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Old 22 November 2005, 00:39   #1
Codetapper
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Question Algorithm to double the size of a tile based picture smoothely?

A few years back I found a website with information about smoothening out a bitmap picture when you doubled it in size. It doesn't work on photos etc, but for old games with limited palettes it worked very well.

A normal program that doubles will give very chunky pixels. Most programs like Photoshop end up with a smoother picture, but far less crisp and the edges are kind of blurry. If you sharpen you get weird looking edges.

A website I visited had some information about a 2x2 filter which worked on pictures with a low number of colours and would do some tricks such as interpolating pixels based on the adjacent pixels. For example, if you have a picture which is 2x2 pixels where the numbers 1 and 2 represent a colour, and you wish to double the picture to 4x4 pixels:

Code:
12
21

(double)

1122
1122
2211
2211

(apply 2x2 filter)

1122
1222  <- extra 2 inserted over a 1
2221  <- extra 2 inserted over a 1
2211
The algorithm was something like the above, where it would copy a pixel if it was found diagonally, or below and to the right etc, producing a much more smooth picture but with the same number of colours as the original.

I think there was a 4x4 version aswell which ran the 2x2 process twice. It might have been something that is in an emulator or MAME or something.

Does anyone recognise this, know a website detailing this process or know exact what it's called etc? I cannot find the site anymore and want to check out exactly what they did!
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Old 22 November 2005, 00:47   #2
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This one: http://scale2x.sourceforge.net/ ? There are others too, like Eagle or SuperSai.
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Old 22 November 2005, 00:59   #3
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Legend! That's it! Thanks Duke!
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Old 22 November 2005, 09:14   #4
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nice info. Shouldn't this thread be put somewhere else, so it's not deleted. Think this is usefull info
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Old 22 November 2005, 09:24   #5
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wow, why has'nt this evolved into a standard in graphic programs like Photoshop?
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Old 24 November 2005, 01:45   #6
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Because Photoshop is primarily designed to work with high-res, continous tone, true colour images (ie, photos) and this scaling effect is usless for such imagery.
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Old 24 November 2005, 06:24   #7
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Quote:
Originally Posted by Codetapper
I think there was a 4x4 version aswell which ran the 2x2 process twice. It might have been something that is in an emulator or MAME or something.
You do know that WinUAE includes the Scale2x algorithm among the handful of different filters it provides, right? If you're looking for examples of it's use, you might want to look at how it is implemented in the WinUAE source code.
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Old 24 November 2005, 08:31   #8
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Quote:
Originally Posted by Gambit37
Because Photoshop is primarily designed to work with high-res, continous tone, true colour images (ie, photos) and this scaling effect is usless for such imagery.
Yes, but would'nt this techniqe make better images when doing digital zoom (opposed to optical zoom). If you zoom a picture beyond its quality, you will eventually see the pixels. By using this simple (?) method, the illusion of a better picture would be present a bit further...
The method is fairly simple, and not limitied to numbers of colours?
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Old 31 January 2006, 02:46   #9
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Please visit this site, too. IMHO it's the algorithm with the highest quality for increasing sizes of pixeled/paletted images.

http://www.hiend3d.com/
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Old 31 January 2006, 04:36   #10
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The example gfx on the sourceforge website impressed me. Metal Slug rocks! Does anyone know how winuae is using this? It is the "Display->Line Mode->Doubled" option?
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