Image Engineering camSPECS User Manual page 28

CTL interpreters and a JSON (JavaScript Object Notation) file that encodes the spectral
sensitivities for use with Raw-to-ACES applications. These are text files that are user-editable to
facilitate the specification of other workflow-specific parameters, but options are provided for:
Exposure headroom specifies in luminance-linear units the amount of encoding range
o
above camera-assumed diffuse white to allow for specular highlights.
White Balance is the factor required to balance the camera channels to diffuse white.
o
The default values are computed from the integral of the spectral sensitivities.
Luminance creates a transform optimized to the CIE luminosity function (Y) without regard to colorimetric
performance and assuming equal energy illumination (E).
3. Select the desired Reference illuminant spectral distribution file for the scene's light source adopted
white point. For respective light sources, see chapter 0, item 1.
4. Select the desired Profile Type as described above.
5. Select reflectance Training data. The resulting camera transforms will be optimized for the selected
combination of Camera Spectral Sensitivities and the Reference illuminant, which minimizes errors in
predicting the Training data. The data are spectra between 380 and 730 nm in 5 nm increments. Other
data apart from ColorChecker data can be used, for example, iQ in-situ data (see chapter 4.11). New
files can be added to the corresponding directory in the camSPECS software
(/calibration_files/reflectance). Make sure to restart camSPECS to use the new files in this menu. An
optimal camera can be built by obtaining the in-situ data and installing it in the C:/Program Files/Image
Engineering/ camSPECS folder.
6. Select the desired reflectance Test data that will be used to evaluate the camera transform. The test data
is evaluated through the transform, and the results are written to the log file ctbErrorsCIECAM16 once
the camera transform has been computed.
7. Optionally, Additional Test Data can be selected to input additional test spectra to be used to evaluate the
camera transform.
8. Click Start to generate the specified transform.
9. The results panel shows the performance of the transform. By default, a visual representation of the Test
data is shown in a split field for each color patch. The left field for each patch shows the original color,
and the right field shows the color resulting from the transform applied to the original color spectra,
assuming the display is calibrated to the sRGB standard. The numerical values show the CIECAM16
color differences between the two fields.
10. The display shows the results from the computed transform in several forms:
•
Delta E – Color Comparison is the default described in step 9 above.
•
Delta E – Heat Map shows the results categorized and color-coded per the maximum user-specified
tolerance in Delta E range.
•
Spectral response comparison shows the CIE 1931 standard colorimetric observer color matching
functions, the camera spectral sensitivities, and the prediction of the color matching functions
resulting from applying the transform to the camera spectral sensitivities.
Image Engineering
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