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iphone - 是否可以以编程方式反转图像的颜色?

转载 作者:IT王子 更新时间:2023-10-29 08:04:17 24 4
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我想在 iOS 中拍摄图像并反转颜色。

最佳答案

为了扩展 quixoto 的答案,并且因为我有我自己项目的相关源代码,如果您需要转到 on-CPU 像素操作,那么我已经添加了说明的以下内容应该执行技巧:

@implementation UIImage (NegativeImage)

- (UIImage *)negativeImage
{
// get width and height as integers, since we'll be using them as
// array subscripts, etc, and this'll save a whole lot of casting
CGSize size = self.size;
int width = size.width;
int height = size.height;

// Create a suitable RGB+alpha bitmap context in BGRA colour space
CGColorSpaceRef colourSpace = CGColorSpaceCreateDeviceRGB();
unsigned char *memoryPool = (unsigned char *)calloc(width*height*4, 1);
CGContextRef context = CGBitmapContextCreate(memoryPool, width, height, 8, width * 4, colourSpace, kCGBitmapByteOrder32Big | kCGImageAlphaPremultipliedLast);
CGColorSpaceRelease(colourSpace);

// draw the current image to the newly created context
CGContextDrawImage(context, CGRectMake(0, 0, width, height), [self CGImage]);

// run through every pixel, a scan line at a time...
for(int y = 0; y < height; y++)
{
// get a pointer to the start of this scan line
unsigned char *linePointer = &memoryPool[y * width * 4];

// step through the pixels one by one...
for(int x = 0; x < width; x++)
{
// get RGB values. We're dealing with premultiplied alpha
// here, so we need to divide by the alpha channel (if it
// isn't zero, of course) to get uninflected RGB. We
// multiply by 255 to keep precision while still using
// integers
int r, g, b;
if(linePointer[3])
{
r = linePointer[0] * 255 / linePointer[3];
g = linePointer[1] * 255 / linePointer[3];
b = linePointer[2] * 255 / linePointer[3];
}
else
r = g = b = 0;

// perform the colour inversion
r = 255 - r;
g = 255 - g;
b = 255 - b;

// multiply by alpha again, divide by 255 to undo the
// scaling before, store the new values and advance
// the pointer we're reading pixel data from
linePointer[0] = r * linePointer[3] / 255;
linePointer[1] = g * linePointer[3] / 255;
linePointer[2] = b * linePointer[3] / 255;
linePointer += 4;
}
}

// get a CG image from the context, wrap that into a
// UIImage
CGImageRef cgImage = CGBitmapContextCreateImage(context);
UIImage *returnImage = [UIImage imageWithCGImage:cgImage];

// clean up
CGImageRelease(cgImage);
CGContextRelease(context);
free(memoryPool);

// and return
return returnImage;
}

@end

因此向 UIImage 添加了一个类别方法:

  1. 创建一个清晰的 CoreGraphics 位图上下文,它可以访问其内存
  2. 为它绘制 UIImage
  3. 遍历每个像素,从预乘的 alpha 转换为未变形的 RGB,分别反转每个 channel ,再次乘以 alpha 并存储回去
  4. 从上下文中获取图像并将其包装到 UIImage 中
  5. 自行清理并返回 UIImage

关于iphone - 是否可以以编程方式反转图像的颜色?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/6672517/

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