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P45+ colour rendition - Another test based on IT 8.7

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P45+ colour rendition
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Imatest colour rendition diagrams
Another test based on IT 8.7
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I bought one of Wolf Faust's IT 8.7 targets and photographed it under studio flash lighting on both P45+ and Sony Alpha 99 SLT.

The merit of this test is that the reference target is different from the ColorChecker that calibration normally is made against, but also that many more fields are tested. The disadvantage is that the test target has a small colour space. A short description of the set up is given at the end of this page.

The raw images were developed using Capture One 7.2 and Lightroom 5.3. The table below shows the CIEDE 2000 DeltaE* values.

raw conversionP45+SLT99
Capture One FC5.175.4
Capture One linear3.474.54

Based on these tests I would say that there C1 with linear profile is slightly more accurate than LR5.3 for the P45+, but LR5.3 is significantly more accurate on the SLT 99. My guess is that the use of linear profile with C1 reduces the error in the L-coordinate.

DxO mark reports someting kalled SMI (Sensor Metamerism Index) this is measured on 8 or 16 patches of the ColourChecker under a given illumination and measures the capability of the sensor to produce a metameric match for those colours. It is calculated 100 - 5.5 Delta E* (mean). (needs to be checked). I calculated a "fake" SMI from my Delta E values.

The most accurate conversions were:

  • P45+: Capture One linear profile
  • Sony Alpha SLT 99: LR5.3 with 132525 DCP profile

These two conversions are compared below, P45+ left SLT 99 right. Delta E* > 5 marked red

The image below shows the same conversion P45+ left and SLT 99 right, but with Delta E* > 3 marked in red

The last comparison is between P45+ converted with "film curve" and P45+ converted with my 131225 profile. In this case the LR 5.3 conversion is slightly better.

The impression I have from this test is that the Sony SLT 99 renders more accurate colours than the P45+, regardless the tool used. It also seems that the SLT 99 is considerable more accurate using LR5.3 conversion than using Capture One conversion.

The setup of the experiment

An IT 8.7 from Wolf faust was used. This was printed on matt Kodak paper. The target was accompanied by a CD containing a CGATS file describing the target. The data were mesaured for that batch of the taget but not individually measured.

The test target was set up alongside with a colour checker. Background was gery, and illumination was a Two Elinchrome D-Lite 4 flash flashes with soft boxes. Illumination was measured with a Minolta Flash Meter F and found to vary 0.1-0.2 EV max over the area.

A series of exposures were made and a an exposure selected that was well below clipping (1EV below). 

Raw processing was done so WB was set on the second brightest white patch on the colour checker taht also was used to adjust exposure. "Exposure" was adjusted so second brightest pathch had a Lab value of 0.80 in LR and RGB (200, 200, 200) in C1. In LR "Blacks" slider was adjusted to +25. 

Blacks were left as is in C1. When using "linear curve" in C1, all the gray patches had correct RGB values.

The two images were processed into 16 bits TIFF in Prophoto RGB. Patches were readout in CGATS format using Argyll CMS's "scanin -o " option. These files were loaded into Babelcolor's "Patchtool" and compared against CGATS data for the IT-8 target-

Last Updated on Sunday, 09 March 2014 21:24  


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