Core Graphics - 使用整数数组绘制灰度图像

Question

我正在尝试使用核心图形创建 UIImage。

我的愿望是绘制一个分为4个不同灰度的图像areas/pixels。

.....白色....灰色.....

.....灰色.....黑色...

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

int8_t data[] = {
    255,   122,
    122,     0,
};

255是白色，

122是灰色的，

0是黑色

我能找到的类似代码的最佳参考是 here

这个参考引用了一个 RGB 图像，所以根据我自己的常识想出了这个代码（抱歉 objective-C 法语 - 这不是我的参考 :)）：

- (UIImage *)getImageFromGrayScaleArray {
    
    int width = 2;
    int height = 2;
  
    int8_t data[] = {
        255, 122,
        122, 0,
    };

    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...这段代码给了我这个全黑的 UIImage：

有人可以向我介绍我可以阅读和理解如何完成这样的任务的地方吗？尝试执行此类任务时，有关核心图形的数据量似乎非常稀缺。所有这些猜测的时间......永远:)

Answer 1

你很接近...

灰度图像每个像素需要两个分量：亮度和 alpha。

因此，只需进行一些更改（参见评论）：

- (UIImage *)getImageFromGrayScaleArray {
    
    int width = 2;
    int height = 2;
    
    // 1 byte for brightness, 1 byte for alpha
    int8_t data[] = {
        255, 255,
        122, 255,
        122, 255,
        0, 255,
    };
    
    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];
}

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

尝试使用修改后的代码：

@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, 122,
        122, 0,
    };
    
    int8_t blackArray[] = {
        0, 0,
        0, 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, 255, 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,
                                        height,
                                        8,
                                        8 * bytesPerPixel,
                                        width * bytesPerPixel,
                                        colorSpaceRef,
                                        kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big,
                                        provider,
                                        NULL,
                                        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, 122,
        122, 0,
    };

底部图片使用：

    int8_t blackArray[] = {
        0, 0,
        0, 0,
    };

输出：

Core Graphics - 使用整数数组绘制灰度图像

Core Graphics - draw a gray scale image using array of integers

core-graphics

cgimage

ios