Core Graphics - 使用整数数组绘制灰度图像

问题描述

我正在尝试使用核心图形创建 UIImage。

我的愿望是将图像划分为 4 个不同的灰度区域/像素。

....白色....灰色.....

.....灰色.....黑色...

所以使用核心图形，我想定义一个由 4 个不同的 int8_t 组成的数组，它们对应于所需的图像：

int8_t data[] = {
    255,122,};

255 是白色的，

122 为灰色，

0 是黑色的

我能找到的类似代码的最佳参考是 here

这个引用指的是一个 RGB 图像，所以根据我自己的常识想出了这个代码（对不起，objective-C 法语 - 这不是我的引用:)）：

- (UIImage *)getImageFromGrayScaleArray {
    
    int width = 2;
    int height = 2;
  
    int8_t data[] = {
        255,};

    CGDataProviderRef provider = CGDataProviderCreateWithData (NULL,&data[0],width * height,NULL);

    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceGray();
    
    CGImageRef imageRef = CGImageCreate (width,height,[self bitsPerComponent],[self bitsPerPixel],width * [self bytesPerPixel],colorSpaceRef,kCGBitmapByteOrderDefault,provider,NULL,NO,kCGRenderingIntentDefault);
    UIImage *image = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpaceRef);
    
    return image;
}


- (int)bitsPerPixel {
    return 8 * [self bytesPerPixel];;
}

- (int)bytesPerPixel {
    return [self bytesPerComponent] * [self componentsPerPixel];
}

- (int)componentsPerPixel {
    return 1;
}

- (int)bytesPerComponent {
    return 1;
}

- (int)bitsPerComponent {
    return 8 * [self bytesPerComponent];
}

但是……这段代码给了我整个黑色的 UIImage：

有人可以参考我可以阅读和理解如何完成这样的任务吗？在尝试执行此类任务时，有关核心图形的数据量似乎非常稀少。所有这些猜测的时间......永远:)

解决方法

你很接近...

灰度图像每个像素需要两个组件：亮度和 alpha。

因此，只需进行一些更改（请参阅评论）：

- (UIImage *)getImageFromGrayScaleArray {
    
    int width = 2;
    int height = 2;
    
    // 1 byte for brightness,1 byte for alpha
    int8_t data[] = {
        255,255,122,};
    
    CGDataProviderRef provider = CGDataProviderCreateWithData (NULL,&data[0],// size is width * height * bytesPerPixel
                                                               width * height * [self bytesPerPixel],NULL);
    
    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceGray();
    
    CGImageRef imageRef = CGImageCreate (width,height,[self bitsPerComponent],[self bitsPerPixel],width * [self bytesPerPixel],colorSpaceRef,// use this
                                         kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big,// instead of this
                                         //kCGBitmapByteOrderDefault,provider,NULL,NO,kCGRenderingIntentDefault);
    
    UIImage *image = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpaceRef);
    
    return image;
}


- (int)bitsPerPixel {
    return 8 * [self bytesPerPixel];;
}

- (int)bytesPerPixel {
    return [self bytesPerComponent] * [self componentsPerPixel];
}

- (int)componentsPerPixel {
    return 2;  // 1 byte for brightness,1 byte for alpha
}

- (int)bytesPerComponent {
    return 1;
}

- (int)bitsPerComponent {
    return 8 * [self bytesPerComponent];
}

---

编辑 -- 我认为使用上述代码的内存缓冲区寻址存在问题。经过一些测试，我得到了不一致的结果。

试试这个修改后的代码：

@interface TestingViewController : UIViewController
@end
@interface TestingViewController ()
@end
@implementation TestingViewController

// CGDataProviderCreateWithData callback to free the pixel data buffer
void freePixelData(void *info,const void *data,size_t size) {
    free((void *)data);
}

- (UIImage*) getImageFromGrayScaleArray:(BOOL)allBlack {
    
    int8_t grayArray[] = {
        255,};
    
    int8_t blackArray[] = {
        0,};
    
    int width = 2;
    int height = 2;
    
    int imageSizeInPixels = width * height;
    int bytesPerPixel = 2; // 1 byte for brightness,1 byte for alpha
    unsigned char *pixels = (unsigned char *)malloc(imageSizeInPixels * bytesPerPixel);
    memset(pixels,imageSizeInPixels * bytesPerPixel); // setting alpha values to 255
    
    if (allBlack) {
        for (int i = 0; i < imageSizeInPixels; i++) {
            pixels[i * 2] = blackArray[i]; // writing array of bytes as image brightnesses
        }
    } else {
        for (int i = 0; i < imageSizeInPixels; i++) {
            pixels[i * 2] = grayArray[i]; // writing array of bytes as image brightnesses
        }
    }
    
    CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceGray();
    CGDataProviderRef provider = CGDataProviderCreateWithData(NULL,pixels,imageSizeInPixels * bytesPerPixel,freePixelData);
    
    CGImageRef imageRef = CGImageCreate(width,8,8 * bytesPerPixel,width * bytesPerPixel,kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big,false,kCGRenderingIntentDefault);
    
    UIImage *image = [UIImage imageWithCGImage:imageRef];
    
    CGImageRelease(imageRef);
    CGDataProviderRelease(provider);
    CGColorSpaceRelease(colorSpaceRef);
    
    return image;
}

- (void)viewDidLoad {
    [super viewDidLoad];
    
    self.view.backgroundColor = [UIColor systemTealColor];
    
    UIImage *img1 = [self getImageFromGrayScaleArray:NO];
    UIImage *img2 = [self getImageFromGrayScaleArray:YES];
    
    UIImageView *v1 = [UIImageView new];
    UIImageView *v2 = [UIImageView new];
    
    v1.image = img1;
    v1.backgroundColor = [UIColor systemYellowColor];
    v2.image = img2;
    v2.backgroundColor = [UIColor systemYellowColor];
    
    v1.contentMode = UIViewContentModeScaleToFill;
    v2.contentMode = UIViewContentModeScaleToFill;
    
    v1.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:v1];
    v2.translatesAutoresizingMaskIntoConstraints = NO;
    [self.view addSubview:v2];
    
    UILayoutGuide *g = [self.view safeAreaLayoutGuide];
    
    [NSLayoutConstraint activateConstraints:@[
        
        [v1.topAnchor constraintEqualToAnchor:g.topAnchor constant:40.0],[v1.centerXAnchor constraintEqualToAnchor:g.centerXAnchor],[v1.widthAnchor constraintEqualToConstant:200.0],[v1.heightAnchor constraintEqualToAnchor:v1.widthAnchor],[v2.topAnchor constraintEqualToAnchor:v1.bottomAnchor constant:40.0],[v2.centerXAnchor constraintEqualToAnchor:self.view.centerXAnchor],[v2.widthAnchor constraintEqualToAnchor:v1.widthAnchor],[v2.heightAnchor constraintEqualToAnchor:v2.widthAnchor],]];
}

@end

我们添加两个 200x200 图像视图，并使用以下方法将顶部 .image 设置为返回的 UIImage：

    int8_t grayArray[] = {
        255,};
    

和底部图像使用：

    int8_t blackArray[] = {
        0,};
    

输出：