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Evas filters: Improve RGBA to alpha conversion (visual quality) 

Add weights to the R,G,B components when converting to greyscale.
The weights are those used in the RGB to YCbCr conversion formula.
This commit is contained in:
Jean-Philippe Andre 2014-02-24 13:54:30 +09:00
parent 7a7738e9bb
commit a9558235f6
1 changed files with 14 additions and 5 deletions
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19
src/lib/evas/filters/evas_filter_blend.c
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@ -2,6 +2,9 @@
#include "evas_filter_private.h"
#include "evas_blend_private.h"
// Use a better formula than R+G+B for rgba to alpha conversion (RGB to YCbCr)
#define RGBA2ALPHA_WEIGHTED 1
#if DIV_USING_BITSHIFT
static int
_smallest_pow2_larger_than(int val)
@ -177,7 +180,16 @@ _image_draw_cpu_rgba2alpha(void *data EINA_UNUSED, void *context EINA_UNUSED,
DATA32* srcdata = src->image.data;
DATA8* dstdata = dst->mask.data;
int x, y, sw, dw;
DEFINE_DIVIDER(3);
#if RGBA2ALPHA_WEIGHTED
const int WR = 299;
const int WG = 587;
const int WB = 114;
#else
const int WR = 1;
const int WG = 1;
const int WB = 1;
#endif
DEFINE_DIVIDER(WR + WG + WB);
EINA_SAFETY_ON_FALSE_RETURN_VAL((src_w == dst_w) && (src_h == dst_h), EINA_FALSE);
@ -191,10 +203,7 @@ _image_draw_cpu_rgba2alpha(void *data EINA_UNUSED, void *context EINA_UNUSED,
DATA32 *s = srcdata + src_x;
DATA8 *d = dstdata + dst_x;
for (x = src_w; x; x--, d++, s++)
{
// TODO: Add weights like in YUV <--> RGB?
*d = DIVIDE(R_VAL(s) + G_VAL(s) + B_VAL(s));
}
*d = DIVIDE((R_VAL(s) * WR) + (G_VAL(s) * WG) + (B_VAL(s) * WB));
srcdata += sw;
dstdata += dw;
}