Scale2x

Scale2x, Scale3x and Scale4x are real-time graphics effects able to increase the size of small bitmaps by guessing the missing pixels without blurring the images.

They were originally developed for the AdvanceMAME project in the year 2001 to improve the quality of old games running at low video resolutions. The specification of the algorithm and more details are at:

https://www.scale2x.it

This package contains some implementations of the effects in C and SSE2 intrinsics, and command line tools to convert manually .PNG images.

IMPLEMENTATION

The files scale2x.c and scale3x.c are the fast C and SSE2 implementations of the effects.

The files scalebit.c and scalebit.h are the fast C implementations of the effects ready to be applied to a generic bitmap.

Note that the implementation of the Scale4x effect is not obvious without using a big intermediate buffer.

The file scalerx.c is a simple command line processor, which uses the reference implementation of the effects.

The file scalex.c is another simple command line processor, which uses the fast implementation of the effects.

TOOLS

The command line tools "scalerx" and "scalex" read a .PNG file and write another .PNG file with the effect applied. The syntax of the programs is:

scalerx [-k N] [-w] FROM.png TO.png
scalex [-k N] FROM.png TO.png

The option -k can be used to select the scale factor. The option -w can be used to scale textures with a wraparound effect. To compile the command line tools you need the libz and libpng libraries.

EXAMPLES

The directory example/ contains some examples of the effects applied to a generic image and to a test image. The suffix of the images means:

1 - Original image.
2 - Scale2x effect.
3 - Scale3x effect.
4 - Scale4x effect.
1x - Scaled normally 12 times.
2x - Scale2x effect and scaled normally up to 12 times.
3x - Scale3x effect and scaled normally up to 12 times.
4x - Scale4x effect and scaled normally up to 12 times.

The 'x' images have the same final size and can be used to compare pixel by pixel the result of the effects.