Copy of an X-Rite ColorChecker and a Q-13 Grey Scale, taken with the Pentax K-1 and a Schneider-Kreuznach HM 4.5/90mm lens under cross-polarized illumination with two Walimex Niova 600 Plus Daylight LED light panels. The ColorChecker part serves for making a calibrated linear DNG profile, to be used in the Raw conversion process. The profile is generated with the Adobe DNG Profile Editor, version 1.0.0.47 beta. The grey scale is used to determine the best exposure. The complete workflow involves: (1) Raw conversion of the DNG files in Adobe Camera Raw with the calibrated linear profile and white balance values based on the M patch of the grey scale; (2) applying a flat frame in order to compensate for uneven illumination and lens vignetting; (3) applying a contrast curve in Photoshop with approximate RGB target values (in AdobeRGB) of 245/245/245 for the A patch, 118/118/118 for the M patch and 17/17/17 for the 19 patch (slight deviations are allowed because the grey scale is not always perfectly neutral). All values in these processing steps remain the same for one copying session with fixed magnification, f-stop and exposure time, the same lens, and no changes in illumination, and hence can be automated via a Photoshop action. They have to be recalibrated when magnification is changed, except for the white balance. The profile can be reused as long as the illumination remains unchanged; differences in colour rendering of lenses can be compensated for by adjusting the white balance. The processed image files are saved and archived in AdobeRGB (1998) colour space as TIFF files with 16 bits per channel depth in order to allow for further editing without compromising image quality. The image fidelity that can be attained using this workflow with the 36 MP Pentax K-1 in its Pixelshift mode and with suitable lenses is far superior to what most desktop flatbed scanners can deliver. This is due not only to the overall quality of the camera’s output but also to the ability to control and optimize lighting conditions and to control every processing step.

eda – Ethnographisches Datenarchiv/UB Wien eda – Ethnographic Data Archive/Vienna University Library

Digital photography, see description for details