C++ 在未填充到4字节的3通道上进行图像重采样?
我发现了一种图像重采样算法,在缩小尺寸时可以产生非常好的图像。它适用于3通道图像,每像素填充4字节。对于一个没有填充到每个通道4字节的图像,我应该做些什么更改才能使其正常工作?像jpeg图像。目标映像是4字节填充的。另外,你会给这个算法取什么名字 最初在这里发现: 简化代码:C++ 在未填充到4字节的3通道上进行图像重采样?,c++,image,algorithm,visual-studio,image-resizing,C++,Image,Algorithm,Visual Studio,Image Resizing,我发现了一种图像重采样算法,在缩小尺寸时可以产生非常好的图像。它适用于3通道图像,每像素填充4字节。对于一个没有填充到每个通道4字节的图像,我应该做些什么更改才能使其正常工作?像jpeg图像。目标映像是4字节填充的。另外,你会给这个算法取什么名字 最初在这里发现: 简化代码: void Resize_HQ(unsigned char* src, int w1, int h1, unsigned char* dest, int w2, int h2) { // arbitrary resi
void Resize_HQ(unsigned char* src, int w1, int h1, unsigned char* dest, int w2, int h2)
{
// arbitrary resize.
unsigned int *dsrc = (unsigned int *)src;
unsigned int *ddest = (unsigned int *)dest;
bool bUpsampleX = (w1 < w2);
bool bUpsampleY = (h1 < h2);
// If too many input pixels map to one output pixel, our 32-bit accumulation values
// could overflow - so, if we have huge mappings like that, cut down the weights:
// 256 max color value
// *256 weight_x
// *256 weight_y
// *256 (16*16) maximum # of input pixels (x,y) - unless we cut the weights down...
int weight_shift = 0;
float source_texels_per_out_pixel = ( (w1/(float)w2 + 1)
* (h1/(float)h2 + 1)
);
float weight_per_pixel = source_texels_per_out_pixel * 256 * 256; //weight_x * weight_y
float accum_per_pixel = weight_per_pixel*256; //color value is 0-255
float weight_div = accum_per_pixel / 4294967000.0f;
if (weight_div > 1)
weight_shift = (int)ceilf( logf((float)weight_div)/logf(2.0f) );
weight_shift = min(15, weight_shift); // this could go to 15 and still be ok.
float fh = 256*h1/(float)h2;
float fw = 256*w1/(float)w2;
// FOR EVERY OUTPUT PIXEL
for (int y2=0; y2<h2; y2++)
{
// find the y-range of input pixels that will contribute:
int y1a = (int)((y2 )*fh);
int y1b = (int)((y2+1)*fh);
if (bUpsampleY) // map to same pixel -> we want to interpolate between two pixels!
y1b = y1a + 256;
y1b = min(y1b, 256*h1 - 1);
int y1c = y1a >> 8;
int y1d = y1b >> 8;
for (int x2=0; x2<w2; x2++)
{
// find the x-range of input pixels that will contribute:
int x1a = (int)((x2 )*fw);
int x1b = (int)((x2+1)*fw);
if (bUpsampleX) // map to same pixel -> we want to interpolate between two pixels!
x1b = x1a + 256;
x1b = min(x1b, 256*w1 - 1);
int x1c = x1a >> 8;
int x1d = x1b >> 8;
// ADD UP ALL INPUT PIXELS CONTRIBUTING TO THIS OUTPUT PIXEL:
unsigned int r=0, g=0, b=0, a=0;
for (int y=y1c; y<=y1d; y++)
{
unsigned int weight_y = 256;
if (y1c != y1d)
{
if (y==y1c)
weight_y = 256 - (y1a & 0xFF);
else if (y==y1d)
weight_y = (y1b & 0xFF);
}
unsigned int *dsrc2 = &dsrc[y*w1 + x1c];
for (int x=x1c; x<=x1d; x++)
{
unsigned int weight_x = 256;
if (x1c != x1d)
{
if (x==x1c)
weight_x = 256 - (x1a & 0xFF);
else if (x==x1d)
weight_x = (x1b & 0xFF);
}
unsigned int c = *dsrc2++;//dsrc[y*w1 + x];
unsigned int r_src = (c ) & 0xFF;
unsigned int g_src = (c>> 8) & 0xFF;
unsigned int b_src = (c>>16) & 0xFF;
unsigned int w = (weight_x * weight_y) >> weight_shift;
r += r_src * w;
g += g_src * w;
b += b_src * w;
a += w;
}
}
// write results
unsigned int c = ((r/a)) | ((g/a)<<8) | ((b/a)<<16);
*ddest++ = c;//ddest[y2*w2 + x2] = c;
}
}
}
致:
以及:
致:
还是没用…:| 原始代码使用3个字节作为颜色,1个字节作为alpha或padding,每个像素使用4个字节。它读取32位整数,并屏蔽颜色。您没有第4个字节,因此需要将内容更改为从无符号字符读取 将
dsrc
和ddest
更改为无符号字符*
。然后,dsrc2
的声明变为
unsigned char *dsrc2 = &dsrc[(y*w1 + x1c) * 3];
扔掉无符号int c
(两个位置)。将r\u src
等替换为
unsigned int r_src = *dsrc2++;
unsigned int g_src = *dsrc2++;
unsigned int b_src = *dsrc2++;
每次写入结果也必须是一个字节
*ddest++ = unsigned char(r / a);
*ddest++ = unsigned char(g / a);
*ddest++ = unsigned char(b / a);
我认为您输入了一个错误,dsrc2也应该声明为unsigned char*。这样做之后,你的配方就起作用了。谢谢
unsigned int c = *(unsigned int *)dsrc2;
dsrc2 += 3;
unsigned char *dsrc2 = &dsrc[(y*w1 + x1c) * 3];
unsigned int r_src = *dsrc2++;
unsigned int g_src = *dsrc2++;
unsigned int b_src = *dsrc2++;
*ddest++ = unsigned char(r / a);
*ddest++ = unsigned char(g / a);
*ddest++ = unsigned char(b / a);