Friday, August 11, 2017

Dexter image quality bug discovered, fix is available now!

I've suspected for a while that something was a little off with Dexter's image quality.  However, this is almost unnoticeable on a CRT, so I haven't prioritized investigating it.  Now that I am trying to finish Star Rider support, which relies on data being decoded from the video signal, I looked into video quality issues further and found a couple of minor problems.

After some troubleshooting, I found that there are two issues with Dexter's image quality:
1) the video is shifted one line from what it should be,
2) the video has an unfocused look

Issue #1 is caused by the raspberry pi itself.  I don't have a "proper" fix, but I can compensate by shifting the video 1 line within the Dexter software which seems to do the trick.

Issue #2 is caused because I am using bilinear filtering inside of the OpenGLES2 code that Dexter is using.  Combined with my shader to implement interlaced video, this was creating a bunch of subtle artifacts that give the unfocused look.  I turned off the bilinear filtering and that did the trick!

I've fixed both of these issues internally and am working on a public fix for everyone.  It will be free for all Dexter customers, new and old.

UPDATE: the fix is live now! :)

Here are two images showing before and after.


After (ignore the extra text)

Please ignore the "Current video line shift" and "Scale factor" text in the second screenshot.  Those are debug messages that I added while troubleshooting this problem.

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