如何更改UIImage / UIImageView的单个像素的颜色

Question

我有一个UIImageView，我已应用过滤器：

testImageView.layer.magnificationFilter = kCAFilterNearest;

这样就可以看到各个像素。此UIImageView位于UIScrollView中，图像本身为1000x1000。我使用以下代码来检测已敲击的像素：

我首先设置了一个轻敲手势识别器：

UITapGestureRecognizer *scrollTap = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(singleTapGestureCaptured: )];
scrollTap.numberOfTapsRequired = 1;
[mainScrollView addGestureRecognizer:scrollTap];

然后使用tap的位置来产生点击UIImageView像素的点击坐标：

- (void)singleTapGestureCaptured:(UITapGestureRecognizer *)gesture
{
    CGPoint touchPoint = [gesture locationInView:testImageView];

    NSLog(@"%f is X pixel num, %f is Y pixel num ; %f is width of imageview", (touchPoint.x/testImageView.bounds.size.width)*1000, (touchPoint.y/testImageView.bounds.size.width)*1000, testImageView.bounds.size.width);

}

我希望能够点击一个像素，并改变它的颜色。但是，我找到的StackOverflow帖子都没有找到有效或未过时的答案。但是，对于熟练的编码人员，您可以帮助我破译较旧的帖子以制作有效的内容，或者使用我的上述代码自行生成一个简单的修复程序，以检测UIImageView的哪个像素已被点击。

所有帮助表示赞赏。

编辑原始用户2：

在关注originaluser2的帖子之后，当我在我的物理设备上运行它的示例GitHub项目时，运行代码非常有效。但是，当我在自己的应用程序中运行相同的代码时，我遇到的图像被替换为空格，并出现以下错误：

<Error>: Unsupported pixel description - 3 components, 16 bits-per-component, 64 bits-per-pixel
<Error>: CGBitmapContextCreateWithData: failed to create delegate.
<Error>: CGContextDrawImage: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
<Error>: CGBitmapContextCreateImage: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

代码清楚地起作用，正如我在手机上测试所证明的那样。但是，相同的代码在我自己的项目中产生了一些问题。虽然我怀疑它们都是由一两个简单的核心问题引起的。我该如何解决这些错误？

Answer 1

You'll want to break this problem up into multiple steps.

1. 获取图像坐标系中触摸点的坐标
2. 获取要更改的像素的x和y位置
3. 创建一个位图上下文，并用新颜色的组件替换给定像素的组件。

首先，要获得图像坐标系中触摸点的坐标 - 您可以使用我在UIImageView上编写的类别方法。这将返回一个CGAffineTransform，它将一个点从视图坐标映射到图像坐标 - 具体取决于视图的内容模式。

@interface UIImageView (PointConversionCatagory)

@property (nonatomic, readonly) CGAffineTransform viewToImageTransform;
@property (nonatomic, readonly) CGAffineTransform imageToViewTransform;

@end

@implementation UIImageView (PointConversionCatagory)

-(CGAffineTransform) viewToImageTransform {

    UIViewContentMode contentMode = self.contentMode;

    // failure conditions. If any of these are met – return the identity transform
    if (!self.image || self.frame.size.width == 0 || self.frame.size.height == 0 ||
        (contentMode != UIViewContentModeScaleToFill && contentMode != UIViewContentModeScaleAspectFill && contentMode != UIViewContentModeScaleAspectFit)) {
        return CGAffineTransformIdentity;
    }

    // the width and height ratios
    CGFloat rWidth = self.image.size.width/self.frame.size.width;
    CGFloat rHeight = self.image.size.height/self.frame.size.height;

    // whether the image will be scaled according to width
    BOOL imageWiderThanView = rWidth > rHeight;

    if (contentMode == UIViewContentModeScaleAspectFit || contentMode == UIViewContentModeScaleAspectFill) {

        // The ratio to scale both the x and y axis by
        CGFloat ratio = ((imageWiderThanView && contentMode == UIViewContentModeScaleAspectFit) || (!imageWiderThanView && contentMode == UIViewContentModeScaleAspectFill)) ? rWidth:rHeight;

        // The x-offset of the inner rect as it gets centered
        CGFloat xOffset = (self.image.size.width-(self.frame.size.width*ratio))*0.5;

        // The y-offset of the inner rect as it gets centered
        CGFloat yOffset = (self.image.size.height-(self.frame.size.height*ratio))*0.5;

        return CGAffineTransformConcat(CGAffineTransformMakeScale(ratio, ratio), CGAffineTransformMakeTranslation(xOffset, yOffset));
    } else {
        return CGAffineTransformMakeScale(rWidth, rHeight);
    }
}

-(CGAffineTransform) imageToViewTransform {
    return CGAffineTransformInvert(self.viewToImageTransform);
}

@end

这里没有什么太复杂，只是一些额外的尺度方面拟合/填充逻辑，以确保图像的居中被考虑在内。如果您在屏幕上以1：1显示图像，则可以完全跳过此步骤。

接下来，您需要更改像素的x和y位置。这很简单 - 您只想使用上面的类别属性viewToImageTransform来获取图像坐标系中的像素，然后使用floor使值成为积分。

UITapGestureRecognizer *tapGesture = [[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(imageViewWasTapped:)];
tapGesture.numberOfTapsRequired = 1;
[imageView addGestureRecognizer:tapGesture];

...

-(void) imageViewWasTapped:(UIGestureRecognizer*)tapGesture {

    if (!imageView.image) {
        return;
    }

    // get the pixel position
    CGPoint pt = CGPointApplyAffineTransform([tapGesture locationInView:imageView], imageView.viewToImageTransform);
    PixelPosition pixelPos = {(NSInteger)floor(pt.x), (NSInteger)floor(pt.y)};

    // replace image with new image, with the pixel replaced
    imageView.image = [imageView.image imageWithPixel:pixelPos replacedByColor:[UIColor colorWithRed:0 green:1 blue:1 alpha:1.0]];
}

最后，您将需要使用我的另一种类别方法 - imageWithPixel:replacedByColor:来获取具有给定颜色的替换像素的新图像。

/// A simple struct to represent the position of a pixel
struct PixelPosition {
    NSInteger x;
    NSInteger y;
};

typedef struct PixelPosition PixelPosition;

@interface UIImage (UIImagePixelManipulationCatagory)

@end

@implementation UIImage (UIImagePixelManipulationCatagory)

-(UIImage*) imageWithPixel:(PixelPosition)pixelPosition replacedByColor:(UIColor*)color {

    // components of replacement color – in a 255 UInt8 format (fairly standard bitmap format)
    const CGFloat* colorComponents = CGColorGetComponents(color.CGColor);
    UInt8* color255Components = calloc(sizeof(UInt8), 4);
    for (int i = 0; i < 4; i++) color255Components[i] = (UInt8)round(colorComponents[i]*255.0);

    // raw image reference
    CGImageRef rawImage = self.CGImage;

    // image attributes
    size_t width = CGImageGetWidth(rawImage);
    size_t height = CGImageGetHeight(rawImage);
    CGRect rect = {CGPointZero, {width, height}};

    // image format
    size_t bitsPerComponent = 8;
    size_t bytesPerRow = width*4;

    // the bitmap info
    CGBitmapInfo bitmapInfo = kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big;

    // data pointer – stores an array of the pixel components. For example (r0, b0, g0, a0, r1, g1, b1, a1 .... rn, gn, bn, an)
    UInt8* data = calloc(bytesPerRow, height);

    // get new RGB color space
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

    // create bitmap context
    CGContextRef ctx = CGBitmapContextCreate(data, width, height, bitsPerComponent, bytesPerRow, colorSpace, bitmapInfo);

    // draw image into context (populating the data array while doing so)
    CGContextDrawImage(ctx, rect, rawImage);

    // get the index of the pixel (4 components times the x position plus the y position times the row width)
    NSInteger pixelIndex = 4*(pixelPosition.x+(pixelPosition.y*width));

    // set the pixel components to the color components
    data[pixelIndex] = color255Components[0]; // r
    data[pixelIndex+1] = color255Components[1]; // g
    data[pixelIndex+2] = color255Components[2]; // b
    data[pixelIndex+3] = color255Components[3]; // a

    // get image from context
    CGImageRef img = CGBitmapContextCreateImage(ctx);

    // clean up
    free(color255Components);
    CGContextRelease(ctx);
    CGColorSpaceRelease(colorSpace);
    free(data);

    UIImage* returnImage = [UIImage imageWithCGImage:img];
    CGImageRelease(img);

    return returnImage;
}

@end

这样做首先以255 UInt8格式输出要写入其中一个像素的颜色分量。接下来，它使用输入图像的给定属性创建一个新的位图上下文。

这个方法的重点是：

// get the index of the pixel (4 components times the x position plus the y position times the row width)
NSInteger pixelIndex = 4*(pixelPosition.x+(pixelPosition.y*width));

// set the pixel components to the color components
data[pixelIndex] = color255Components[0]; // r
data[pixelIndex+1] = color255Components[1]; // g
data[pixelIndex+2] = color255Components[2]; // b
data[pixelIndex+3] = color255Components[3]; // a

这样做是得出给定像素的索引（基于像素的x和y坐标） - 然后使用该索引将该像素的组件数据替换为替换颜色的颜色分量。

最后，我们从位图上下文中获取一个图像并执行一些清理。

完成结果：

---

完整项目：https://github.com/hamishknight/Pixel-Color-Changing

Answer 2

您可以尝试以下内容：

UIImage *originalImage = [UIImage imageNamed:@"something"];

CGSize size = originalImage.size;

UIGraphicsBeginImageContext(size);

[originalImage drawInRect:CGRectMake(0, 0, size.width, size.height)];

// myColor is an instance of UIColor
[myColor setFill];
UIRectFill(CGRectMake(someX, someY, 1, 1);

UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();