Biomedical Engineering Reference
In-Depth Information
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FIGURE 16.17
(See color insert) Visualization of the color space for simulated cone responses by using a 5
5 rectangular SOM.
16.5.7
Imaging Spectral Scenes
The PERs and action spectra of the imaging arrays have been measured and their sensitiv-
ities have been calculated. This information enables functional simulation of a theoretical
high-resolution imaging device based on BR. The dynamic range of such a device would be
limited by the number of molecules in the BR elements. Depending on the number of BR
molecules in each array element, shutter mechanism, SNR of the electronics, and resolution
of the analog-to-digital conversion, the dynamic range and number of detectable intensity
levels would be sufficient for general use. To visualize the capabilities of such an imaging
device, two test images were used. The first one was a spectral reflectance image of a
GretagMacBethâ„¢ color-rendition chart (see Figure 16.19a), and the red1 spectral image
from the spectral data set of natural scenes measured at University of Bristol (see Figure
16.19b). The resolutions of the images were 64
256 in the spatial dimension,
whereas the numbers of spectral bands were 151 and 31 (400-700 nm; 2-nm and 10-nm
intervals). The response images in Figure 16.19 show that the imprecision in the measured
action spectra caused limited color discrimination capability. When templates developed
for visual pigments were fitted to the absorption peaks of the three BR types, the result
better represented the true capabilities of the theoretical device. The response together with
an estimated response of cone pigments in the human retina is shown in Figure 16.20. It is
evident that for good color separation, further processing of sensor information is needed.
64 and 256
16.6
Conclusions
Several factors affect and limit the future development of computers based on technolo-
gies in current use. Biomolecules offer an alternative approach to computing, and some of
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