如何正确处理内存驻留位图调整大小

I have bitmap residing in memory (coming from my webcam but I don't think that this makes a difference. It is 960x540 120dpi

我有位图驻留在内存中（来自我的网络摄像头，但我不认为这有所不同。它是960x540 120dpi

you see that the picture in the lower part gets till the point where my shirt begins.

你看到下半部分的图片一直到我的衬衫开始的地方。

I know the bmp dimensions since I put this code prior resize

我知道bmp尺寸因为我在调整大小之前放了这个代码

using (var fileStream = new FileStream(@"C:\temp\3.bmp", FileMode.Create))
{
    BitmapEncoder encoder = new PngBitmapEncoder();
    encoder.Frames.Add(BitmapFrame.Create(source));
    encoder.Save(fileStream);
}

and the result is the picture above.

结果如上图所示。

Then I resize it with that:

然后我用它调整大小：

var resizedImage = new RenderTargetBitmap(
                width, height,           // Resized dimensions 200x112
                source.DpiX, source.DpiY,// Default DPI values
                PixelFormats.Default);   // Default pixel format

and the result is the bmp below which is properly 200x112 but it cuts out in part of the image in the lower and right part.

结果是下面的bmp恰好是200x112，但它在部分图像的下部和右部切出。

I have seen that the problem is related with the dpi value in the RenderTargetBitmap instruction. If I divide the dpi by 1.25 everything gets fine but why 1.25???????

我已经看到问题与RenderTargetBitmap指令中的dpi值有关。如果我将dpi除以1.25，一切都会好起来，但为什么1.25 ???????

Thank you in advance for any help Patrick

提前感谢Patrick的任何帮助

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There is something additional that I can't understand: I know the initial bitmap size for I have saved it to filesytem with the instructions above. But if I look at the properties by putting a breakpoint I see:

还有一些我无法理解的内容：我知道我的初始位图大小已经按照上面的说明将它保存到filesytem。但如果我通过设置断点来查看属性，我会看到：

BITMAP BEFORE RESIZE

BITMAP在调整之前

width,height = 768, 432

宽度，高度= 768,432

pixelwidth, pixelheight = 960, 540

pixelwidth，pixelheight = 960,540

dpiX, dpiY= 120, 120

dpiX，dpiY = 120,120

BITMAP AFTER RESIZE

BITMAP重新调整后

width,height = 160, 89

宽度，高度= 160,89

pixelwidth, pixelheight = 200, 112

pixelwidth，pixelheight = 200,112

dpiX, dpiY= 120, 120

dpiX，dpiY = 120,120

now I know that what counts here is pixelwidth, pixelheight so that's correct.

现在我知道这里重要的是像素宽度，像素高度，这是正确的。

If I do 960/786 I get 1.25! So that's my number but why? Can I correct the code as to make it a general solution???

如果我做960/786，我得到1.25！这是我的号码，但为什么呢？我可以更正代码，使其成为一般解决方案吗？

1 个解决方案

#1

Instead of a RenderTargetBitmap you should simply use a TransformedBitmap with an appropriate ScaleTransform:

您应该使用具有适当ScaleTransform的TransformedBitmap而不是RenderTargetBitmap：

var scale = 200d / 960d;
var resizedImage = new TransformedBitmap(source, new ScaleTransform(scale, scale));