UIImage与RGBA、BGR、GrayScale
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0.0762017.04.12 11:09:38字数 277阅读 1,916
格式类型：
RBGA - 包含Alpha通道
RGB
BGR
Gray - 灰度图
首先理解一张图片的组成，每张图片都是由无数个有序排列的带有颜色的像素点（Pixel）组成的，这些Pixel的排列都可以理解为一个二维数组，每个Pixel都是一个颜色点，即包含RGBA的Pixel。
什么是RGBA呢
R - Red
G - Green
B - Blue
A - Alpha 透明度
1、将UIImage转为RGBA格式
-(unsignedchar*)getRGBAWithImage:(UIImage*)image{intRGBA=4;CGImageRef imageRef=[image CGImage];size_t width=CGImageGetWidth(imageRef);size_t height=CGImageGetHeight(imageRef);CGColorSpaceRef colorSpace=CGColorSpaceCreateDeviceRGB();unsignedchar*rawData=(unsignedchar*)malloc(width*height*sizeof(unsignedchar)*RGBA);NSUInteger bytesPerPixel=RGBA;NSUInteger bytesPerRow=bytesPerPixel*width;NSUInteger bitsPerComponent=8;CGContextRef context=CGBitmapContextCreate(rawData,width,height,bitsPerComponent,bytesPerRow,colorSpace,kCGImageAlphaPremultipliedLast|kCGBitmapByteOrder32Big);CGContextDrawImage(context,CGRectMake(0,0,width,height),imageRef);CGColorSpaceRelease(colorSpace);CGContextRelease(context);returnrawData;}
继续上面的工作，获取这张图片中某个Pixel的RGBA值
-(void)getRGBAFromImage:(UIImage*)image atX:(int)xx andY:(int)yy{intRGBA=4;CGImageRef imageRef=[image CGImage];size_t width=CGImageGetWidth(imageRef);size_t height=CGImageGetHeight(imageRef);// 从image的data buffer中取得影像，放入格式化后的rawData中CGColorSpaceRef colorSpace=CGColorSpaceCreateDeviceRGB();unsignedchar*rawData=(unsignedchar*)malloc(height*width*RGBA);NSUInteger bytesPerPixel=RGBA;NSUInteger bytesPerRow=bytesPerPixel*width;NSUInteger bitsPerComponent=8;CGContextRef context=CGBitmapContextCreate(rawData,width,height,bitsPerComponent,bytesPerRow,colorSpace,kCGImageAlphaPremultipliedLast|kCGBitmapByteOrder32Big);CGColorSpaceRelease(colorSpace);// 清空CGContextRef再绘制CGContextClearRect(context,CGRectMake(0.0,0.0,width,height));CGContextDrawImage(context,CGRectMake(0,0,width,height),imageRef);CGContextRelease(context);// 将XY坐标转成一维数组unsignedlongbyteIndex=(bytesPerRow*yy)+(bytesPerPixel*xx);// 取得RGBA位的数据CGFloat red=rawData[byteIndex];CGFloat green=rawData[byteIndex+1];CGFloat blue=rawData[byteIndex+2];CGFloat alpha=rawData[byteIndex+3];// 利用RGB计算灰阶的亮度值CGFloat gray=(red+green+blue)/3;// 输出NSLog(@"%@",[NSString stringWithFormat:@"%.2f",red]);NSLog(@"%@",[NSString stringWithFormat:@"%.2f",green]);NSLog(@"%@",[NSString stringWithFormat:@"%.2f",blue]);NSLog(@"%@",[NSString stringWithFormat:@"%.2f",alpha]);NSLog(@"%@",[NSString stringWithFormat:@"%.2f",gray]);free(rawData);}
2、将图片转为BGR格式
转换为BGR格式，顾名思义，BGR与RGBA，我们只需要把RGBA数据取到，去掉Alpha，再调换一下RGB的顺序就可以了，下面是具体调换代码：
-(unsignedchar*)getBGRWithImage:(UIImage*)image{intRGBA=4;intRGB=3;CGImageRef imageRef=[image CGImage];size_t width=CGImageGetWidth(imageRef);size_t height=CGImageGetHeight(imageRef);CGColorSpaceRef colorSpace=CGColorSpaceCreateDeviceRGB();unsignedchar*rawData=(unsignedchar*)malloc(width*height*sizeof(unsignedchar)*RGBA);NSUInteger bytesPerPixel=RGBA;NSUInteger bytesPerRow=bytesPerPixel*width;NSUInteger bitsPerComponent=8;CGContextRef context=CGBitmapContextCreate(rawData,width,height,bitsPerComponent,bytesPerRow,colorSpace,kCGImageAlphaPremultipliedLast|kCGBitmapByteOrder32Big);CGContextDrawImage(context,CGRectMake(0,0,width,height),imageRef);CGColorSpaceRelease(colorSpace);CGContextRelease(context);unsignedchar*tempRawData=(unsignedchar*)malloc(width*height*3*sizeof(unsignedchar));for(inti=0;i 什么是Gray灰度? 灰度（Gray scale）数字图像是每个像素只有一个采样颜色的图像。这类图像通常显示为从最暗黑色到最亮的白色的灰度 1、将一张图片转为灰度图 -(unsignedchar*)getGrayWithImage:(UIImage*)image{intGRAY=1;// 获取灰度图CGImageRef imageRef=[image CGImage];intwidth=image.size.width;intheight=image.size.height;unsignedchar*rawData=(unsignedchar*)malloc(width*height*sizeof(unsignedchar));CGColorSpaceRef colorSpace=CGColorSpaceCreateDeviceGray();NSUInteger bytesPerPixel=GRAY;NSUInteger bytesPerRow=bytesPerPixel*width;NSUInteger bitsPerComponent=8;CGContextRef context=CGBitmapContextCreate(rawData,width,height,bitsPerComponent,bytesPerRow,colorSpace,0);CGContextDrawImage(context,CGRectMake(0,0,width,height),imageRef);CGColorSpaceRelease(colorSpace);CGContextRelease(context);returnrawData;} 参考资料 彩笔的笔记本