如何使用 OpenCV2.0 和 Python2.6 调整图像大小

How to resize an image with OpenCV2.0 and Python2.6

提问by Bastian

I want to use OpenCV2.0 and Python2.6 to show resized images. I used and adopted the example at http://opencv.willowgarage.com/documentation/python/cookbook.htmlbut unfortunately this code is for OpenCV2.1 and seem not to be working on 2.0. Here my code:

我想使用 OpenCV2.0 和 Python2.6 来显示调整大小的图像。我使用并采用了http://opencv.willowgarage.com/documentation/python/cookbook.html 上的示例，但不幸的是，此代码适用于 OpenCV2.1，似乎不适用于 2.0。这是我的代码：

import os, glob
import cv

ulpath = "exampleshq/"

for infile in glob.glob( os.path.join(ulpath, "*.jpg") ):
    im = cv.LoadImage(infile)
    thumbnail = cv.CreateMat(im.rows/10, im.cols/10, cv.CV_8UC3)
    cv.Resize(im, thumbnail)
    cv.NamedWindow(infile)
    cv.ShowImage(infile, thumbnail)
    cv.WaitKey(0)
    cv.DestroyWindow(name)

Since I cannot use

由于我无法使用

cv.LoadImageM

I used

我用了

cv.LoadImage

instead, which was no problem in other applications. Nevertheless cv.iplimage has no attribute rows, cols or size. Can anyone give me a hint, how to solve this problem? Thanks.

相反，这在其他应用程序中没有问题。然而 cv.iplimage 没有属性行、列数或大小。谁能给我一个提示，如何解决这个问题？谢谢。

回答by jlengrand

You could use the GetSize function to get those information, cv.GetSize(im) would return a tuple with the width and height of the image. You can also use im.depth and img.nChan to get some more information.

您可以使用 GetSize 函数来获取这些信息， cv.GetSize(im) 将返回一个包含图像宽度和高度的元组。您还可以使用 im.depth 和 img.nChan 来获取更多信息。

And to resize an image, I would use a slightly different process, with another image instead of a matrix. It is better to try to work with the same type of data:

并且要调整图像大小，我会使用稍微不同的过程，使用另一个图像而不是矩阵。最好尝试使用相同类型的数据：

size = cv.GetSize(im)
thumbnail = cv.CreateImage( ( size[0] / 10, size[1] / 10), im.depth, im.nChannels)
cv.Resize(im, thumbnail)

Hope this helps ;)

希望这可以帮助 ;）

Julien

于连

回答by emem

If you wish to use CV2, you need to use the resizefunction.

如果您想使用 CV2，则需要使用该resize功能。

For example, this will resize both axes by half:

例如，这会将两个轴的大小减半：

small = cv2.resize(image, (0,0), fx=0.5, fy=0.5) 

and this will resize the image to have 100 cols (width) and 50 rows (height):

这将调整图像大小，使其具有 100 列（宽度）和 50 行（高度）：

resized_image = cv2.resize(image, (100, 50)) 

Another option is to use scipymodule, by using:

另一种选择是使用scipy模块，通过使用：

small = scipy.misc.imresize(image, 0.5)

There are obviously more options you can read in the documentation of those functions (cv2.resize, scipy.misc.imresize).

显然，您可以在这些函数的文档（cv2.resize、scipy.misc.imresize）中阅读更多选项。

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Update:
According to the SciPy documentation:

更新：
根据SciPy 文档：

imresizeis deprecatedin SciPy 1.0.0, and will be removed in 1.2.0.
Use skimage.transform.resizeinstead.

imresize被弃用的SciPy的1.0.0，并且将在1.2.0被删除。
使用skimage.transform.resize来代替。

Note that if you're looking to resize by a factor, you may actually want skimage.transform.rescale.

请注意，如果您希望按因子调整大小，您实际上可能需要skimage.transform.rescale.

回答by Jo?o Cartucho

Example doubling the image size

将图像大小加倍的示例

There are two ways to resize an image. The new size can be specified:

有两种方法可以调整图像大小。可以指定新的大小：

1. Manually;

   height, width = src.shape[:2]

   dst = cv2.resize(src, (2*width, 2*height), interpolation = cv2.INTER_CUBIC)

2. By a scaling factor.

   dst = cv2.resize(src, None, fx = 2, fy = 2, interpolation = cv2.INTER_CUBIC), where fxis the scaling factor along the horizontal axis and fyalong the vertical axis.

1. 手动；

   height, width = src.shape[:2]

   dst = cv2.resize(src, (2*width, 2*height), interpolation = cv2.INTER_CUBIC)

2. 通过比例因子。

   dst = cv2.resize(src, None, fx = 2, fy = 2, interpolation = cv2.INTER_CUBIC)，其中fx是沿水平轴的缩放因子，fy 是沿垂直轴的缩放因子。

To shrink an image, it will generally look best with INTER_AREA interpolation, whereas to enlarge an image, it will generally look best with INTER_CUBIC (slow) or INTER_LINEAR (faster but still looks OK).

要缩小图像，通常使用 INTER_AREA 插值看起来最好，而要放大图像，通常使用 INTER_CUBIC（慢）或 INTER_LINEAR（更快但看起来仍然可以）看起来最好。

Example shrink image to fit a max height/width (keeping aspect ratio)

示例缩小图像以适应最大高度/宽度（保持纵横比）

import cv2

img = cv2.imread('YOUR_PATH_TO_IMG')

height, width = img.shape[:2]
max_height = 300
max_width = 300

# only shrink if img is bigger than required
if max_height < height or max_width < width:
    # get scaling factor
    scaling_factor = max_height / float(height)
    if max_width/float(width) < scaling_factor:
        scaling_factor = max_width / float(width)
    # resize image
    img = cv2.resize(img, None, fx=scaling_factor, fy=scaling_factor, interpolation=cv2.INTER_AREA)

cv2.imshow("Shrinked image", img)
key = cv2.waitKey()

Using your code with cv2

在 cv2 中使用您的代码

import cv2 as cv

im = cv.imread(path)

height, width = im.shape[:2]

thumbnail = cv.resize(im, (round(width / 10), round(height / 10)), interpolation=cv.INTER_AREA)

cv.imshow('exampleshq', thumbnail)
cv.waitKey(0)
cv.destroyAllWindows()

回答by AndyP

def rescale_by_height(image, target_height, method=cv2.INTER_LANCZOS4):
    """Rescale `image` to `target_height` (preserving aspect ratio)."""
    w = int(round(target_height * image.shape[1] / image.shape[0]))
    return cv2.resize(image, (w, target_height), interpolation=method)

def rescale_by_width(image, target_width, method=cv2.INTER_LANCZOS4):
    """Rescale `image` to `target_width` (preserving aspect ratio)."""
    h = int(round(target_width * image.shape[0] / image.shape[1]))
    return cv2.resize(image, (target_width, h), interpolation=method)

回答by nathancy

Here's a function to upscale or downscale an image by desired width or height while maintaining aspect ratio

这是一个按所需宽度或高度放大或缩小图像同时保持纵横比的功能

# Resizes a image and maintains aspect ratio
def maintain_aspect_ratio_resize(image, width=None, height=None, inter=cv2.INTER_AREA):
    # Grab the image size and initialize dimensions
    dim = None
    (h, w) = image.shape[:2]

    # Return original image if no need to resize
    if width is None and height is None:
        return image

    # We are resizing height if width is none
    if width is None:
        # Calculate the ratio of the height and construct the dimensions
        r = height / float(h)
        dim = (int(w * r), height)
    # We are resizing width if height is none
    else:
        # Calculate the ratio of the width and construct the dimensions
        r = width / float(w)
        dim = (width, int(h * r))

    # Return the resized image
    return cv2.resize(image, dim, interpolation=inter)

Usage

用法

import cv2

image = cv2.imread('1.png')
cv2.imshow('width_100', maintain_aspect_ratio_resize(image, width=100))
cv2.imshow('width_300', maintain_aspect_ratio_resize(image, width=300))
cv2.waitKey()

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Using this example image

使用此示例图像

Simply downscale to width=100(left) or upscale to width=300(right)

只需缩小到width=100（左）或放大到width=300（右）