在iPhone上切片UIImage

目标:取一个UIImage,在中间裁剪出一个正方形,将正方形的大小改为320x320像素,将图像切割成16个80x80图像,将16个图像保存在一个数组中.

这是我的代码:

CGImageRef originalImage, resizedImage, finalImage, tmp;
float imgWidth, imgHeight, diff;
UIImage *squareImage, *playImage;
NSMutableArray *tileImgArray;
int r, c;

originalImage = [image CGImage];

imgWidth = image.size.width;
imgHeight = image.size.height;
diff = fabs(imgWidth - imgHeight);

if(imgWidth > imgHeight){
    resizedImage = CGImageCreateWithImageInRect(originalImage, CGRectMake(floor(diff/2), 0, imgHeight, imgHeight));
}else{
    resizedImage = CGImageCreateWithImageInRect(originalImage, CGRectMake(0, floor(diff/2), imgWidth, imgWidth));
}
CGImageRelease(originalImage);

squareImage = [UIImage imageWithCGImage:resizedImage];      
if(squareImage.size.width != squareImage.size.height){
    NSLog(@"image cutout error!");
    //*code to return to main menu of app, irrelevant here
}else{
    float newDim = squareImage.size.width;
    if(newDim != 320.0){
        CGSize finalSize = CGSizeMake(320.0, 320.0);
        UIGraphicsBeginImageContext(finalSize);
        [squareImage drawInRect:CGRectMake(0, 0, finalSize.width, finalSize.height)];
        playImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
    }else{
        playImage = squareImage;
    }
}

finalImage = [playImage CGImage];
tileImgArray = [NSMutableArray arrayWithCapacity:0];
for(int i = 0; i < 16; i++){
    r = i/4;
    c = i%4;
    //*
    tmp = CGImageCreateWithImageInRect(finalImage, CGRectMake(c*tileSize, r*tileSize, tileSize, tileSize));
    [tileImgArray addObject:[UIImage imageWithCGImage:tmp]];
}

当原始(可变图像)的较小尺寸大于或小于320像素时,代码可正常工作.当它恰好是320时,得到的80x80图像几乎全部是黑色的,有些像素边缘可能(我无法分辨)可能来自原始图像.

我通过直接显示完整图像进行测试:

[UIImage imageWithCGImage:finalImage];

间接地:

[UIImage imageWithCGImage:CGImageCreateWithImageInRect(finalImage, CGRectMake(0, 0, 320, 320))];

在这两种情况下,显示都有效.只有当我试图切出图像的某些部分时才会出现问题.

经过一些更多的实验,我发现了以下解决方案(我仍然不知道为什么它不像最初编写的那样工作.)但是无论如何,即使在不需要调整大小的情况下,调整大小代码之后的切片也会起作用:

if(newDim != 320.0){
            CGSize finalSize = CGSizeMake(320.0, 320.0);
            UIGraphicsBeginImageContext(finalSize);
            [squareImage drawInRect:CGRectMake(0, 0, finalSize.width, finalSize.height)];
            playImage = UIGraphicsGetImageFromCurrentImageContext();
            UIGraphicsEndImageContext();
}else{
            CGSize finalSize = CGSizeMake(320.0, 320.0);
            UIGraphicsBeginImageContext(finalSize);
            [squareImage drawInRect:CGRectMake(0, 0, finalSize.width, finalSize.height)];
            playImage = UIGraphicsGetImageFromCurrentImageContext();
            UIGraphicsEndImageContext();
}

任何人都有任何线索为什么会这样？

PS是的,如果此处不再需要/ else.然而,在我知道它将起作用之前删除它将是愚蠢的.