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Add support for colour JPEG images.

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I used the luminance match algorithm for converting RGB colour images to
grayscale as it gives the best visual results (but at the cost of speed).
This commit is contained in:
Tigran Aivazian
2012-10-11 22:01:26 +01:00
committed by Qingping Hou
parent 2103461a43
commit cac63cd390
1 changed files with 36 additions and 6 deletions
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42
pic.c
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@@ -102,6 +102,25 @@ uint8_t *readJPEG(const char *fname, int *width, int *height, int *components)
return (uint8_t *)image_buffer;
}
/* Uses luminance match for approximating the human perception of colour,
* as per http://en.wikipedia.org/wiki/Grayscale#Converting_color_to_grayscale
* L = 0.299*Red + 0.587*Green + 0.114*Blue */
static uint8_t *rgbToGrayscale(uint8_t *image, int width, int height)
{
int x, y;
uint8_t *buf = malloc(width*height+1);
if (!buf) return NULL;
for (x = 0; x<width; x++)
for (y=0; y<height; y++) {
int pos = 3*(x+y*width);
buf[x+y*width] = (uint8_t)(0.299*((double)image[pos]) + 0.587*((double)image[pos+1]) + 0.114*((double)image[pos+2]));
}
return buf;
}
static int openDocument(lua_State *L) {
int width, height, components;
const char *filename = luaL_checkstring(L, 1);
@@ -110,18 +129,27 @@ static int openDocument(lua_State *L) {
luaL_getmetatable(L, "picdocument");
lua_setmetatable(L, -2);
unsigned char *image = readJPEG(filename, &width, &height, &components);
if (!image)
return luaL_error(L, "cannot open jpeg file");
uint8_t *raw_image = readJPEG(filename, &width, &height, &components);
if (!raw_image)
return luaL_error(L, "Cannot open jpeg file");
if (components != 1)
if (components == 1)
doc->image = raw_image;
else if (components == 3) {
uint8_t *gray_image = rgbToGrayscale(raw_image, width, height);
if (!gray_image) {
free(raw_image);
return luaL_error(L, "Cannot convert to grayscale");
} else {
free(raw_image);
doc->image = gray_image;
}
} else
return luaL_error(L, "Unsupported image format");
doc->image = image;
doc->width = width;
doc->height = height;
doc->components = components;
//printf("openDocument(%s) decoded image: %dx%dx%d\n", filename, width, height, components);
return 1;
}
@@ -132,6 +160,7 @@ static int openPage(lua_State *L) {
PicPage *page = (PicPage*) lua_newuserdata(L, sizeof(PicPage));
luaL_getmetatable(L, "picpage");
lua_setmetatable(L, -2);
page->width = doc->width;
page->height = doc->height;
page->doc = doc;
@@ -158,6 +187,7 @@ static int closeDocument(lua_State *L) {
return 0;
}
/* uses very simple nearest neighbour scaling */
static void scaleImage(uint8_t *result, uint8_t *image, int width, int height, int new_width, int new_height)
{
int x, y;