaint. The possibility of utilizing this technique to correlate a single pigment with its MIPP image is now under investigation.