Re: removing predictable crap from poor quality jpegs

From	Phil Carmody <thefatphil_demunged@yahoo.co.uk>
Newsgroups	comp.compression
Subject	Re: removing predictable crap from poor quality jpegs
Date	2011-05-03 18:03 +0300
Organization	A noiseless patient Spider
Message-ID	<87y62nx1vx.fsf@bazspaz.fatphil.org> (permalink)
References	<877ha8xeex.fsf@bazspaz.fatphil.org> <06670647-eea6-489e-8ec2-ec89d1e712cf@j28g2000vbp.googlegroups.com>

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Sebastian <s.gesemann@gmail.com> writes:

> On 3 Mai, 12:32, Phil Carmody wrote:
> >
> > http://fatphil.org/images/crappyjpg.jpg
> >
> > Is there any simple fix to remove the chessboarding? It seems obvious
> > that the chessboarding is the (8,8) coefficient in the DCT, so perhaps
> > I just need to strip all non-zero (8,8) coefficients from the file. Is
> > there a utility that can do that? One that otherwise doesn't change
> > the file would be best.
> 
> I don't know of a tool that does that. But I agree with you that it
> should do the trick in theory.
> 
> > One idea was to use jpegtran -scale 7/8 | jpegtran -scale 8/7 to
> > just remove all of the (x,8) and (8,y) coefficients. Which is more
> > than I need, but probably causes no losses of other frequencies that
> > I would object to. Can anyone see any downsides to that? (The results
> > look like an improvement to me.)
> 
> I think a "normal lowpass filter" is preferable. Scaling twice
> involves a bit of aliasing

How can it? Only the frequencies we're interested in are preserved on 
scaling down, and no frequencies we're not interested in are introduced
on scaling up. The operation's purely done in frequency-space. 

> and imaging and if you want to do it
> correctly, also lowpass filtering. Just skip the resampling part and
> apply a lowpass directly.
> 
> In case you have Matlab or Octave, I would recomment a 2nd order
> Butterworth filter that is applied bidirectionally -- first in one
> dimension, then in the other. This way, you have a great control over
> the cutoff frequency and it's fast.
> 
> As an alternative, a FIR filter might do. Photoshop as well as Gimp
> allows you to enter filter coefficients (5x5 or even 7x7). You could
> try to create a filter that specifically removes the checkerboard:
> 
>   -1     3    -4     3    -1
>    3    -9    12    -9     3
>   -4    12   128    12    -4
>    3    -9    12    -9     3
>   -1     3    -4     3    -1
> 
> (Divisor: 144)
> 
> This should not blur the image too much but mostly get rid of
> checkerboard artefacts.

I did consider such a filter (or similar). A quick run of the noise
reduction function in graphicsmagick (or whatever it's called) wasn't 
able to completely remove the checkerboard. It of course removed 
different noise types all over the image, which isn't a bad thing. 

However, I preferred to just address the artefacts I considered to
be the 'bug', as I didn't want to throw away anything I didn't need
to.

> > On an 'implementation' note, it does look like that noise is a
> > programmatic error in the original jpeg compression code (I have no
> > idea what created it) rather than some horrific scanner/scaling/aliasing
> > artefact.
> 
> I think there was lots of high energy noise in the original image.
> Strong compression means coarse quantization. Sometimes the high
> frequency coefficient (8,8) was quantized to zero and sometimes it got
> quantized to some larger nonzero coefficient.

Could be. Thanks for your input.

Phil
-- 
"At least you know where you are with Microsoft."
"True. I just wish I'd brought a paddle." -- Matthew Vernon

Thread

removing predictable crap from poor quality jpegs Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-05-03 13:32 +0300
  Re: removing predictable crap from poor quality jpegs human <noreply@elfavo.com> - 2011-05-03 13:53 +0200
    Re: removing predictable crap from poor quality jpegs Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-05-03 16:09 +0100
      Re: removing predictable crap from poor quality jpegs human <noreply@elfavo.com> - 2011-05-03 18:10 +0200
        Re: removing predictable crap from poor quality jpegs human <noreply@elfavo.com> - 2011-05-03 18:32 +0200
  Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-03 06:22 -0700
    Re: removing predictable crap from poor quality jpegs Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-05-03 18:03 +0300
      Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-05 04:18 -0700
        Re: removing predictable crap from poor quality jpegs human <noreply@elfavo.com> - 2011-05-05 13:35 +0200
          Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-06 00:23 -0700
            Re: removing predictable crap from poor quality jpegs human <noreply@elfavo.com> - 2011-05-06 14:24 +0200
              Re: removing predictable crap from poor quality jpegs Thomas Richter <thor@math.tu-berlin.de> - 2011-05-06 20:33 +0200
                Re: removing predictable crap from poor quality jpegs human <noreply@elfavo.com> - 2011-05-08 09:52 +0200
                Re: removing predictable crap from poor quality jpegs Thomas Richter <thor@math.tu-berlin.de> - 2011-05-08 15:27 +0200
                Re: removing predictable crap from poor quality jpegs human <noreply@elfavo.com> - 2011-05-08 17:55 +0200
                Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-08 07:56 -0700
                Re: removing predictable crap from poor quality jpegs human <noreply@elfavo.com> - 2011-05-08 18:44 +0200
                Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-08 10:21 -0700
                Re: removing predictable crap from poor quality jpegs human <noreply@elfavo.com> - 2011-05-09 10:51 +0200
                Re: removing predictable crap from poor quality jpegs Thomas Richter <thor@math.tu-berlin.de> - 2011-05-09 11:49 +0200
                Re: removing predictable crap from poor quality jpegs human <noreply@elfavo.com> - 2011-05-09 12:06 +0200
                Re: removing predictable crap from poor quality jpegs Thomas Richter <thor@math.tu-berlin.de> - 2011-05-09 15:29 +0200
                Re: removing predictable crap from poor quality jpegs Guido Vollbeding <gv@uc.ag> - 2011-05-09 16:03 +0200
                Re: removing predictable crap from poor quality jpegs human <noreplay@elfavo.com> - 2011-05-09 22:01 +0200
                Re: removing predictable crap from poor quality jpegs Thomas Richter <thor@math.tu-berlin.de> - 2011-05-09 23:24 +0200
                Re: removing predictable crap from poor quality jpegs human <noreplay@elfavo.com> - 2011-05-10 16:45 +0200
                Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-09 04:15 -0700
                Re: removing predictable crap from poor quality jpegs human <noreplay@elfavo.com> - 2011-05-09 14:26 +0200
                Re: removing predictable crap from poor quality jpegs Thomas Richter <thor@math.tu-berlin.de> - 2011-05-09 15:51 +0200
                Re: removing predictable crap from poor quality jpegs human <noreplay@elfavo.com> - 2011-05-09 21:09 +0200
                Re: removing predictable crap from poor quality jpegs Thomas Richter <thor@math.tu-berlin.de> - 2011-05-09 22:28 +0200
                Re: removing predictable crap from poor quality jpegs human <noreplay@elfavo.com> - 2011-05-09 23:06 +0200
                Re: removing predictable crap from poor quality jpegs Thomas Richter <thor@math.tu-berlin.de> - 2011-05-10 17:34 +0200
                Re: removing predictable crap from poor quality jpegs human <noreplay@elfavo.com> - 2011-05-12 15:01 +0200
                Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-09 09:40 -0700
                Re: removing predictable crap from poor quality jpegs human <noreplay@elfavo.com> - 2011-05-09 20:23 +0200
                Re: removing predictable crap from poor quality jpegs Thomas Richter <thor@math.tu-berlin.de> - 2011-05-09 22:37 +0200
                Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-10 02:27 -0700
                Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-10 05:01 -0700
                Re: removing predictable crap from poor quality jpegs human <noreplay@elfavo.com> - 2011-05-12 15:51 +0200
                Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-13 05:07 -0700
                Re: removing predictable crap from poor quality jpegs human <noreplay@elfavo.com> - 2011-05-13 14:39 +0200
                Re: removing predictable crap from poor quality jpegs human <noreplay@elfavo.com> - 2011-05-13 15:39 +0200
                Re: removing predictable crap from poor quality jpegs human <noreplay@elfavo.com> - 2011-05-13 16:36 +0200
                Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-13 08:52 -0700
                Re: removing predictable crap from poor quality jpegs human <noreplay@elfavo.com> - 2011-05-13 19:00 +0200
                Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-13 10:07 -0700
                Re: removing predictable crap from poor quality jpegs human <noreplay@elfavo.com> - 2011-05-13 17:25 +0200
                Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-13 10:06 -0700
                Re: removing predictable crap from poor quality jpegs Pete Fraser <pfraser@covad.net> - 2011-05-13 18:17 -0700
                Re: removing predictable crap from poor quality jpegs Guido Vollbeding <guido@jpegclub.org> - 2011-05-14 09:16 +0200
                Re: removing predictable crap from poor quality jpegs Guido Vollbeding <guido@jpegclub.org> - 2011-05-14 10:07 +0200
                Re: removing predictable crap from poor quality jpegs Guido Vollbeding <guido@jpegclub.org> - 2011-05-14 19:52 +0200
                Re: removing predictable crap from poor quality jpegs Guido Vollbeding <guido@jpegclub.org> - 2011-05-14 21:08 +0200
                Re: removing predictable crap from poor quality jpegs Guido Vollbeding <guido@jpegclub.org> - 2011-05-16 08:43 +0200
                Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-16 05:15 -0700
                Re: removing predictable crap from poor quality jpegs Thomas Richter <thor@math.tu-berlin.de> - 2011-05-16 17:00 +0200
                Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-16 13:02 -0700
                Re: removing predictable crap from poor quality jpegs Thomas Richter <thor@math.tu-berlin.de> - 2011-05-17 09:43 +0200
                Re: removing predictable crap from poor quality jpegs Sebastian <s.gesemann@gmail.com> - 2011-05-19 02:55 -0700
                Re: removing predictable crap from poor quality jpegs Noob <root@127.0.0.1> - 2011-05-20 13:23 +0200
                Re: removing predictable crap from poor quality jpegs Pete Fraser <pfraser@covad.net> - 2011-05-20 05:38 -0700
                Re: removing predictable crap from poor quality jpegs human <noreplay@elfavo.com> - 2011-05-12 20:15 +0200

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