修剪 UIImage 白色边框 [英] Trimming UIImage white borders
问题描述
我找不到裁剪包含白色边框的图像的方法.
I can't find a way to crop an image with white borders included.
目前它是一个 UIImage，我尝试了一些解决方案，例如 UIImage+Trim 和
Currently it's an UIImage, and I tried some solutions like UIImage+Trim and CKImageAddons but those libraries didn't work. I think part of the problem is that the borders is not perfectly white because of image compression (I think).
有没有人为此找到解决方案?
Has anyone find a solution for this?
谢谢，
推荐答案
嗯，我会使用 UIImage+Trim 并改变它的工作方式来计算明显的白色像素(所以如果 RGB > 255 - small_number_that_still_makes_it_white_but_suffices_to_cut_like_5_to_10)，不再计算非-透明.
Well, I would use UIImage+Trim and changed the way it works to count visibly white pixels (so if RGB > 255 - small_number_that_still_makes_it_white_but_suffices_to_cut_like_5_to_10) insted of counting non-transparent.
快速浏览后，计数循环在这里:
After quick look, the counting loop is here:
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]++;
}
}
}
}
和切割在下面完成，并删除等于0的rowSum和colSum.
and cutting is done below, and removes rowSum and colSum that are equal to 0.
此外，它似乎创建了用于计数的内部图像:
Also, it seems it creates inner image that is used for counting:
CGContextRef contextRef = CGBitmapContextCreate(bitmapData, (NSUInteger)width, (NSUInteger)height, 8, (NSUInteger)bytesPerRow, NULL, kCGImageAlphaOnly);
改用灰度图像应该是将其从透明度测试更改为颜色测试的简单方法.
Using a grayscale image instead should work as easy way to change it from transparency testing to color testing.
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;
}
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