How to resize an image with OpenCV2 0 and Python2 6

Question

I want to use OpenCV2 0 and Python2 6 to show resized images  I used and adopted this example but unfortunately  this code is for OpenCV2 1 and does not seem to be working on 2 0  Here my code  import os  glob import cv  ulpath    quot exampleshq  quot   for infile in glob glob  os path join ulpath   quot   jpg quot          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 cv LoadImageM  I used 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

User · Answer

Example doubling the image size

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

Manually;

height, width = src.shape[:2]

dst = cv2.resize(src, (2*width, 2*height), interpolation = cv2.INTER_CUBIC)
By a scaling factor.

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

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).

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

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

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()

User · Answer

If you wish to use CV2  you need to use the resize function   For example  this will resize both axes by half   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    resized image   cv2 resize image   100  50      Another option is to use scipy module  by using   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      Update  According to the SciPy documentation      imresize is deprecated in SciPy 1 0 0  and   will be removed in 1 2 0  Use skimage transform resize instead    Note that if you re looking to resize by a factor  you may actually want skimage transform rescale

User · Answer

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

User · Answer

Here s a function to upscale or downscale an image by desired width or height while maintaining aspect ratio    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  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       Using this example image    Simply downscale to width 100  left  or upscale to width 300  right

User · Answer

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    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   size   cv GetSize im  thumbnail   cv CreateImage    size 0    10  size 1    10   im depth  im nChannels  cv Resize im  thumbnail    Hope this helps     Julien

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

Example doubling the image size

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

Using your code with cv2

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