作者：gnuhpc
出处：http://www.cnblogs.com/gnuhpc/
1.RGBA色彩空间基本知识：
RGBA stands for R ed G reen B lue A lpha.
While it is sometimes described as a color space, it is actually simply
a use of the RGB color model, with extra information. The color is RGB , and may belong to any RGB color space, but an integral alpha value as invented by Catmull and Smith between 1971 and 1972 enables alpha blending and alpha compositing . The inventors named alpha after the Greek letter in the classic linear interpolation formula αA + (1-α)B.
The alpha channel is normally used as an opacity channel. If a pixel has a value of 0% in its alpha channel, it is fullytransparent
(and, thus, invisible), whereas a value of 100% in the alpha channel
gives a fully opaque pixel (traditional digital images). Values between
0% and 100% make it possible for pixels to show through a background
like a glass (translucency), an effect not possible with simple binary
(transparent or opaque) transparency. It allows easy image compositing . Alpha channel values can be expressed as a percentage, integer, or real number between 0 and 1 like RGB parameters.
Sometimes this is referred as ARGB (like RGBA, but first datum is alpha), which is used, for example, in Macromedia
products terminology. For example, 0x80FFFF00 is 50%-transparent
yellow, because all parameters are expressed on a 0-to-255 scale. 0x80
is 128, approximately half 255 (alpha 50%); 0xFF is 255, the greatest
value a parameter can have (pure red); the second 0xFF is like the
previous, but for green; and 0x00 is 0 in decimal (no blue). Red,
green, and half transparency mixture are 50% transparent yellow.
PNG is an image format that uses RGBA.
说白了就是一个像素透明度的位。
2.实例：
#include <iostream>
#include <cv.h>
#include <highgui.h>
char *filename="sample.png";
IplImage *cvLoadImageBGRA(const char *filename,int iscolor = 1);
IplImage *GetMaskFromBGR(IplImage *BGRImg); //取得图像掩码
int main(int argc, char **argv)
{
IplImage *imgBGRA = cvLoadImageBGRA(filename,CV_LOAD_IMAGE_ANYDEPTH | CV_LOAD_IMAGE_ANYCOLOR);
if(imgBGRA == NULL )
{
std::cerr << "Can't Load Image/n";
return -1;
}
cvNamedWindow("RGBA",CV_WINDOW_AUTOSIZE);
cvShowImage("RGBA",imgBGRA);
cvReleaseImage( & imgBGRA);
cvWaitKey(0);
cvDestroyAllWindows();
return EXIT_SUCCESS;
}
IplImage *cvLoadImageBGRA(const char *filename,int iscolor)
{
//RGB
IplImage *ImgBGR = cvLoadImage(filename,iscolor);
if(ImgBGR == NULL)
{
return NULL;
}
//创建图像掩码
IplImage *Mask = GetMaskFromBGR(ImgBGR);
if(Mask == NULL)
{
cvReleaseImage(&ImgBGR);
return NULL;
}
IplImage *BGRA = cvCreateImage(cvGetSize(ImgBGR),IPL_DEPTH_8U,4);
if(BGRA == NULL)
{
cvReleaseImage(&ImgBGR);
cvReleaseImage(&Mask);
return NULL;
}
const CvArr *InputPlane[2]={ImgBGR,Mask};
int from_to[] = { 0, 2, 1, 1, 2, 0, 3, 3 };//设定对应的BGRA
cvMixChannels(InputPlane,2,(CvArr**)&BGRA,1,from_to,4);
cvReleaseImage(&Mask);
cvReleaseImage(&ImgBGR);
return BGRA;
}
IplImage *GetMaskFromBGR(IplImage *BGRImg)
{
//灰度单通道
IplImage *gray = cvCreateImage(cvGetSize(BGRImg),IPL_DEPTH_8U,1);
if(gray == NULL){return NULL;}
//创建灰度图像
cvCvtColor(BGRImg, gray, CV_BGR2GRAY);
//创建图像掩码
cvThreshold(gray,gray,254,255,CV_THRESH_BINARY);
cvNot(gray,gray);
return gray;
}
作者：gnuhpc
出处：http://www.cnblogs.com/gnuhpc/
作者：gnuhpc
出处：http://www.cnblogs.com/gnuhpc/
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