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Image Stride（内存图像行跨度）

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When a video image is stored in memory, the memory buffer might contain extra padding bytes after each row of pixels. The padding bytes affect how the image is store in memory, but do not affect how the image is displayed.

当视频图像存储在内存时，图像的每一行末尾也许包含一些扩展的内容，这些扩展的内容只影响图像如何存储在内存中，但是不影响图像如何显示出来；

The stride is the number of bytes from one row of pixels in memory to the next row of pixels in memory. Stride is also called pitch . If padding bytes are present, the stride is wider than the width of the image, as shown in the following illustration.

Stride 就是这些扩展内容的名称，Stride 也被称作 Pitch，如果图像的每一行像素末尾拥有扩展内容，Stride 的值一定大于图像的宽度值，就像下图所示：

Image Stride（内存图像行跨度）

Two buffers that contain video frames with equal dimensions can have two different strides. If you process a video image, you must take into the stride into account.

两个缓冲区包含同样大小（宽度和高度）的视频帧，却不一定拥有同样的 Stride 值，如果你处理一个视频帧，你必须在计算的时候把 Stride 考虑进去；

In addition, there are two ways that an image can be arranged in memory. In a top-down image, the top row of pixels in the image appears first in memory. In a bottom-up image, the last row of pixels appears first in memory. The following illustration shows the difference between a top-down image and a bottom-up image.

另外，一张图像在内存中有两种不同的存储序列（arranged），对于一个从上而下存储（Top-Down）的图像，最顶行的像素保存在内存中最开头的部分，对于一张从下而上存储（Bottom-Up）的图像，最后一行的像素保存在内存中最开头的部分，下面图示展示了这两种情况：

Image Stride（内存图像行跨度）