forked from KolibriOS/kolibrios
71 lines
2.4 KiB
Plaintext
71 lines
2.4 KiB
Plaintext
hqx Library README
|
|
==================
|
|
|
|
Introduction
|
|
------------
|
|
hqx is a fast, high-quality magnification filter designed for pixel art.
|
|
|
|
Install
|
|
-------
|
|
NOTE: DevIL library and development headers are required.
|
|
|
|
./configure
|
|
make && make install
|
|
|
|
For more information refer to INSTALL.
|
|
|
|
Usage
|
|
-----
|
|
hqx -s scaleBy input output
|
|
Where scaleBy is either 2, 3 or 4
|
|
|
|
For example:
|
|
hqx -s 4 test.png out.png
|
|
|
|
Example
|
|
-------
|
|
#include <stdint.h>
|
|
#include <hqx.h>
|
|
|
|
uint32_t *src; // Pointer to source bitmap in RGB format
|
|
size_t width, height; // Size of source bitmap
|
|
|
|
/*
|
|
* Code to init src, width & height
|
|
*/
|
|
|
|
uint32_t *dest = (uint32_t *) malloc(width * 4 * height * 4 * sizeof(uint32_t));
|
|
hqxInit();
|
|
hq4x_32(src, dest, width, height);
|
|
|
|
Implementation
|
|
--------------
|
|
The first step is an analysis of the 3x3 area of the source pixel. At first, we
|
|
calculate the color difference between the central pixel and its 8 nearest
|
|
neighbors. Then that difference is compared to a predefined threshold, and these
|
|
pixels are sorted into two categories: "close" and "distant" colored. There are
|
|
8 neighbors, so we are getting 256 possible combinations.
|
|
|
|
For the next step, which is filtering, a lookup table with 256 entries is used,
|
|
one entry per each combination of close/distant colored neighbors. Each entry
|
|
describes how to mix the colors of the source pixels from 3x3 area to get
|
|
interpolated pixels of the filtered image.
|
|
|
|
The present implementation is using YUV color space to calculate color
|
|
differences, with more tolerance on Y (brightness) component, then on color
|
|
components U and V. That color space conversion is quite easy to implement if
|
|
the format of the source image is 16 bit per pixel, using a simple lookup table.
|
|
It is also possible to calculate the color differences and compare them to a
|
|
threshold very fast, using MMX instructions.
|
|
|
|
Creating a lookup table was the most difficult part - for each combination the
|
|
most probable vector representation of the area has to be determined, with the
|
|
idea of edges between the different colored areas of the image to be preserved,
|
|
with the edge direction to be as close to a correct one as possible. That vector
|
|
representation is then rasterised with higher (3x) resolution using
|
|
anti-aliasing, and the result is stored in the lookup table.
|
|
|
|
The filter was not designed for photographs, but for images with clear sharp
|
|
edges, like line graphics or cartoon sprites. It was also designed to be fast
|
|
enough to process 256x256 images in real-time.
|