English Amiga Board - View Single Post - 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!

22 November 2005, 00:39	#1
Codetapper 2 contact me: email only! Join Date: May 2001 Location: Auckland / New Zealand Posts: 3,182	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!