[英]How to get pixel color at location from UIimage scaled within a UIimageView
I'm currently using this technique to get the color of a pixel in a UIimage. 我目前正在使用这种技术来获取UIimage中像素的颜色。 (on Ios)
(在Ios上)
- (UIColor*) getPixelColorAtLocation:(CGPoint)point {
UIColor* color = nil;
CGImageRef inImage = self.image.CGImage;
// Create off screen bitmap context to draw the image into. Format ARGB is 4 bytes for each pixel: Alpa, Red, Green, Blue
CGContextRef cgctx = [self createARGBBitmapContextFromImage:inImage];
if (cgctx == NULL) { return nil; /* error */ }
size_t w = CGImageGetWidth(inImage);
size_t h = CGImageGetHeight(inImage);
CGRect rect = {{0,0},{w,h}};
// Draw the image to the bitmap context. Once we draw, the memory
// allocated for the context for rendering will then contain the
// raw image data in the specified color space.
CGContextDrawImage(cgctx, rect, inImage);
// Now we can get a pointer to the image data associated with the bitmap
// context.
unsigned char* data = CGBitmapContextGetData (cgctx);
if (data != NULL) {
//offset locates the pixel in the data from x,y.
//4 for 4 bytes of data per pixel, w is width of one row of data.
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];
NSLog(@"offset: %i colors: RGB A %i %i %i %i",offset,red,green,blue,alpha);
color = [UIColor colorWithRed:(red/255.0f) green:(green/255.0f) blue:(blue/255.0f) alpha:(alpha/255.0f)];
}
// When finished, release the context
CGContextRelease(cgctx);
// Free image data memory for the context
if (data) { free(data); }
return color;
} }
As illustrated here; 如此处所示;
http://www.markj.net/iphone-uiimage-pixel-color/ http://www.markj.net/iphone-uiimage-pixel-color/
it works quite well, but when working with images larger than the UIImageView it fails. 它工作得很好,但是在处理大于UIImageView的图像时会失败。 I tried adding an image and changing the scaling mode to fit the view.
我尝试添加图像并更改缩放模式以适合视图。 How would I modify the code to so that it would still be able to sample the pixel color with a scaled image.
我如何将代码修改为,以便仍然能够使用缩放图像对像素颜色进行采样。
try this for swift3 试试这个swift3
func getPixelColor(image: UIImage, x: Int, y: Int, width: CGFloat) -> UIColor
{
let pixelData = CGDataProviderCopyData(CGImageGetDataProvider(image.CGImage))
let data: UnsafePointer<UInt8> = CFDataGetBytePtr(pixelData)
let pixelInfo: Int = ((Int(width) * y) + x) * 4
let r = CGFloat(data[pixelInfo]) / CGFloat(255.0)
let g = CGFloat(data[pixelInfo+1]) / CGFloat(255.0)
let b = CGFloat(data[pixelInfo+2]) / CGFloat(255.0)
let a = CGFloat(data[pixelInfo+3]) / CGFloat(255.0)
return UIColor(red: r, green: g, blue: b, alpha: a)
}
Here's a pointer: 这是一个指针:
0x3A28213A //sorry, I couldn't resist the joke
For real now: after going through the comments on the page at markj.net, a certain James has suggested to make the following changes: 现在来看:在浏览markj.net页面上的评论后,某位James建议进行以下更改:
size_t w = CGImageGetWidth(inImage); //Written by Mark
size_t h = CGImageGetHeight(inImage); //Written by Mark
float xscale = w / self.frame.size.width;
float yscale = h / self.frame.size.height;
point.x = point.x * xscale;
point.y = point.y * yscale;
(thanks to http://www.markj.net/iphone-uiimage-pixel-color/comment-page-1/#comment-2159 ) (感谢http://www.markj.net/iphone-uiimage-pixel-color/comment-page-1/#comment-2159 )
This didn't actually work for me... Not that I did much testing, and I'm not the world's greatest programmer (yet)... 这实际上对我没有用……不是我做了很多测试,而且我不是世界上最伟大的程序员(至今)……
My solution was to scale the UIImageView
in such a way that each pixel of the image in it was the same size as a standard CGPoint on the screen, then I took my color like normal (using getPixelColorAtLocation:(CGPoint)point
) , then I scaled the image back to the size I wanted. 我的解决方案是以某种方式缩放
UIImageView
,以使其图像中的每个像素与屏幕上的标准CGPoint大小相同,然后像正常一样使用我的颜色(使用getPixelColorAtLocation:(CGPoint)point
),然后将图像缩放回我想要的大小。
Hope this helps! 希望这可以帮助!
Use the UIImageView Layer: 使用UIImageView层:
- (UIColor*) getPixelColorAtLocation:(CGPoint)point {
UIColor* color = nil;
UIGraphicsBeginImageContext(self.frame.size);
CGContextRef cgctx = UIGraphicsGetCurrentContext();
if (cgctx == NULL) { return nil; /* error */ }
[self.layer renderInContext:cgctx];
unsigned char* data = CGBitmapContextGetData (cgctx);
/*
...
*/
UIGraphicsEndImageContext();
return color;
}
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