最近在改的需求，需要裁剪圖片，然后網(wǎng)上各種搜索，終于尋得一個仿微信頭像裁剪的demo，改一改基本OK。但是第一次裁剪完的圖片有些模糊，網(wǎng)上看帖子，有人提議把UIGraphicsBeginImageContext(size);這行代碼改成如下形式：UIGraphicsBeginImageContextWithOptions(size,NO,kDeviceScale);這樣的話，加了屏幕分辨率，縮放以后準備裁剪的圖片確實不模糊了，但是誕生了一個新的問題，明明圖片已經調整到裁剪框的中心也縮放到了想要的內容范圍，但是裁剪以后的結果是只有圖片右上角的1/4,好苦逼啊，然后又是各種嘗試，各種問大神，最后又是分辨率的問題，擦，想死的節(jié)奏！記錄一下給需要用到裁剪功能的同學提個醒，與及給正在為此問題煩惱的同學予希望之光。

- (UIImage *)getSubImage {
    
    CGRect squareFrame = self.cropFrame;
    
    CGFloat scaleRatio = self.latestFrame.size.width / self.originalImage.size.width;
    CGFloat x = (squareFrame.origin.x - self.latestFrame.origin.x) / scaleRatio;
    CGFloat y = (squareFrame.origin.y - self.latestFrame.origin.y) / scaleRatio;
    CGFloat w = squareFrame.size.width / scaleRatio;
    CGFloat h = squareFrame.size.width / scaleRatio;
    if (self.latestFrame.size.width < self.cropFrame.size.width) {
        CGFloat newW = self.originalImage.size.width;
        CGFloat newH = newW * (self.cropFrame.size.height / self.cropFrame.size.width);
        x = 0; y = y + (h - newH) / 2;
        w = newH; h = newH;
    }
    if (self.latestFrame.size.height < self.cropFrame.size.height) {
        CGFloat newH = self.originalImage.size.height;
        CGFloat newW = newH * (self.cropFrame.size.width / self.cropFrame.size.height);
        x = x + (w - newW) / 2; y = 0;
        w = newH; h = newH;
    }
    //乘以圖片的分辨率，保證截到一張完整的圖（分辨率：kDeviceScale）
    CGRect myImageRect = CGRectMake(x*kDeviceScale,y*kDeviceScale, w*kDeviceScale, h*kDeviceScale);
    CGImageRef imageRef = self.originalImage.CGImage;
    CGImageRef subImageRef = CGImageCreateWithImageInRect(imageRef, myImageRect);
    CGSize size;
    size.width = myImageRect.size.width;
    size.height = myImageRect.size.height;
    //UIGraphicsBeginImageContext(size);
    //設置圖片的分辨率，保證圖片的清晰度(kDeviceScale)
    UIGraphicsBeginImageContextWithOptions(size,NO,kDeviceScale);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextDrawImage(context, myImageRect, subImageRef);
    UIImage *smallImage = [UIImage imageWithCGImage:subImageRef];
    CGImageRelease(subImageRef);
    UIGraphicsEndImageContext();
    return smallImage;
}