How to get the pixel color on touch?
I know this is a common question and there are a lot of answers of this question. I've used some of this. Although many of them are the same. But the sad thing for me is that none of them worked for me. The following codes i've used till now.
-(void)getRGBAsFromImage:(UIImage*)image atX:(int)xx andY:(int)yy
{
// First get the image into your data buffer
CGImageRef imageRef = [image CGImage];
NSUInteger width = CGImageGetWidth(imageRef);
NSUInteger height = CGImageGetHeight(imageRef);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *rawData = (unsigned char*) calloc(height * width * 4, sizeof(unsigned char));
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(rawData, width, height,
bitsPerComponent, bytesPerRow, colorSpace,
kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);
CGContextRelease(context);
// Now your rawData contains the image data in the RGBA8888 pixel format.
int byteIndex = (bytesPerRow * yy) + xx * bytesPerPixel;
CGFloat red = (rawData[byteIndex] * 1.0) / 255.0;
CGFloat green = (rawData[byteIndex + 1] * 1.0) / 255.0;
CGFloat blue = (rawData[byteIndex + 2] * 1.0) / 255.0;
CGFloat alpha = (rawData[byteIndex + 3] * 1.0) / 255.0;
byteIndex += 4;
NSLog(@"the vale of the rbg of red is %f",red);
demoColor.tintColor = [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
free(rawData);
}
Here is another approach i've used -
- (CGContextRef) createARGBBitmapContextFromImage:(CGImageRef) inImage {
CGContextRef context = NULL;
CGColorSpaceRef colorSpace;
void * bitmapData;
int bitmapByteCount;
int bitmapBytesPerRow;
// Get image width, height. We'll use the entire image.
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 = (pixelsWide * 4);
bitmapByteCount = (bitmapBytesPerRow * pixelsHigh);
// Use the generic RGB color space.
//colorSpace = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB);
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;
}
- (UIColor*) getPixelColorAtLocation:(CGPoint)point {
UIColor* color = nil;
//CGImageRef inImage = self.image.CGImage;
CGImageRef inImage = [AppDelegate getInstance].capturedImage.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;
}
But none of these has been worked for me. Please help me out to work with this. Is there anything i'm missing ?
I have 2 UIImageView in my UI. The one which is in back contains the image from which i need to pick the color of a pixel that is touched. And the other UIImageView is to paint over the back image with the picked color.
Please help. Any help will be very much appreciated.
This is the one I've used, and it looks simpler than the methods you've tried.
In my custom view class, I have this:
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [[event allTouches] anyObject];
CGPoint loc = [touch locationInView:self];
self.pickedColor = [self colorOfPoint:loc];
}
colorOfPoint is a method in a category on UIView, with this code:
#import "UIView+ColorOfPoint.h"
#import <QuartzCore/QuartzCore.h>
@implementation UIView (ColorOfPoint)
-(UIColor *) colorOfPoint:(CGPoint)point
{
unsigned char pixel[4] = {0};
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(pixel,
1, 1, 8, 4, colorSpace, (CGBitmapInfo)kCGImageAlphaPremultipliedLast);
CGContextTranslateCTM(context, -point.x, -point.y);
[self.layer renderInContext:context];
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
UIColor *color = [UIColor colorWithRed:pixel[0]/255.0
green:pixel[1]/255.0 blue:pixel[2]/255.0
alpha:pixel[3]/255.0];
return color;
}
Don't forget to import the category into the custom view class and add the QuartzCore framework.
Trivial note for 2013: cast that last argument as (CGBitmapInfo) to avoid an implicit conversion warning: example here. Hope it helps.
Swift 4, Xcode 9 - With a UIImageView Extension
This is a combination of all of the answers above but in an extension
extension UIImageView {
func getPixelColorAt(point:CGPoint) -> UIColor{
let pixel = UnsafeMutablePointer<CUnsignedChar>.allocate(capacity: 4)
let colorSpace = CGColorSpaceCreateDeviceRGB()
let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue)
let context = CGContext(data: pixel, width: 1, height: 1, bitsPerComponent: 8, bytesPerRow: 4, space: colorSpace, bitmapInfo: bitmapInfo.rawValue)
context!.translateBy(x: -point.x, y: -point.y)
layer.render(in: context!)
let color:UIColor = UIColor(red: CGFloat(pixel[0])/255.0,
green: CGFloat(pixel[1])/255.0,
blue: CGFloat(pixel[2])/255.0,
alpha: CGFloat(pixel[3])/255.0)
pixel.deallocate(capacity: 4)
return color
}
}
How to use
override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
let touch = touches.first
if let point = touch?.location(in: view) {
let color = myUIImageView.getPixelColorAt(point: point)
print(color)
}
}
Thank you for @Aggressor's post the code above
Swift 2.1
func getPixelColorAtPoint(point:CGPoint) -> UIColor{
let pixel = UnsafeMutablePointer<CUnsignedChar>.alloc(4)
let colorSpace = CGColorSpaceCreateDeviceRGB()
let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.PremultipliedLast.rawValue)
let context = CGBitmapContextCreate(pixel, 1, 1, 8, 4, colorSpace, bitmapInfo.rawValue)
CGContextTranslateCTM(context, -point.x, -point.y)
view.layer.renderInContext(context!)
let color:UIColor = UIColor(red: CGFloat(pixel[0])/255.0, green: CGFloat(pixel[1])/255.0, blue: CGFloat(pixel[2])/255.0, alpha: CGFloat(pixel[3])/255.0)
pixel.dealloc(4)
return color
}
Swift 3, Xcode Version 8.2 (8C38) and Swift 4, Xcode Version 9.1 (9B55)
func getPixelColorAtPoint(point:CGPoint, sourceView: UIView) -> UIColor{
let pixel = UnsafeMutablePointer<CUnsignedChar>.allocate(capacity: 4)
let colorSpace = CGColorSpaceCreateDeviceRGB()
let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue)
let context = CGContext(data: pixel, width: 1, height: 1, bitsPerComponent: 8, bytesPerRow: 4, space: colorSpace, bitmapInfo: bitmapInfo.rawValue)
var color: UIColor? = nil
if let context = context {
context.translateBy(x: -point.x, y: -point.y)
sourceView.layer.render(in: context)
color = UIColor(red: CGFloat(pixel[0])/255.0,
green: CGFloat(pixel[1])/255.0,
blue: CGFloat(pixel[2])/255.0,
alpha: CGFloat(pixel[3])/255.0)
pixel.deallocate(capacity: 4)
}
return color
}
Great answer rdelmar this helped me A LOT!
Here is how I did the above in Swift:
override func touchesBegan(touches: NSSet, withEvent event: UIEvent)
{
var touch:UITouch = event.allTouches()!.anyObject() as UITouch
var loc = touch.locationInView(self)
var color:UIColor = getPixelColorAtPoint(loc)
println(color)
}
//returns the color data of the pixel at the currently selected point
func getPixelColorAtPoint(point:CGPoint)->UIColor
{
let pixel = UnsafeMutablePointer<CUnsignedChar>.alloc(4)
var colorSpace = CGColorSpaceCreateDeviceRGB()
let bitmapInfo = CGBitmapInfo(CGImageAlphaInfo.PremultipliedLast.rawValue)
let context = CGBitmapContextCreate(pixel, 1, 1, 8, 4, colorSpace, bitmapInfo)
CGContextTranslateCTM(context, -point.x, -point.y)
layer.renderInContext(context)
var color:UIColor = UIColor(red: CGFloat(pixel[0])/255.0, green: CGFloat(pixel[1])/255.0, blue: CGFloat(pixel[2])/255.0, alpha: CGFloat(pixel[3])/255.0)
pixel.dealloc(4)
return color
}
First, I'd like to thank the author of this code, it helped me a lot for my game project, as I was looking for this function to do a pixel-perfect hitbox (excluding where the aplha is O). Here's a little update for Swift 5:
// Fonction permettant de retourner les valeurs RGBA d'un pixel d'une vue
func getPixelColor(atPosition:CGPoint) -> UIColor{
var pixel:[CUnsignedChar] = [0, 0, 0, 0];
let colorSpace = CGColorSpaceCreateDeviceRGB();
let bitmapInfo = CGBitmapInfo(rawValue: CGImageAlphaInfo.premultipliedLast.rawValue);
let context = CGContext(data: &pixel, width: 1, height: 1, bitsPerComponent: 8, bytesPerRow: 4, space: colorSpace, bitmapInfo: bitmapInfo.rawValue);
context!.translateBy(x: -atPosition.x, y: -atPosition.y);
layer.render(in: context!);
let color:UIColor = UIColor(red: CGFloat(pixel[0])/255.0,
green: CGFloat(pixel[1])/255.0,
blue: CGFloat(pixel[2])/255.0,
alpha: CGFloat(pixel[3])/255.0);
return color;
}
I had somme issues with pixel.dealloc(4), as in Swift 5 it seems that you can't dealloc with capacity parameter anymore. I removed the (4), but it had some weird behavior (as the dealloc() didn't dealloc the whole array).
I didn't do an extension of UIView as in my project I have my own subclass, but this can be easily done.
The way I implement the code:
// Méthode déterminant si le "touch" est validé par l'objet (par défaut, exclut les zones transparentes et les objets invisibles). A surcharger si nécessaire.
func isHit(atPosition position:CGPoint) -> Bool
{
// Si l'objet n'est pas caché (paramètre isHidden) et si la zone touchée correspond à une zone effectivement dessinée (non transparente), retourne true.
if (!self.isHidden && self.getPixelColor(atPosition: position).cgColor.alpha != 0) {return true}
else {return false}
}
I hope this can help.