如何获取iphone上图像上像素的RGB值

Question

我正在编写一个iPhone应用程序,并且需要在photoshop中实现与"eyedropper"工具相当的东西,在那里你可以触摸图像上的一个点并捕获相关像素的RGB值,以确定和匹配它的颜色.获取UIImage是一个简单的部分,但有没有办法将UIImage数据转换为位图表示,我可以在其中提取给定像素的信息？一个工作代码示例将是最受欢迎的,并注意我不关心alpha值.

Answer 1

更多细节......

我今天早些时候发布了一个合并,并在此页面上说了一些小补充 - 可以在这篇文章的底部找到.我正在编辑帖子,但是,发布我的建议(至少对我的要求,包括修改像素数据)一个更好的方法,因为它提供可写数据(而我据了解,提供的方法)通过以前的帖子和这篇文章的底部提供了对数据的只读参考.

方法1:可写像素信息

1. 我定义了常量

   #define RGBA        4
   #define RGBA_8_BIT  8
   

2. 在我的UIImage子类中,我声明了实例变量:

   size_t bytesPerRow;
   size_t byteCount;
   size_t pixelCount;
   
   CGContextRef context;
   CGColorSpaceRef colorSpace;
   
   UInt8 *pixelByteData;
   // A pointer to an array of RGBA bytes in memory
   RPVW_RGBAPixel *pixelData;
   

3. 像素结构(此版本中带有alpha)

   typedef struct RGBAPixel {
       byte red;
       byte green;
       byte blue;
       byte alpha;
   } RGBAPixel;
   

4. 位图功能(返回预先计算的RGBA;将RGB除以A得到未修改的RGB):

   -(RGBAPixel*) bitmap {
       NSLog( @"Returning bitmap representation of UIImage." );
       // 8 bits each of red, green, blue, and alpha.
       [self setBytesPerRow:self.size.width * RGBA];
       [self setByteCount:bytesPerRow * self.size.height];
       [self setPixelCount:self.size.width * self.size.height];
   
       // Create RGB color space
       [self setColorSpace:CGColorSpaceCreateDeviceRGB()];
   
       if (!colorSpace)
       {
           NSLog(@"Error allocating color space.");
           return nil;
       }
   
       [self setPixelData:malloc(byteCount)];
   
       if (!pixelData)
       {
           NSLog(@"Error allocating bitmap memory. Releasing color space.");
           CGColorSpaceRelease(colorSpace);
   
           return nil;
       }
   
       // Create the bitmap context. 
       // Pre-multiplied RGBA, 8-bits per component. 
       // The source image format will be converted to the format specified here by CGBitmapContextCreate.
       [self setContext:CGBitmapContextCreate(
                                              (void*)pixelData,
                                              self.size.width,
                                              self.size.height,
                                              RGBA_8_BIT,
                                              bytesPerRow,
                                              colorSpace,
                                              kCGImageAlphaPremultipliedLast
                                              )];
   
       // Make sure we have our context
       if (!context)   {
           free(pixelData);
           NSLog(@"Context not created!");
       }
   
       // Draw the image to the bitmap context. 
       // The memory allocated for the context for rendering will then contain the raw image pixelData in the specified color space.
       CGRect rect = { { 0 , 0 }, { self.size.width, self.size.height } };
   
       CGContextDrawImage( context, rect, self.CGImage );
   
       // Now we can get a pointer to the image pixelData associated with the bitmap context.
       pixelData = (RGBAPixel*) CGBitmapContextGetData(context);
   
       return pixelData;
   }
   

只读数据(以前的信息) - 方法2:

步骤1.我声明了一个字节类型:

 typedef unsigned char byte;

第2步.我声明了一个与像素对应的结构:

 typedef struct RGBPixel{
    byte red;
    byte green;
    byte blue;  
    }   
RGBPixel;

第3步.我将UIImageView子类化并声明(具有相应的合成属性):

//  Reference to Quartz CGImage for receiver (self)  
CFDataRef bitmapData;   

//  Buffer holding raw pixel data copied from Quartz CGImage held in receiver (self)    
UInt8* pixelByteData;

//  A pointer to the first pixel element in an array    
RGBPixel* pixelData;

步骤4.子类代码我放入一个名为bitmap的方法(返回位图像素数据):

//Get the bitmap data from the receiver's CGImage (see UIImage docs)  
[self setBitmapData: CGDataProviderCopyData(CGImageGetDataProvider([self CGImage]))];

//Create a buffer to store bitmap data (unitialized memory as long as the data)    
[self setPixelBitData:malloc(CFDataGetLength(bitmapData))];

//Copy image data into allocated buffer    
CFDataGetBytes(bitmapData,CFRangeMake(0,CFDataGetLength(bitmapData)),pixelByteData);

//Cast a pointer to the first element of pixelByteData    
//Essentially what we're doing is making a second pointer that divides the byteData's units differently - instead of dividing each unit as 1 byte we will divide each unit as 3 bytes (1 pixel).    
pixelData = (RGBPixel*) pixelByteData;

//Now you can access pixels by index: pixelData[ index ]    
NSLog(@"Pixel data one red (%i), green (%i), blue (%i).", pixelData[0].red, pixelData[0].green, pixelData[0].blue);

//You can determine the desired index by multiplying row * column.    
return pixelData;

第5步.我制作了一个访问方法:

-(RGBPixel*)pixelDataForRow:(int)row column:(int)column{
    //Return a pointer to the pixel data
    return &pixelData[row * column];           
}

Answer 2

这是我对UIImage采样颜色的解决方案.

此方法将请求的像素渲染为1px大型RGBA缓冲区,并将生成的颜色值作为UIColor对象返回.这比我见过的大多数其他方法快得多,并且只使用很少的内存.

对于像颜色选择器这样的东西,它应该可以很好地工作,在任何给定的时间你通常只需要一个特定像素的值.

的UIImage + Picker.h

#import <UIKit/UIKit.h>


@interface UIImage (Picker)

- (UIColor *)colorAtPosition:(CGPoint)position;

@end

的UIImage + Picker.m

#import "UIImage+Picker.h"


@implementation UIImage (Picker)

- (UIColor *)colorAtPosition:(CGPoint)position {

    CGRect sourceRect = CGRectMake(position.x, position.y, 1.f, 1.f);
    CGImageRef imageRef = CGImageCreateWithImageInRect(self.CGImage, sourceRect);

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    unsigned char *buffer = malloc(4);
    CGBitmapInfo bitmapInfo = kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big;
    CGContextRef context = CGBitmapContextCreate(buffer, 1, 1, 8, 4, colorSpace, bitmapInfo);
    CGColorSpaceRelease(colorSpace);
    CGContextDrawImage(context, CGRectMake(0.f, 0.f, 1.f, 1.f), imageRef);
    CGImageRelease(imageRef);
    CGContextRelease(context);

    CGFloat r = buffer[0] / 255.f;
    CGFloat g = buffer[1] / 255.f;
    CGFloat b = buffer[2] / 255.f;
    CGFloat a = buffer[3] / 255.f;

    free(buffer);

    return [UIColor colorWithRed:r green:g blue:b alpha:a];
}

@end 

Answer 3

您无法直接访问UIImage的位图数据.

您需要获取UIImage的CGImage表示.然后从位图的CFData表示中获取CGImage的数据提供程序.确保在完成后释放CFData.

CGImageRef cgImage = [image CGImage];
CGDataProviderRef provider = CGImageGetDataProvider(cgImage);
CFDataRef bitmapData = CGDataProviderCopyData(provider);

您可能希望查看CGImage的位图信息以获取像素顺序,图像尺寸等.

Answer 4

Lajos的回答对我有用.为了将像素数据作为字节数组,我这样做了:

UInt8* data = CFDataGetBytePtr(bitmapData);

更多信息:CFDataRef 文档.

此外,请记住包括 CoreGraphics.framework