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| BBC Micro filter for The GIMP http://www.retrosoftware.co.uk/forum/viewtopic.php?f=27&t=531 |
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| Author: | DaveJ [ Fri Nov 12, 2010 4:13 pm ] |
| Post subject: | BBC Micro filter for The GIMP |
Francis' BBC Micro Image Convertor has proved inspirational in these parts - I decided to try doing something similar (but nowhere near as good - or as fast!) as a plug-in for The GIMP: http://kecskebak.blogspot.com/2010/11/bbc-on-bbc.html |
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| Author: | FrancisL [ Wed Nov 24, 2010 3:49 pm ] |
| Post subject: | Re: BBC Micro filter for The GIMP |
Nice work on that, although I'm surprised that you didn't include the Atkinson dithering method (one of my favourites). You can get info on it here: http://www.tinrocket.com/projects/progr ... ics/00158/ Kind regards, Francis |
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| Author: | DaveJ [ Thu Nov 25, 2010 9:16 am ] |
| Post subject: | Re: BBC Micro filter for The GIMP |
The absence of Atkinson is entirely down to laziness on my part - it would be very easy to add, but at the moment I get my divisor by summing the matrix values instead of storing it separately, which I'd need to do for Atkinson.  You're right about Atkinson being good - I've used it a lot in the BBC Micro Image Converter. |
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| Author: | FrancisL [ Thu Nov 25, 2010 11:00 am ] |
| Post subject: | Re: BBC Micro filter for The GIMP |
For Image2BBC I just store the error diffusion matrices as fractions so no need to sum the numbers up and work out the divisor. The only other thing I will say is that because the Atkinson dithering method doesn't diffuse the full error you may hit a problem with your dithering strength algorithm depending on how you have implemented it. If my memory serves I had to do a special exception for Atkinson dithering. Kind regards, Francis |
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| Author: | DaveJ [ Thu Nov 25, 2010 1:05 pm ] |
| Post subject: | Re: BBC Micro filter for The GIMP |
Many thanks for your advice Francis. Now you've pointed it out to me it's obvious that I should store fractions instead of integers for matrix values
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