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c. Post-processing Reflected Images
i. Correction of Visible-reflected Images
The workflow for the correction of visible-reflected (VIS) images is designed to carry out
correction for the factors affecting visible-reflected images, as summarised in Table 3-1 and
discussed in Chapter 1, and using the data collected as a result of the acquisition protocols
outlined in Chapter 2. Figure 3-19 shows a schematic of the workflow developed in the nip2
software indicating the transformations/corrections to be applied.
bs 00. = 000
Camera output XYZ Flat fielded XYZ Flat fielded sRGB Flat
converted from RAW + colour fielded + colour
calibrated calibrated
Camera Output
Icc Icc
profile profile
Correct for Spectral density
Converts VIS image Correct for spatial c fo
to linear light (XYZ) inhomogeneities orrect for camera
of light source response .
(Flat fielding) (colour calibration)
Figure 3-19. Workflow for the correction of visible-reflected images in the nip2 post-processing
workspace.
The workflow is composed of the following steps:
1) Loading the input images converted from RAW:
— VIS image (with Macbeth chart) and associated VIS flat-field image (if available) for
generating the calibration.
— VIS image to be calibrated (can be the same as above image or another image taken
with the same camera and under the same lighting conditions) and associated VIS flat¬
field image (if available).
2) Converting the images to linear light (XYZ) using the embedded ICC profiles.
3) Applying a flat-field correction to the images (if this option is checked).
4) Straightening and extracting the Macbeth chart from the linearized, flat-field corrected
(flat-fielded) VIS image used to generate the calibration.
5) Generating a colour calibration matrix:
— Sets brightness (luminance) of the image from the Macbeth chart greyscale
— Generates a colour calibration matrix from a linear regression.
6) Applying the colour calibration to the VIS image to be calibrated (based on the
calibration matrix generated from the Macbeth chart).
7) Applying an output ICC profile which converts the linearized, flat-fielded, colour¬
calibrated VIS image to sRGB (or RGB16) colour space.
8) Saving the sRGB (or RGB16) flat-fielded, colour-calibrated VIS image.
Version No. 1.0 122 Date : 14/10/2013