fast dither

fast dither

Post by Aaron Robinso » Wed, 13 Sep 2000 05:46:57



Im looking for a very fast dither algorithm on an 8-bit "greyscale" array of
pixels

this is for a real time image distortion/blur engine ive been working on,
and speed is much more important than quality.

Thanks in advance,
Aaron [www.caustik.com]

 
 
 

fast dither

Post by Phil McRev » Wed, 13 Sep 2000 02:52:16


[Please do not mail me a copy of your followup]



Quote:>Im looking for a very fast dither algorithm on an 8-bit "greyscale" array of
>pixels

Ordered dither is very fast and is often implemented in hardware for
that reason.  Graphics Gems has an implementation of ordered dither
<http://www.veryComputer.com/>
--
<http://www.veryComputer.com/~legalize/> Legalize *hood!
    ``Ain't it funny that they all fire the pistol,    
      at the wrong end of the race?''--PDBT    
    <http://www.veryComputer.com/~legalize/who/>

 
 
 

fast dither

Post by Aaron Robinso » Wed, 13 Sep 2000 07:49:27


ok, I checked out some pages, and ordered dithering seems to be what I want
to use.

I found a utility that will generate a matrix to use, but i dont know
exactly how the matrix is used.

Any help would be appreciated

aaron [www.caustik.com]


> [Please do not mail me a copy of your followup]



> >Im looking for a very fast dither algorithm on an 8-bit "greyscale" array
of
> >pixels

> Ordered dither is very fast and is often implemented in hardware for
> that reason.  Graphics Gems has an implementation of ordered dither
> <http://www.veryComputer.com/>
> --
> <http://www.veryComputer.com/~legalize/> Legalize *hood!
>     ``Ain't it funny that they all fire the pistol,
>       at the wrong end of the race?''--PDBT
>     <http://www.veryComputer.com/~legalize/who/>

 
 
 

fast dither

Post by Aaron Robinso » Wed, 13 Sep 2000 07:49:45


ok, I checked out some pages, and ordered dithering seems to be what I want
to use.

I found a utility that will generate a matrix to use, but i dont know
exactly how the matrix is used.

Any help would be appreciated

aaron [www.caustik.com]


> [Please do not mail me a copy of your followup]



> >Im looking for a very fast dither algorithm on an 8-bit "greyscale" array
of
> >pixels

> Ordered dither is very fast and is often implemented in hardware for
> that reason.  Graphics Gems has an implementation of ordered dither
> <http://www.veryComputer.com/>
> --
> <http://www.veryComputer.com/~legalize/> Legalize *hood!
>     ``Ain't it funny that they all fire the pistol,
>       at the wrong end of the race?''--PDBT
>     <http://www.veryComputer.com/~legalize/who/>

 
 
 

fast dither

Post by Aaron Robinso » Wed, 13 Sep 2000 07:50:39


ok, I checked out some pages, and ordered dithering seems to be what I want
to use.

I found a utility that will generate a matrix to use, but i dont know
exactly how the matrix is used.

Any help would be appreciated

aaron [www.caustik.com]


> [Please do not mail me a copy of your followup]



> >Im looking for a very fast dither algorithm on an 8-bit "greyscale" array
of
> >pixels

> Ordered dither is very fast and is often implemented in hardware for
> that reason.  Graphics Gems has an implementation of ordered dither
> <http://www.veryComputer.com/>
> --
> <http://www.veryComputer.com/~legalize/> Legalize *hood!
>     ``Ain't it funny that they all fire the pistol,
>       at the wrong end of the race?''--PDBT
>     <http://www.veryComputer.com/~legalize/who/>

 
 
 

fast dither

Post by Phil McRev » Wed, 13 Sep 2000 06:43:55


[Please do not mail me a copy of your followup]



Quote:>ok, I checked out some pages, and ordered dithering seems to be what I want
>to use.

>I found a utility that will generate a matrix to use, but i dont know
>exactly how the matrix is used.

Its in the Graphics Gems I book.
--
<http://www.veryComputer.com/~legalize/> Legalize *hood!
    ``Ain't it funny that they all fire the pistol,    
      at the wrong end of the race?''--PDBT    
    <http://www.veryComputer.com/~legalize/who/>
 
 
 

fast dither

Post by Hans-Bernhard Broeke » Wed, 13 Sep 2000 21:55:48


[Why post the same article thrice? ]


> I found a utility that will generate a matrix to use, but i dont know
> exactly how the matrix is used.

Conceptually: you treat the image in units of the matrix size (8x8
blocks, or whatever size your matrix is). You add the value in the
matrix corresponding to each pixel of the input image, and check if
the result is above or below the threshold. If it is --> ouptut a
white pixel. If it isn't --> output black one. Pseudocode:

outputimage[x][y] =
    floor ((inputimage[x][y] + matrix[x % matrixwith][y % matrixheight])
            / factor);

Essentially, this treats the matrix as a 'noise pattern', and
thresholds the image after addition of that noixe. For an 8x8 matrix
used to dither an 8bit graymap image, the 'factor' would be 1.

--

Even if all the snow were burnt, ashes would remain.

 
 
 

fast dither

Post by Aaron Robinso » Thu, 14 Sep 2000 04:40:30


outlook express claimed the post wasnt sending...so after 3 attempts i found
it was sending all along


> [Why post the same article thrice? ]


> > I found a utility that will generate a matrix to use, but i dont know
> > exactly how the matrix is used.

> Conceptually: you treat the image in units of the matrix size (8x8
> blocks, or whatever size your matrix is). You add the value in the
> matrix corresponding to each pixel of the input image, and check if
> the result is above or below the threshold. If it is --> ouptut a
> white pixel. If it isn't --> output black one. Pseudocode:

> outputimage[x][y] =
>     floor ((inputimage[x][y] + matrix[x % matrixwith][y % matrixheight])
>             / factor);

> Essentially, this treats the matrix as a 'noise pattern', and
> thresholds the image after addition of that noixe. For an 8x8 matrix
> used to dither an 8bit graymap image, the 'factor' would be 1.

> --

> Even if all the snow were burnt, ashes would remain.

 
 
 

fast dither

Post by Steven Greave » Tue, 19 Sep 2000 04:00:00


Quote:> I found a utility that will generate a matrix to use, but i dont know
> exactly how the matrix is used.

What is the utility that generates a matrix ?

Thanks,

Steve

 
 
 

1. Fast dithering algorithm?

I'm currently working on a JPEG viewer for MSDOS. I'm using the
IJG JEPG implementation.
One of the most time consuming parts of the code is the dithering
that is applied after 2-pass Heckbert style quantization.
The dithering is standard FS dithering (sepentine, I think).
The problem is, 1/3 of the display time is the dithering, yet
the difference in quality (dither/no dither) doesn't seem worth the time.

Can anyone give me references to faster (possibly slightly poorer quality)
dithering algorithms??

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