图像已调整大小错误：CGBitmapContextCreate：不支持的参数 [英] Image resized error: CGBitmapContextCreate: unsupported parameter

问题描述

我使用以下代码（来自博客文章）来调整图片大小

I am using the following code (from a blog post) to resize an image

if (inImage.size.width <= inImage.size.height) {
    // Portrait
    ratio = inImage.size.height / inImage.size.width;
    resizedRect = CGRectMake(0, 0, width, width * ratio);
}
else {
    // Landscape
    ratio = inImage.size.width / inImage.size.height;
    resizedRect = CGRectMake(0, 0, height * ratio, height);
}

CGImageRef          imageRef = [inImage CGImage];
CGImageAlphaInfo    alphaInfo = CGImageGetAlphaInfo(imageRef);

if (alphaInfo == kCGImageAlphaNone)
    alphaInfo = kCGImageAlphaNoneSkipLast;

CGContextRef bitmap = CGBitmapContextCreate(
                                            NULL,
                                            resizedRect.size.width,     // width
                                            resizedRect.size.height,        // height
                                            CGImageGetBitsPerComponent(imageRef),   // really needs to always be 8
                                            4 * resizedRect.size.width, // rowbytes
                                            CGImageGetColorSpace(imageRef),
                                            alphaInfo
                                            );

但由于某种原因，我会尝试调整大小，因此会产生以下错误

but for some reason depending on the size I am try to resize to I get the following error generated

CGBitmapContextCreate：unsupported
参数组合：8整数
bits / component; 32位/像素;
3分量色彩空间;
kCGImageAlphaNoneSkipFirst; XXX
bytes / row。

CGBitmapContextCreate: unsupported parameter combination: 8 integer bits/component; 32 bits/pixel; 3-component colorspace; kCGImageAlphaNoneSkipFirst; XXX bytes/row.

其中XXX因图像而异。

where XXX differs depending on which image.

我正在创建的矩形是图像的比例，我从宽度/高度（取决于方面）和多个目标宽度/高度的比率。

The rect I am creating is propotional to the image, I take a ratio from the width/height (depending on aspect) and multiple that be target width/height.

以下是一些示例（X错误，/ doesnt），调整大小将为50xX或Xx50，具体取决于方面：

Here are some examples (X errors, / doesnt), the resize size will be 50xX or Xx50 depending on aspect:

Source   50x50   69x69
430x320  /      X
240x320  /      /
272x320  /      /
480x419  /      X
426x320  X      X
480x256  X      X

推荐答案

你写的地方 thumbRect ，你的意思是 resizedRect ？ thumbRect 否则不会发生。

Where you wrote thumbRect, did you mean resizedRect? thumbRect does not otherwise occur.

我怀疑问题是 resizedRect.size。 width 是非整数。请注意，它是浮点数。

I suspect the problem is that resizedRect.size.width is non integral. Note that it's floating point.

CGBitmapContextCreate 的width和bytesPerRow参数被声明为整数。传递浮点值（例如此处）时，它会被截断。

The width and bytesPerRow parameters of CGBitmapContextCreate are declared as integers. When you pass a floating point value, such as here, it gets truncated.

假设你的resizedRect.size.width是1.25。然后你最终会传递1作为宽度，而floor（1.25 * 4）== 5作为每行的字节数。这是不一致的。对于每行字节的宽度，你总是希望传递四次。

Suppose your resizedRect.size.width is 1.25. Then you will end up passing 1 for the width, and floor(1.25 * 4) == 5 as the bytes per row. That's inconsistent. You always want to pass four times whatever you passed for the width for the bytes per row.

顺便说一句，你也可以将bytesPerRow保留为0。然后系统选择最好的bytesPerRow（通常大于宽度的4倍 - 它填充对齐）。

You can also just leave bytesPerRow as 0, by the way. Then the system picks the best bytesPerRow (which is often larger than 4 times the width - it pads out for alignment).

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