处理图像时的步幅和缓冲区大小 [英] Stride and buffersize when processing images

问题描述

在MSDN上，我发现 （用于定义图像步幅）。简而言之，它是缓冲区中一行的宽度（以字节为单位）。

On MSDN I found this for the definition of the image stride. In short it is the width in bytes of one line in the buffer.

现在我在类似的缓冲区中有一个RGB图像，并且获得了步幅和图像宽度（以像素为单位），我想知道那里有多少填充字节已添加。

Now I have an RGB image in a similar buffer and I have been given the stride and the image width in pixels, and I want to know how much padding bytes there have been added.

这是简单的大步吗-3 *图像宽度，因为每个像素有3个字节（RGB）？

Is this simply stride - 3 * imagewidth since I have 3 bytes (RGB) per pixel?

unsafe private void setPrevFrame(IntPtr pBuffer)
    {
        prevFrame = new byte[m_videoWidth, m_videoHeight, 3];
        Byte* b = (byte*) pBuffer;
        for (int i = 0; i < m_videoWidth; i++)
        {
            for (int j = 0; j < m_videoHeight; j++)
            {
                for (int k = 0; k < 3; k++)
                {
                    prevFrame[i,j,k] = *b;
                    b++;
                }
            }
            b += (m_stride - 3 * m_videoHeight);
        }
    }

这是我不确定的最后一行代码大约

It's the last line of code I'm not sure about

推荐答案

跨度将被填充到4字节边界：

Stride will be padded to a 4 byte boundary:

因此，如果您的图像宽度为 W 并且每个像素为3个字节：

So if your image width is W and it is 3 bytes per pixel:

int strideWidth = ((W * 3) - 1) / 4 * 4 + 4; 
//or simply
int strideWidth = Math.Abs(bData.Stride);

//and so
int padding = strideWidth - W * 3;

如果您使用的是 .Stride BitmapData 对象的属性，则必须 Abs 该值，因为它可能为负。

If you are using the .Stride property of the BitmapData object, you must Abs that value because it may be negative.

对问题的编辑之后：

您无需知道填充就可以迭代图像的所有字节：

There is no need for you to know the padding in order to iterate all the bytes of the image:

unsafe private void setPrevFrame(IntPtr pBuffer)
{
    for (int j = 0; j < m_videoHeight; j++)
    {
        b = scan0 + j * stride; //the first byte of the first pixel of the row
        for (int i = 0; i < m_videoWidth; i++)
        {
           ...
        }
    }
}

如前所述，您以前的方法在自下而上的图像上也会失败在您发布的MSDN链接中。

Your previous method will also fail on bottom-up images, as described in the MSDN link you posted.

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