问题
How can I get the RGB value of a particular pixel in a UIImage?
回答1:
You can't access the raw data directly, but by getting the CGImage of this image you can access it. here is a link to another question that answers your question and others you might have regarding detailed image manipulation : CGImage
回答2:
Try this very simple code:
I used to detect a wall in my maze game (the only info that I need is the alpha channel, but I included the code to get the other colors for you):
- (BOOL)isWallPixel:(UIImage *)image xCoordinate:(int)x yCoordinate:(int)y {
CFDataRef pixelData = CGDataProviderCopyData(CGImageGetDataProvider(image.CGImage));
const UInt8* data = CFDataGetBytePtr(pixelData);
int pixelInfo = ((image.size.width * y) + x ) * 4; // The image is png
//UInt8 red = data[pixelInfo]; // If you need this info, enable it
//UInt8 green = data[(pixelInfo + 1)]; // If you need this info, enable it
//UInt8 blue = data[pixelInfo + 2]; // If you need this info, enable it
UInt8 alpha = data[pixelInfo + 3]; // I need only this info for my maze game
CFRelease(pixelData);
//UIColor* color = [UIColor colorWithRed:red/255.0f green:green/255.0f blue:blue/255.0f alpha:alpha/255.0f]; // The pixel color info
if (alpha) return YES;
else return NO;
}
回答3:
OnTouch
-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [[touches allObjects] objectAtIndex:0];
CGPoint point1 = [touch locationInView:self.view];
touch = [[event allTouches] anyObject];
if ([touch view] == imgZoneWheel)
{
CGPoint location = [touch locationInView:imgZoneWheel];
[self getPixelColorAtLocation:location];
if(alpha==255)
{
NSLog(@"In Image Touch view alpha %d",alpha);
[self translateCurrentTouchPoint:point1.x :point1.y];
[imgZoneWheel setImage:[UIImage imageNamed:[NSString stringWithFormat:@"blue%d.png",GrndFild]]];
}
}
}
- (UIColor*) getPixelColorAtLocation:(CGPoint)point
{
UIColor* color = nil;
CGImageRef inImage;
inImage = imgZoneWheel.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));
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)];
}
// When finished, release the context
//CGContextRelease(cgctx);
// Free image data memory for the context
if (data) { free(data); }
return color;
}
- (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 = 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;
}
回答4:
Here's a generic method for getting pixel color in a UI image, building on Minas Petterson's answer:
- (UIColor*)pixelColorInImage:(UIImage*)image atX:(int)x atY:(int)y {
CFDataRef pixelData = CGDataProviderCopyData(CGImageGetDataProvider(image.CGImage));
const UInt8* data = CFDataGetBytePtr(pixelData);
int pixelInfo = ((image.size.width * y) + x ) * 4; // 4 bytes per pixel
UInt8 red = data[pixelInfo + 0];
UInt8 green = data[pixelInfo + 1];
UInt8 blue = data[pixelInfo + 2];
UInt8 alpha = data[pixelInfo + 3];
CFRelease(pixelData);
return [UIColor colorWithRed:red /255.0f
green:green/255.0f
blue:blue /255.0f
alpha:alpha/255.0f];
}
Note that X and Y may be swapped; this function accesses the underlying bitmap directly and doesn't consider rotations that may be part of the UIImage.
回答5:
Some Swift code based on Minas' answer. I've extended UIImage to make it accessible everywhere, and I've added some simple logic to guess the image format based on the pixel stride (1, 3, or 4)
Swift 3:
public extension UIImage {
func getPixelColor(point: CGPoint) -> UIColor {
guard let pixelData = CGDataProviderCopyData(CGImageGetDataProvider(self.CGImage)) else {
return UIColor.clearColor()
}
let data = CFDataGetBytePtr(pixelData)
let x = Int(point.x)
let y = Int(point.y)
let index = Int(self.size.width) * y + x
let expectedLengthA = Int(self.size.width * self.size.height)
let expectedLengthGrayScale = 2 * expectedLengthA
let expectedLengthRGB = 3 * expectedLengthA
let expectedLengthRGBA = 4 * expectedLengthA
let numBytes = CFDataGetLength(pixelData)
switch numBytes {
case expectedLengthA:
return UIColor(red: 0, green: 0, blue: 0, alpha: CGFloat(data[index])/255.0)
case expectedLengthGrayScale:
return UIColor(white: CGFloat(data[2 * index]) / 255.0, alpha: CGFloat(data[2 * index + 1]) / 255.0)
case expectedLengthRGB:
return UIColor(red: CGFloat(data[3*index])/255.0, green: CGFloat(data[3*index+1])/255.0, blue: CGFloat(data[3*index+2])/255.0, alpha: 1.0)
case expectedLengthRGBA:
return UIColor(red: CGFloat(data[4*index])/255.0, green: CGFloat(data[4*index+1])/255.0, blue: CGFloat(data[4*index+2])/255.0, alpha: CGFloat(data[4*index+3])/255.0)
default:
// unsupported format
return UIColor.clearColor()
}
}
}
Updated for Swift 4:
func getPixelColor(_ image:UIImage, _ point: CGPoint) -> UIColor {
let cgImage : CGImage = image.cgImage!
guard let pixelData = CGDataProvider(data: (cgImage.dataProvider?.data)!)?.data else {
return UIColor.clear
}
let data = CFDataGetBytePtr(pixelData)!
let x = Int(point.x)
let y = Int(point.y)
let index = Int(image.size.width) * y + x
let expectedLengthA = Int(image.size.width * image.size.height)
let expectedLengthGrayScale = 2 * expectedLengthA
let expectedLengthRGB = 3 * expectedLengthA
let expectedLengthRGBA = 4 * expectedLengthA
let numBytes = CFDataGetLength(pixelData)
switch numBytes {
case expectedLengthA:
return UIColor(red: 0, green: 0, blue: 0, alpha: CGFloat(data[index])/255.0)
case expectedLengthGrayScale:
return UIColor(white: CGFloat(data[2 * index]) / 255.0, alpha: CGFloat(data[2 * index + 1]) / 255.0)
case expectedLengthRGB:
return UIColor(red: CGFloat(data[3*index])/255.0, green: CGFloat(data[3*index+1])/255.0, blue: CGFloat(data[3*index+2])/255.0, alpha: 1.0)
case expectedLengthRGBA:
return UIColor(red: CGFloat(data[4*index])/255.0, green: CGFloat(data[4*index+1])/255.0, blue: CGFloat(data[4*index+2])/255.0, alpha: CGFloat(data[4*index+3])/255.0)
default:
// unsupported format
return UIColor.clear
}
}
回答6:
- (UIColor *)colorAtPixel:(CGPoint)point inImage:(UIImage *)image {
if (!CGRectContainsPoint(CGRectMake(0.0f, 0.0f, image.size.width, image.size.height), point)) {
return nil;
}
// Create a 1x1 pixel byte array and bitmap context to draw the pixel into.
NSInteger pointX = trunc(point.x);
NSInteger pointY = trunc(point.y);
CGImageRef cgImage = image.CGImage;
NSUInteger width = image.size.width;
NSUInteger height = image.size.height;
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
int bytesPerPixel = 4;
int bytesPerRow = bytesPerPixel * 1;
NSUInteger bitsPerComponent = 8;
unsigned char pixelData[4] = { 0, 0, 0, 0 };
CGContextRef context = CGBitmapContextCreate(pixelData, 1, 1, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
CGColorSpaceRelease(colorSpace);
CGContextSetBlendMode(context, kCGBlendModeCopy);
// Draw the pixel we are interested in onto the bitmap context
CGContextTranslateCTM(context, -pointX, pointY-(CGFloat)height);
CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, (CGFloat)width, (CGFloat)height), cgImage);
CGContextRelease(context);
// Convert color values [0..255] to floats [0.0..1.0]
CGFloat red = (CGFloat)pixelData[0] / 255.0f;
CGFloat green = (CGFloat)pixelData[1] / 255.0f;
CGFloat blue = (CGFloat)pixelData[2] / 255.0f;
CGFloat alpha = (CGFloat)pixelData[3] / 255.0f;
return [UIColor colorWithRed:red green:green blue:blue alpha:alpha];
}
回答7:
First of all create and attach tap gesture recognizer allow allow user interactions:
UITapGestureRecognizer * tapRecognizer = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(tapGesture:)];
[self.label addGestureRecognizer:tapRecognizer];
self.label.userInteractionEnabled = YES;
Now implement -tapGesture:
- (void)tapGesture:(UITapGestureRecognizer *)recognizer
{
CGPoint point = [recognizer locationInView:self.label];
UIGraphicsBeginImageContext(self.label.bounds.size);
CGContextRef context = UIGraphicsGetCurrentContext();
[self.label.layer renderInContext:context];
int bpr = CGBitmapContextGetBytesPerRow(context);
unsigned char * data = CGBitmapContextGetData(context);
if (data != NULL)
{
int offset = bpr*round(point.y) + 4*round(point.x);
int blue = data[offset+0];
int green = data[offset+1];
int red = data[offset+2];
int alpha = data[offset+3];
NSLog(@"%d %d %d %d", alpha, red, green, blue);
if (alpha == 0)
{
// Here is tap out of text
}
else
{
// Here is tap right into text
}
}
UIGraphicsEndImageContext();
}
This will works on UILabel with transparent background, if this is not what you want you can compare alpha, red, green, blue with self.label.backgroundColor...
来源：https://stackoverflow.com/questions/3284185/get-pixel-color-of-uiimage