如何在 iPhone 上的图像上获取像素的 RGB 值 [英] How to get the RGB values for a pixel on an image on the iphone

问题描述

我正在编写一个 iPhone 应用程序，需要在本质上实现与 photoshop 中的吸管"工具等效的东西，您可以在其中触摸图像上的一个点并捕获相关像素的 RGB 值以确定并匹配其颜色.获取 UIImage 是简单的部分，但是有没有办法将 UIImage 数据转换为位图表示，在其中我可以为给定像素提取此信息?非常感谢提供工作代码示例，并注意我不关心 alpha 值.

I am writing an iPhone application and need to essentially implement something equivalent to the 'eyedropper' tool in photoshop, where you can touch a point on the image and capture the RGB values for the pixel in question to determine and match its color. Getting the UIImage is the easy part, but is there a way to convert the UIImage data into a bitmap representation in which I could extract this information for a given pixel? A working code sample would be most appreciated, and note that I am not concerned with the alpha value.

推荐答案

更多细节...

我今晚早些时候发布了对本页内容的整合和小补充 - 可以在这篇文章的底部找到.但是，我此时正在编辑帖子，以发布我建议的内容(至少对于我的要求，包括修改像素数据)是一种更好的方法，因为它提供了可写数据(而据我了解，提供的方法之前的帖子和这篇帖子的底部提供了对数据的只读参考).

A little more detail...

I posted earlier this evening with a consolidation and small addition to what had been said on this page - that can be found at the bottom of this post. I am editing the post at this point, however, to post what I propose is (at least for my requirements, which include modifying pixel data) a better method, as it provides writable data (whereas, as I understand it, the method provided by previous posts and at the bottom of this post provides a read-only reference to data).

方法一:可写像素信息

1. 我定义了常量

1. I defined constants

#define RGBA        4
#define RGBA_8_BIT  8

在我的 UIImage 子类中，我声明了实例变量:

In my UIImage subclass I declared instance variables:

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;

像素结构(在这个版本中带有 alpha)

The pixel struct (with alpha in this version)

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

位图函数(返回预先计算的 RGBA；将 RGB 除以 A 得到未修改的 RGB):

Bitmap function (returns pre-calculated RGBA; divide RGB by A to get unmodified 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;
}

<小时>

只读数据(以前的信息)- 方法 2:

<小时>

步骤 1. 我为字节声明了一个类型:

---

Read-Only Data (Previous information) - method 2:

---

Step 1. I declared a type for byte:

 typedef unsigned char byte;

第 2 步.我声明了一个结构体来对应一个像素:

Step 2. I declared a struct to correspond to a pixel:

 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):

Step 3. I subclassed UIImageView and declared (with corresponding synthesized properties):

//  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;

第 4 步.我在名为 bitmap 的方法中放置的子类代码(返回位图像素数据):

Step 4. Subclass code I put in a method named bitmap (to return the bitmap pixel data):

//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.我做了一个访问器方法:

Step 5. I made an accessor method:

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

这篇关于如何在 iPhone 上的图像上获取像素的 RGB 值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！