UIImage_Category

获取图片上一点的颜色

根据图片上的一点，获得对应的颜色值。

UIImage *image = [UIImage imageNamed:@"sns_icon_15"];
UIColor *color = [self getColorAtPoint:CGPointMake(4, 44) atImage:image];

实现代码：

- (UIColor*) getColorAtPoint:(CGPoint)point atImage:(UIImage *)image {

UIColor* color = nil;
CGImageRef cgImage = image.CGImage;
CGContextRef context = [self createARGBBitmapContextFromImage:cgImage];

if (context == NULL) {
return nil;
}
size_t w = CGImageGetWidth(cgImage);
size_t h = CGImageGetHeight(cgImage);
CGRect rect = {{0,0},{w,h}};

CGContextDrawImage(context, rect, cgImage);
unsigned char* data = CGBitmapContextGetData (context);
if (data != NULL) {
int offset = 4*((w*round(point.y))+round(point.x));
int alpha =  data[offset];
int red = data[offset+1];
int green = data[offset+2];
int blue = data[offset+3];
color = [UIColor colorWithRed:(red/255.0f) green:(green/255.0f) blue:
(blue/255.0f) alpha:(alpha/255.0f)];
}
CGContextRelease(context);
if (data) {
free(data);
}
return color;
}

- (CGContextRef)createARGBBitmapContextFromImage:(CGImageRef)inImage {
CGContextRef context = NULL;
CGColorSpaceRef colorSpace;
void *bitmapData;
int bitmapByteCount;
int bitmapBytesPerRow;

size_t pixelsWide = CGImageGetWidth(inImage);
size_t pixelsHigh = CGImageGetHeight(inImage);

// Declare the number of bytes per row. Each pixel in the bitmap in this
// example is represented by 4 bytes; 8 bits each of red, green, blue, and
// alpha.
bitmapBytesPerRow   = ((int)pixelsWide * 4);
bitmapByteCount     = (bitmapBytesPerRow * (int)pixelsHigh);

// Use the generic RGB color space.
colorSpace = CGColorSpaceCreateDeviceRGB();

if (colorSpace == NULL)
{
fprintf(stderr,"Error allocating color space\n");
return NULL;
}

// Allocate memory for image data. This is the destination in memory
// where any drawing to the bitmap context will be rendered.
bitmapData = malloc(bitmapByteCount);
if (bitmapData == NULL)
{
fprintf(stderr,"Memory not allocated!");
CGColorSpaceRelease(colorSpace);
return NULL;
}

// Create the bitmap context. We want pre-multiplied ARGB, 8-bits
// per component. Regardless of what the source image format is
// (CMYK, Grayscale, and so on) it will be converted over to the format
// specified here by CGBitmapContextCreate.
context = CGBitmapContextCreate(bitmapData,
pixelsWide,
pixelsHigh,
8,   // bits per component
bitmapBytesPerRow,
colorSpace,
kCGImageAlphaPremultipliedFirst);
if (context == NULL)
{
free(bitmapData);
fprintf(stderr,"Context not created!");
}

// Make sure and release colorspace before returning
CGColorSpaceRelease(colorSpace);

return context;
}

获得纯色image

(UIImage )imageWithColor:(UIColor )color size:(CGSize)size {

CGRect rect = CGRectMake(0.0f, 0.0f, size.width, size.height);

UIGraphicsBeginImageContext(rect.size);

CGContextRef context = UIGraphicsGetCurrentContext();

CGContextSetFillColorWithColor(context, [color CGColor]);

CGContextFillRect(context, rect);

UIImage *image = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

return image;

}