修剪 UIImage 白色边框

Question

我找不到一种方法来裁剪包含白色边框的图像。

目前它是一个 UIImage，我尝试了一些解决方案，例如UIImage+Trim和CKImageAddons，但这些库不起作用。我认为部分问题是由于图像压缩，边框不是完全白色（我认为）。

有人找到解决方案吗？

谢谢，

Answer 1

好吧，我会使用 UIImage+Trim 并更改其计算可见白色像素的方式（因此，如果 RGB > 255 -small_number_that_still_makes_it_white_but_suffices_to_cut_like_5_to_10），而不是计算不透明。

快速查看后，计数循环在这里：

for (NSInteger row = 0; row < height; row++) {

    for (NSInteger col = 0; col < width; col++) {

        if (fullyOpaque) {

            // Found non-transparent pixel
            if (bitmapData[row*bytesPerRow + col] == UINT8_MAX) {

                rowSum[row]++;
                colSum[col]++;

            }

        } else {

            // Found non-transparent pixel
            if (bitmapData[row*bytesPerRow + col]) {

                rowSum[row]++;
                colSum[col]++;

            }

        }

    }

}

下面进行裁剪，去掉rowSum和colSum等于0的部分。

另外，它似乎创建了用于计数的内部图像：

CGContextRef contextRef = CGBitmapContextCreate(bitmapData, (NSUInteger)width, (NSUInteger)height, 8, (NSUInteger)bytesPerRow, NULL, kCGImageAlphaOnly);

使用灰度图像应该可以作为将其从透明度测试更改为颜色测试的简单方法。

编辑：好的，解决方案：

- (UIEdgeInsets)transparencyInsetsByCuttingWhitespace:(UInt8)tolerance
{
    // Draw our image on that context
    NSInteger width  = (NSInteger)CGImageGetWidth([self CGImage]);
    NSInteger height = (NSInteger)CGImageGetHeight([self CGImage]);
    NSInteger bytesPerRow = width * (NSInteger)sizeof(uint8_t);

    // Allocate array to hold alpha channel
    uint8_t * bitmapData = calloc((size_t)(width * height), sizeof(uint8_t));

    // Create grayscale image
    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceGray();
    CGContextRef contextRef = CGBitmapContextCreate(bitmapData, (NSUInteger)width, (NSUInteger)height, 8, (NSUInteger)bytesPerRow, colorSpace, kCGImageAlphaNone);

    CGImageRef cgImage = self.CGImage;
    CGRect rect = CGRectMake(0, 0, width, height);
    CGContextDrawImage(contextRef, rect, cgImage);

    // Sum all non-transparent pixels in every row and every column
    uint16_t * rowSum = calloc((size_t)height, sizeof(uint16_t));
    uint16_t * colSum = calloc((size_t)width,  sizeof(uint16_t));

    // Enumerate through all pixels
    for (NSInteger row = 0; row < height; row++) {

        for (NSInteger col = 0; col < width; col++) {

            // Found darker pixel
            if (bitmapData[row*bytesPerRow + col] <= UINT8_MAX - tolerance) {

                rowSum[row]++;
                colSum[col]++;

            }
        }
    }

    // Initialize crop insets and enumerate cols/rows arrays until we find non-empty columns or row
    UIEdgeInsets crop = UIEdgeInsetsZero;

    // Top
    for (NSInteger i = 0; i < height; i++) {

        if (rowSum[i] > 0) {

            crop.top = i;
            break;

        }

    }

    // Bottom
    for (NSInteger i = height - 1; i >= 0; i--) {

        if (rowSum[i] > 0) {
            crop.bottom = MAX(0, height - i - 1);
            break;
        }

    }

    // Left
    for (NSInteger i = 0; i < width; i++) {

        if (colSum[i] > 0) {
            crop.left = i;
            break;
        }

    }

    // Right
    for (NSInteger i = width - 1; i >= 0; i--) {

        if (colSum[i] > 0) {

            crop.right = MAX(0, width - i - 1);
            break;

        }
    }

    free(bitmapData);
    free(colSum);
    free(rowSum);

    CGContextRelease(contextRef);

    return crop;
}

- (UIImage *)imageByTrimmingWhitePixelsWithOpacity:(UInt8)tolerance
{
    if (self.size.height < 2 || self.size.width < 2) {

        return self;

    }

    CGRect rect = CGRectMake(0, 0, self.size.width * self.scale, self.size.height * self.scale);
    UIEdgeInsets crop = [self transparencyInsetsByCuttingWhitespace:tolerance];

    UIImage *img = self;

    if (crop.top == 0 && crop.bottom == 0 && crop.left == 0 && crop.right == 0) {

        // No cropping needed

    } else {

        // Calculate new crop bounds
        rect.origin.x += crop.left;
        rect.origin.y += crop.top;
        rect.size.width -= crop.left + crop.right;
        rect.size.height -= crop.top + crop.bottom;

        // Crop it
        CGImageRef newImage = CGImageCreateWithImageInRect([self CGImage], rect);

        // Convert back to UIImage
        img = [UIImage imageWithCGImage:newImage scale:self.scale orientation:self.imageOrientation];

        CGImageRelease(newImage);
    }

    return img;
}