本文實例講解了iOS從背景圖中取色的代碼，分享給大家供大家參考，具體內容如下

實現代碼：

void *bitmapData; //內存空間的指針，該內存空間的大小等於圖像使用RGB通道所占用的字節數。
 
static CGContextRef CreateRGBABitmapContext (CGImageRef inImage)
{
  CGContextRef context = NULL;
  CGColorSpaceRef colorSpace;
  int bitmapByteCount;
  int bitmapBytesPerRow;
 
  size_t pixelsWide = CGImageGetWidth(inImage); //獲取橫向的像素點的個數
  size_t pixelsHigh = CGImageGetHeight(inImage);
 
  bitmapBytesPerRow  = (pixelsWide * 4); //每一行的像素點占用的字節數，每個像素點的ARGB四個通道各占8個bit(0-255)的空間
  bitmapByteCount = (bitmapBytesPerRow * pixelsHigh); //計算整張圖占用的字節數
 
  colorSpace = CGColorSpaceCreateDeviceRGB();//創建依賴於設備的RGB通道
  //分配足夠容納圖片字節數的內存空間
  bitmapData = malloc( bitmapByteCount );
  //創建CoreGraphic的圖形上下文，該上下文描述了bitmaData指向的內存空間需要繪制的圖像的一些繪制參數
  context = CGBitmapContextCreate (bitmapData,
                   pixelsWide,
                   pixelsHigh,
                   8,
                   bitmapBytesPerRow,
                   colorSpace,
                   kCGImageAlphaPremultipliedLast);
  //Core Foundation中通過含有Create、Alloc的方法名字創建的指針，需要使用CFRelease()函數釋放
  CGColorSpaceRelease( colorSpace );
  return context;
}
 
// 返回一個指針，該指針指向一個數組，數組中的每四個元素都是圖像上的一個像素點的RGBA的數值(0-255)，用無符號的char是因為它正好的取值范圍就是0-255
static unsigned char *RequestImagePixelData(UIImage *inImage)
{
  CGImageRef img = [inImage CGImage];
  CGSize size = [inImage size];
  //使用上面的函數創建上下文
  CGContextRef cgctx = CreateRGBABitmapContext(img);
  CGRect rect = {{0,0},{size.width, size.height}};
  //將目標圖像繪制到指定的上下文，實際為上下文內的bitmapData。
  CGContextDrawImage(cgctx, rect, img);
  unsigned char *data = CGBitmapContextGetData (cgctx);
  //釋放上面的函數創建的上下文
  CGContextRelease(cgctx);
  return data;
}
 
//設置背景原圖片,即取色所用的圖片
- (void)setSourceImage:(NSString *)sourceImage ImageWidth:(int)_width ImageHeight:(int)_height {
  //生成指定大小的背景圖
  UIImage *im = [UIImage imageNamed:sourceImage];
  UIImage *newImage;
  UIImageView *view = [[UIImageView alloc] initWithImage:im];
  view.frame = CGRectMake(0, 0, _width, _height);
  UIGraphicsBeginImageContext(CGSizeMake(_width, _height)); //size 為CGSize類型，即你所需要的圖片尺寸
  [im drawInRect:CGRectMake(0, 0, _width, _height)]; //newImageRect指定了圖片繪制區域
  newImage = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
 
  width = newImage.size.width;
  height = newImage.size.height;
  //將解析背景圖為像素，供取色用
  imgPixel = RequestImagePixelData(newImage);
}
 
//計算顏色
-(UIColor*)calColor:(CGPoint)aPoint {
  int i = 4 * width * round(aPoint.y+imageView.frame.size.height/2) + 4 * round(aPoint.x+imageView.frame.size.width/2);
  int _r = (unsigned char)imgPixel[i];
  int _g = (unsigned char)imgPixel[i+1];
  int _b = (unsigned char)imgPixel[i+2];
  NSLog(@"(%f,%f)",aPoint.x,aPoint.y);
  NSLog(@"Red : %f  Green: %f  Blue: %f",_r/255.0,_g/255.0,_b/255.0);
  return [UIColor colorWithRed:_r/255.0f green:_g/255.0f blue:_b/255.0f alpha:1.0];
}  
 
- (void)changColor:(UIColor *)color{
  int width_;
  if (![Util isIpad]) {
    width_ = 30;
  } else {
    width_ = 70;
  }
 
  UIGraphicsBeginImageContext(CGSizeMake(width_, width_));
  CGContextRef ctx = UIGraphicsGetCurrentContext();
  CGContextMoveToPoint(ctx, 20, 20);
  CGContextSetFillColorWithColor(ctx, color.CGColor);
  if (![Util isIpad]) {
    CGContextAddArc(ctx, width_/2, width_/2, 14.5, 0, 6.3, 0);
  } else {
    CGContextAddArc(ctx, width_/2+0.5, width_/2, 31.3, 0, 6.3, 0);
  }
  CGContextFillPath(ctx);
  self->pickedColorImageView.image = UIGraphicsGetImageFromCurrentImageContext();
  UIGraphicsEndImageContext();
}

以上就是本文的全部內容，希望對大家的學習有所幫助。