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We audiophiles are not the only hobbyists with issues......


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I came across a fascinating article posted on the photography site on which I'm a long time participant (photo.net) . It's not unlike the AS community - I've always enjoyed my interaction with the many useful, educational, and entertaining participants and even some of the usual assortment of issue-driven people.  I think this was posted as a bridge between humor and the quandry of finding and using objective testing to judge the quality of equipment.  I suspect it will stir up a bit of laughter, a bit of interest, and more than a bit of controversy.  There might even be similar "tests" in use by audiophiles.

 

Click HERE to learn about "the brick wall test".

 

[PS:  Yes, it was an April Fool's post - but not everyone posting in response to it seems to have known that.  So there are some responses that could just as easily have been found right here 😉 ]

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I use ColorChecker Classic instead of brick wall and Matlab Image Processing Toolbox measureColor() and imapplymatrix() to correct color appearance of photos, when it is necessary.

 

To get lens distortion parameters and undistort photos, I take multiple images of DIY A4 size Checkerboard and Single Camera Calibrator app of Matlab Computer Vision Toolbox. There is OpenCV alternative and it is free.

Sunday programmer since 1985

Developer of PlayPcmWin

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On 4/26/2021 at 5:51 AM, yamamoto2002 said:

I use ColorChecker Classic instead of brick wall and Matlab Image Processing Toolbox measureColor() and imapplymatrix() to correct color appearance of photos, when it is necessary.

 

The freely available X-Rite ColorChecker Camera Calibration is supposed to be able to generate DNG/ICC camera profiles from many ColorChecker variants. Wouldn't that do? Back in the DNG Profile Manager days, one can give it two calibration photos at different light source color temperature and it's said that Lightroom can then interpolate across the whole input image color temperature range based on the resulting DNG profile. The same should be in the current generation.

 

Quote

To get lens distortion parameters and undistort photos, I take multiple images of DIY A4 size Checkerboard and Single Camera Calibrator app of Matlab Computer Vision Toolbox. There is OpenCV alternative and it is free.

 

Wouldn't lens distortion depend on focus distance? PTLens recommends at least 25ft from a building facade with perfect straight lines. And for zooms, 10-12 images with denser distribution on the short side where distortion characteristic changes more quickly.

 

By the way, any before/after demo photos of your process?

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40 minutes ago, accwai said:

By the way, how's the brick wall test below? Is it acceptable by stringent standard of the internet experts?

 

48527545822_c6f2444c0f_c_d.jpg

 

Search me!  I have ebnough trouble finding objective audio measurements 😉

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10 hours ago, accwai said:

The freely available X-Rite ColorChecker Camera Calibration is supposed to be able to generate DNG/ICC camera profiles from many ColorChecker variants. Wouldn't that do? Back in the DNG Profile Manager days, one can give it two calibration photos at different light source color temperature and it's said that Lightroom can then interpolate across the whole input image color temperature range based on the resulting DNG profile. The same should be in the current generation.

 

Matlab solution works well for me. I think X-Rite ColorChecker app is not easy to use, ColorChecker chart detection function sometimes does not work for no reason.😀

 

10 hours ago, accwai said:

Wouldn't lens distortion depend on focus distance? PTLens recommends at least 25ft from a building facade with perfect straight lines. And for zooms, 10-12 images with denser distribution on the short side where distortion characteristic changes more quickly.

 

Yes. I fixed the focal length using permacel tape. Also camera parameter changes when lens is detached and re-attached (optical center is shifted by several dozen pixels). I don't use zoom lens

Sunday programmer since 1985

Developer of PlayPcmWin

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1 hour ago, accwai said:

By the way, how's the brick wall test below? Is it acceptable by stringent standard of the internet experts?

 

48527545822_c6f2444c0f_c_d.jpg

 

IMO a more proper one in case of a music loving photographer :)

 

3657375.jpg

What’s true of all the evils in the world is true of plague as well.
It helps men to rise above themselves.
 
  ―  Albert Camus, The Plague.

 

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  • 2 weeks later...
On 4/27/2021 at 5:12 PM, yamamoto2002 said:

Matlab solution works well for me. I think X-Rite ColorChecker app is not easy to use, ColorChecker chart detection function sometimes does not work for no reason.😀

 

Looks like the X-Rite app is quite finicky about data in the patches. And when it runs into problems, it just tells you something generic like capture size not big enough. The chart function in the Adobe DNG Profile Editor has much more specific error message, down to which patch is causing problem. So running the captures through that could provide some insight. How easy/painful the process is probably depends on the color engine in the specific camera. The before/after DNG profiling below is from a phone:

 

dng_embed.jpg.20c0c0df6cfa587972a977cc243051af.jpg

 

dng_dcp.jpg.c4558905761a9384e3d7d8eb2379d71e.jpg

 

DNG file from the phone is pretty much useless without camera profiling. But the amount of twisting the profile does is quite significant. So even with it, strange behavior could be lurking in the process somewhere. We will see...

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