Merge pull request #16889 from mehlukas:3.4-consolidateImshow

* consolidate tutorials on image read/display/write * fix unsused variables * apply requested changes * apply requested changes * fix mistake
2026-07-30 07:43:03 +04:00 · 2020-04-07 16:14:51 +02:00
parent 734771418e
commit 75bd9f86b2
11 changed files with 118 additions and 352 deletions
@@ -1,153 +1,4 @@
 Getting Started with Images {#tutorial_py_image_display}
 ===========================

-Goals
-----
-
-   Here, you will learn how to read an image, how to display it, and how to save it back
-   You will learn these functions : **cv.imread()**, **cv.imshow()** , **cv.imwrite()**
-   Optionally, you will learn how to display images with Matplotlib
-
-Using OpenCV
------------
-
-### Read an image
-
-Use the function **cv.imread()** to read an image. The image should be in the working directory or
-a full path of image should be given.
-
-Second argument is a flag which specifies the way image should be read.
-
-   cv.IMREAD_COLOR : Loads a color image. Any transparency of image will be neglected. It is the
-    default flag.
-   cv.IMREAD_GRAYSCALE : Loads image in grayscale mode
-   cv.IMREAD_UNCHANGED : Loads image as such including alpha channel
-
-@note Instead of these three flags, you can simply pass integers 1, 0 or -1 respectively.
-
-See the code below:
-@code{.py}
-import numpy as np
-import cv2 as cv
-
-# Load a color image in grayscale
-img = cv.imread('messi5.jpg',0)
-@endcode
-
-**warning**
-
-Even if the image path is wrong, it won't throw any error, but `print img` will give you `None`
-
-### Display an image
-
-Use the function **cv.imshow()** to display an image in a window. The window automatically fits to
-the image size.
-
-First argument is a window name which is a string. Second argument is our image. You can create as
-many windows as you wish, but with different window names.
-@code{.py}
-cv.imshow('image',img)
-cv.waitKey(0)
-cv.destroyAllWindows()
-@endcode
-A screenshot of the window will look like this (in Fedora-Gnome machine):
-
-![image](images/opencv_screenshot.jpg)
-
-**cv.waitKey()** is a keyboard binding function. Its argument is the time in milliseconds. The
-function waits for specified milliseconds for any keyboard event. If you press any key in that time,
-the program continues. If **0** is passed, it waits indefinitely for a key stroke. It can also be
-set to detect specific key strokes like, if key a is pressed etc which we will discuss below.
-
-@note Besides binding keyboard events this function also processes many other GUI events, so you
-MUST use it to actually display the image.
-
-**cv.destroyAllWindows()** simply destroys all the windows we created. If you want to destroy any
-specific window, use the function **cv.destroyWindow()** where you pass the exact window name as
-the argument.
-
-@note There is a special case where you can create an empty window and load an image to it later. In
-that case, you can specify whether the window is resizable or not. It is done with the function
-**cv.namedWindow()**. By default, the flag is cv.WINDOW_AUTOSIZE. But if you specify the flag to be
-cv.WINDOW_NORMAL, you can resize window. It will be helpful when an image is too large in dimension
-and when adding track bars to windows.
-
-See the code below:
-@code{.py}
-cv.namedWindow('image', cv.WINDOW_NORMAL)
-cv.imshow('image',img)
-cv.waitKey(0)
-cv.destroyAllWindows()
-@endcode
-### Write an image
-
-Use the function **cv.imwrite()** to save an image.
-
-First argument is the file name, second argument is the image you want to save.
-@code{.py}
-cv.imwrite('messigray.png',img)
-@endcode
-This will save the image in PNG format in the working directory.
-
-### Sum it up
-
-Below program loads an image in grayscale, displays it, saves the image if you press 's' and exit, or
-simply exits without saving if you press ESC key.
-@code{.py}
-import numpy as np
-import cv2 as cv
-
-img = cv.imread('messi5.jpg',0)
-cv.imshow('image',img)
-k = cv.waitKey(0)
-if k == 27:         # wait for ESC key to exit
-    cv.destroyAllWindows()
-elif k == ord('s'): # wait for 's' key to save and exit
-    cv.imwrite('messigray.png',img)
-    cv.destroyAllWindows()
-@endcode
-
-**warning**
-
-If you are using a 64-bit machine, you will have to modify `k = cv.waitKey(0)` line as follows :
-`k = cv.waitKey(0) & 0xFF`
-
-Using Matplotlib
----------------
-
-Matplotlib is a plotting library for Python which gives you wide variety of plotting methods. You
-will see them in coming articles. Here, you will learn how to display image with Matplotlib. You can
-zoom images, save them, etc, using Matplotlib.
-@code{.py}
-import numpy as np
-import cv2 as cv
-from matplotlib import pyplot as plt
-
-img = cv.imread('messi5.jpg',0)
-plt.imshow(img, cmap = 'gray', interpolation = 'bicubic')
-plt.xticks([]), plt.yticks([])  # to hide tick values on X and Y axis
-plt.show()
-@endcode
-A screen-shot of the window will look like this :
-
-![image](images/matplotlib_screenshot.jpg)
-
-@note Plenty of plotting options are available in Matplotlib. Please refer to Matplotlib docs for more
-details. Some, we will see on the way.
-
-__warning__
-
-Color image loaded by OpenCV is in BGR mode. But Matplotlib displays in RGB mode. So color images
-will not be displayed correctly in Matplotlib if image is read with OpenCV. Please see the exercises
-for more details.
-
-Additional Resources
--------------------
-
-#  [Matplotlib Plotting Styles and Features](http://matplotlib.org/api/pyplot_api.html)
-
-Exercises
---------
-
-#  There is some problem when you try to load color image in OpenCV and display it in Matplotlib.
-    Read [this discussion](http://stackoverflow.com/a/15074748/1134940) and understand it.
+Tutorial content has been moved: @ref tutorial_display_image
@@ -1,7 +1,7 @@
 Gui Features in OpenCV {#tutorial_py_table_of_contents_gui}
 ======================

-   @subpage tutorial_py_image_display
+-   @ref tutorial_display_image

    Learn to load an
    image, display it, and save it back