获取图片每（某）个像素点的RBGA值

最近项目有个需求，获取调色板上某个点的RBGA值，来设置背景颜色。查找了一些资料，经过多次测试，最终拿到的RGBA值基本一致（这里为什么说基本一致呢，如果RGBA值的取值范围在0～255之间的话，结果会有1-2个点的误差）。方法如下：

获取图片上某个点的RGBA值

//获取图片某个点的RGBA值
- (NSMutableArray *)getImagePixel:(UIImage *)image point:(CGPoint)aPoint {

NSMutableArray *byteArray = [[NSMutableArray alloc] initWithCapacity:10];
CGImageRef cgimage = image.CGImage;
size_t scale = CGImageGetWidth(cgimage) / image.size.width;

size_t bpr = CGImageGetBytesPerRow(cgimage);             //每行的字节数
size_t bpp = CGImageGetBitsPerPixel(cgimage);            //每个像素的位数
size_t bpc = CGImageGetBitsPerComponent(cgimage);        //每个字节的组成部分
size_t bytes_per_pixel = bpp / bpc;

// Get CGDataProviderRef from cgimage
CGDataProviderRef provider = CGImageGetDataProvider(cgimage);

@autoreleasepool
{
//Using (__bridge_transfer NSData *) casts the provider to type NSData and gives ownership to ARC, but still not discarded
NSData *data = (__bridge_transfer NSData *)CGDataProviderCopyData(provider);

const UInt8 *bytes = (Byte *)[data bytes];

size_t row = aPoint.y*scale;
size_t col = aPoint.x*scale;

const UInt8* pixel = &bytes[row * bpr + col * bytes_per_pixel];

for(unsigned short i = 0; i < 4; i+=4) {

unsigned short red = pixel[i];                  // red channel - unused
unsigned short green = pixel[i+1];              // green channel
unsigned short blue = pixel[i+2];               // blue channel
unsigned short alpha = pixel[i+3];              // alpha channel - unused

[byteArray addObject:@(red)];
[byteArray addObject:@(green)];
[byteArray addObject:@(blue)];
[byteArray addObject:@(alpha)];
}
data = nil;
}
return byteArray;
}

获取图片每个像素点的RGBA值
//获取图片每个像素点的RGBA值
- (NSMutableArray *)getImagePixel:(UIImage *)image point:(CGPoint)aPoint {

// Create array to add all files into total image
NSMutableArray *byteArray = [[NSMutableArray alloc] initWithCapacity:(image.size.width * image.size.height)];

CGImageRef cgimage = image.CGImage;

size_t width = CGImageGetWidth(cgimage);
size_t height = CGImageGetHeight(cgimage);

size_t bpr = CGImageGetBytesPerRow(cgimage); //每行的字节数
size_t bpp = CGImageGetBitsPerPixel(cgimage); //每个像素的位数
size_t bpc = CGImageGetBitsPerComponent(cgimage); //每个字节的组成部分
size_t bytes_per_pixel = bpp / bpc;

// Get CGDataProviderRef from cgimage
CGDataProviderRef provider = CGImageGetDataProvider(cgimage);

@autoreleasepool
{
//Using (__bridge_transfer NSData *) casts the provider to type NSData and gives ownership to ARC, but still not discarded
NSData *data = (__bridge_transfer NSData *)CGDataProviderCopyData(provider);

const UInt8 *bytes = (Byte *)[data bytes];

// Populate byte array with channel data from each pixel
for(size_t row = 0; row < height; row++) {

for(size_t col = 0; col < width; col++) {

const UInt8* pixel = &bytes[row * bpr + col * bytes_per_pixel];
for(unsigned short i = 0; i < 4; i+=4) {

unsigned short red = pixel[i]; // red channel
unsigned short green = pixel[i+1]; // green channel
unsigned short blue = pixel[i+2]; // blue channel
unsigned short alpha = pixel[i+3]; // alpha channel

[byteArray addObject:@(red)];
[byteArray addObject:@(green)];
[byteArray addObject:@(blue)];
[byteArray addObject:@(alpha)];
}
}
}
data = nil;
}
return byteArray;
}