Algorithm to double the size of a tile based picture smoothely?

Codetapper · 22 November 2005, 00:39

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!

Duke · 22 November 2005, 00:47

This one: http://scale2x.sourceforge.net/ ? There are others too, like Eagle or SuperSai.

Codetapper · 22 November 2005, 00:59

Legend! That's it! Thanks Duke!

Dizzy · 22 November 2005, 09:14

nice info. Shouldn't this thread be put somewhere else, so it's not deleted. Think this is usefull info

Haakon · 22 November 2005, 09:24

wow, why has'nt this evolved into a standard in graphic programs like Photoshop?

Gambit37 · 24 November 2005, 01:45

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.

Chuckles · 24 November 2005, 06:24

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.

Haakon · 24 November 2005, 08:31

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?

Feltzkrone · 31 January 2006, 02:46

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/

Adderly · 31 January 2006, 04:36

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?

22 November 2005, 00:39	#1
Codetapper Moderator Join Date: May 2001 Location: Auckland / New Zealand Age: 38 Posts: 2,465	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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22 November 2005, 00:47	#2
Duke HOL-Team Join Date: Apr 2002 Location: Germany Age: 32 Posts: 515	This one: http://scale2x.sourceforge.net/ ? There are others too, like Eagle or SuperSai.

22 November 2005, 00:59	#3
Codetapper Moderator Join Date: May 2001 Location: Auckland / New Zealand Age: 38 Posts: 2,465	Legend! That's it! Thanks Duke!

22 November 2005, 09:14	#4
Dizzy DEAD Join Date: Jan 2002 Location: . Posts: 3,399	nice info. Shouldn't this thread be put somewhere else, so it's not deleted. Think this is usefull info

22 November 2005, 09:24	#5
Haakon Registered User Join Date: Sep 2004 Location: Norway Age: 38 Posts: 180	wow, why has'nt this evolved into a standard in graphic programs like Photoshop?

24 November 2005, 01:45	#6
Gambit37 Registered User Join Date: Oct 2005 Location: Brighton, England Age: 40 Posts: 25	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.

31 January 2006, 02:46	#9
Feltzkrone Junior Member Join Date: Apr 2002 Location: Germany Posts: 101	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/

31 January 2006, 04:36	#10
Adderly [Satan^God] Join Date: Oct 2005 Location: Germany Posts: 701	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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