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Pentax K1 Super Resolution Mode has Color Problems, Definitely an Adobe Camera Raw BUG

See my Pentax K1 wish list at B&H Photo.

Pentax K1 pixel shift settings

UPDATE: the most probable diagnosis seems to be an Adobe Camera Raw bug. The RawDigger histograms are virtually identical for StdRes vs SupeRes. Yet the RGB histograms in Photoshop show that the blue channel is pushed up in luminance in the quarter and half tones (16-bit ProPhotoRGB used for the images). The green channel is also affected. I’ve added those RGB histograms to the page.

I’ve also sent an email to three Adobe engineers; I am hoping the email gets through and gets attention. I don’t have any direct phone contact with appropriate Adobe engineers, so I can’t get any immediate feedback before I leave on my 2 day trip today.

UPDATE: This is what I heard from Adobe: “Known issue. It is fixed in the next ACR update. High ISO dngs shots with super resolution”. That sounds good, but both my examples are at ISO 100, the lowest available ISO.

SuperRes pixel shift mode (“SR-PSM”) merges 4 exposures into one raw file.The raw converter must then take those 4 exposures and (somehow) create an RGB pixel for each pixel in the image.

Pentax K1

It might be assumed that a StdRes image and SuperRes image would have the same color behavior, but this is not so. Possible reasons (and there may be others) include:

  • Changes in lighting (ruled out for this example).
  • Some kind of general bug in the raw converter. Adobe Camera Raw 9.5.1 (595) was used for this example.
  • A bug in the Adobe Camera Raw camera profile used for image conversion and/or the way it is applied for StdRes vs SuperRes mode.
  • A bug in the camera processing.
  • Some unavoidable difference inherent to SuperRes pixel shift mode itself.

The motivation to shoot this test was seeing the same problem seen under other completely different conditions (albeit daylight in all cases)—anytime StdRes mode is compared to SuperRes mode. So this is not a one-off behavior, but a consistent problem.

As demonstrated, color in SuperRes mode is inferior in contrast and color to StdRes mode; a veiling blue haze intrudes. And it is not easy to fix—I did not find a satisfactory solution.

Pentax K1 SuperRes Pixel Shift Mode vs Std Res: Color Innaccuracy

Includes RawDigger histograms.

StdRes mode — color is fine
f8 @ 1/250 sec, ISO 100; 2016-05-12 16:37:47
PENTAX K-1 + HD PENTAX-D FA 15-30mm F2.8 ED SDM WR @ 30mm

[low-res image for bot]
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