Modification du canal alpha

Malheureusement, il n'y a rien qui gère ça de façon efficace:

Je te propose d'utiliser une fonction que j'ai fait pour ma librairie, ça combine les channels R,G,B de image1 et image2 selon la transparence dans image2.

Code:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
 
/**
* @brief Add src2 on src1 using src2 alpha channel (transparency).
* 
* @code
* foreach(c=channels)
*      dst[I,c] = src1[I,c]*(1-(src2[I,alpha]/255)) + src2[I,c]*(src2[I,alpha]/255)
* end
* @endcode
* 
* @param src1 The first source array (background image, 3 or 4 channels)
* @param src2 The second source array (transparent image, 4 channels minimum)
* @param dst The destination array (merge image, 3 or 4 channels).
* @note This function only works with IPL_DEPTH_8U image for the moment.
*/
void x7sAddAlphaLayer_3C4C8U(const IplImage *src1, const IplImage *src2, IplImage *dst)
{
 
	uint8_t *p_im1, *p_im2,*end,*p_dst;
	int nChan_im1, nChan_dst, c;
	float tmp, ratio;
 
 
	//Set the pointers.
	p_im1 =  (uint8_t*)src1->imageData;
	p_im2 =  (uint8_t*)src2->imageData;
	p_dst = (uint8_t*)dst->imageData;
	end = p_im2 + src2->imageSize; //4 Channels (Include Alpha)
 
	nChan_im1 = src1->nChannels;
	nChan_dst = dst->nChannels;
 
 
	//loop by 2 pixels
	while(p_im2<end)
	{
 
		//Compute the ratio for this pixel.
		ratio=(float)(p_im2[3]/255.f);
 
		//Chan 0
		c=0;
		tmp=((float)(p_im1[c]))*(1-ratio) + ((float)(p_im2[c]))*(ratio);
		p_dst[c]=(uint8_t)(tmp+0.5f);
 
		//Chan 1
		c=1;
		tmp=((float)(p_im1[c]))*(1-ratio) + ((float)(p_im2[c]))*(ratio);
		p_dst[c]=(uint8_t)(tmp+0.5f);
 
		//Chan 2
		c=2;
		tmp=((float)(p_im1[c]))*(1-ratio) + ((float)(p_im2[c]))*(ratio);
		p_dst[c]=(uint8_t)(tmp+0.5f);
 
		//Chan Alpha
		if(nChan_dst==4)
		{
			if(nChan_im1!=4) p_dst[3]=255;
			else 		p_dst[3]=p_im1[3];
		}
 
 
		//Jump to next pixel
		p_im1+=nChan_im1;
		p_im2+=4;
		p_dst+=nChan_dst;
	}
}