Re: Improving the quality of a blocky image

AJ wrote:
> Hi All,
> 
> I have an image which is very blocky (image can be seen at
> http://img222.imageshack.us/my.php?image=degradedimagesh2.png
) and
> would like to try and improve it's quality as much as possible.
> 
> I understand that the image is of such a poor quality that I do not
> expect any huge improvements - that is not my aim, my aim is to see if
> it can be improved at all, and if so, which method(s) could yield the
> best results.
> 
> So far I have tried some iterative restoration techniques such as
> Richardson-Lucy deconvolution and Blind deconvolution - both have
> proved to give a slight improvement.
> 
> I was hoping someone would have some other suggestions as to how I
> could possibly improve the image.

You could play the match boundary continuity game with a cosmetic 
enhancement. I think the IJG codec can be persuaded to do this with 
suitable options.
> 
> Just in case understanding how the image was degraded in the first
> place might help lead to a good suggestion for improvement algorithms,
> I created the image using the following steps:
> 
> * 8x8 Sub-Block and DCT image
> * store top 2 coefficients from each sub-block
> * use these to create a new image

So your reconstruction is from DC and lowest frequency horizontal 
component only? I don't think you can do much starting from there.

Taking a subset square of low frequency coefficients around the DC 
component would give you a classic undersampling problem. eg 2x2 or 3x3 
measured components. But unless the reconstructed image clips against 0 
or 255 you don't get much by way of clues to regain resolution lost by 
the downsampling. And your test image is well clear of either.

A simple field of white dots on a pure black ground would give you a 
test image where you might stand a better chance of success.

In an ideal world maxent or another optimised nonlinear reconstruction 
might hope to extrapolate resolution to 3x the highest measured 
frequency for regions with the best signal to noise.

Regards,
Martin Brown
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