init - 初始化项目

doc/js_tutorials/js_imgproc/js_pyramids/js_pyramids.markdown

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+Image Pyramids {#tutorial_js_pyramids}
+==============
+
+Goal
+----
+
+-   We will learn about Image Pyramids
+-   We will learn these functions: **cv.pyrUp()**, **cv.pyrDown()**
+
+Theory
+------
+
+Normally, we used to work with an image of constant size. But on some occasions, we need to work
+with (the same) images in different resolution. For example, while searching for something in
+an image, like face, we are not sure at what size the object will be present in said image. In that
+case, we will need to create a set of the same image with different resolutions and search for object
+in all of them. These set of images with different resolutions are called **Image Pyramids** (because
+when they are kept in a stack with the highest resolution image at the bottom and the lowest resolution
+image at top, it looks like a pyramid).
+
+There are two kinds of Image Pyramids. 1) **Gaussian Pyramid** and 2) **Laplacian Pyramids**
+
+Higher level (Low resolution) in a Gaussian Pyramid is formed by removing consecutive rows and
+columns in Lower level (higher resolution) image. Then each pixel in higher level is formed by the
+contribution from 5 pixels in underlying level with gaussian weights. By doing so, a \f$M \times N\f$
+image becomes \f$M/2 \times N/2\f$ image. So area reduces to one-fourth of original area. It is called
+an Octave. The same pattern continues as we go upper in pyramid (ie, resolution decreases).
+Similarly while expanding, area becomes 4 times in each level. We can find Gaussian pyramids using
+**cv.pyrDown()** and **cv.pyrUp()** functions.
+
+Laplacian Pyramids are formed from the Gaussian Pyramids. There is no exclusive function for that.
+Laplacian pyramid images are like edge images only. Most of its elements are zeros. They are used in
+image compression. A level in Laplacian Pyramid is formed by the difference between that level in
+Gaussian Pyramid and expanded version of its upper level in Gaussian Pyramid.
+
+Downsample
+------
+
+We use the function: **cv.pyrDown (src, dst, dstsize = new cv.Size(0, 0), borderType  = cv.BORDER_DEFAULT)**
+@param src         input image.
+@param dst         output image; it has the specified size and the same type as src.
+@param dstsize     size of the output image.
+@param borderType  pixel extrapolation method(see cv.BorderTypes, cv.BORDER_CONSTANT isn't supported).
+
+Try it
+------
+
+\htmlonly
+<iframe src="../../js_pyramids_pyrDown.html" width="100%"
+        onload="this.style.height=this.contentDocument.body.scrollHeight +'px';">
+</iframe>
+\endhtmlonly
+
+Upsample
+------
+
+We use the function: **cv.pyrUp (src, dst, dstsize = new cv.Size(0, 0), borderType  = cv.BORDER_DEFAULT)**
+@param src         input image.
+@param dst         output image; it has the specified size and the same type as src.
+@param dstsize     size of the output image.
+@param borderType  pixel extrapolation method(see cv.BorderTypes, only cv.BORDER_DEFAULT is supported).
+
+Try it
+------
+
+\htmlonly
+<iframe src="../../js_pyramids_pyrUp.html" width="100%"
+        onload="this.style.height=this.contentDocument.body.scrollHeight +'px';">
+</iframe>
+\endhtmlonly