Technology Trekking

Image cropping is very easy using python library Pillow. Following is simple program to crop image in required parts.

Most important part of cropping is to know pixel size of your image, you can crop required portion using .crop method of Image module of Pillow.

Sample program

Please note that crop takes tuple  having four values as input. These four values represent left, upper, right, lower point .

Original image

Left Half of the image

Right Half of the image

Top Right corner of the image

Here is the output of the program, please note the pixel size of each cropped image.

$ python3.6 06_crop_image_01.py 
*** Program Started ***
im.size (1920, 1318)
im.size (960, 1318)
im.size (960, 1318)
im.size (960, 659)
*** Program Ended ***

Python Library Pillow can be used very effectively to compress images. While doing some research on this I found that .JPG files can be compress very effectively however this does not work well with .PNG files. Here is sample program to reduce file size of an image.

Output of the program while using .JPG file as input and output

$ python3.6 05_compress_image_01.py 
*** Program Started ***
Input file size : (5456, 3632)
Input file name : 05_compress_image_01_input.jpg
Input Image Size : 1611664
Output file size : (5456, 3632)
Output file name : 05_compress_image_01_output.jpg
Output Image Size : 443479
*** Program Ended ***

Output of the program while using .PNG files as input and output

$ python3.6 05_compress_image_01.py 
*** Program Started ***
Input file size : (1920, 1282)
Input file name : 05_compress_image_01_input.png
Input Image Size : 3683320
Output file size : (1920, 1282)
Output file name : 05_compress_image_01_output.png
Output Image Size : 3619363
*** Program Ended ***

As you can see, while using .PNG files for input and output, there is hardly any change in file size however when you used .JPG files, output files is of 27% of original file size. Your percentage reduction might be different based on the file that you have used.

Please note input and out file dimensions, number of pixels stays the same.

Python library Pillow can be used to resize images. Please note resize does not mean compressing image. Yes, reducing pixels can lead to reduction in file size in terms of KBs however it will not be significant. If you need to compress image, please check How to compress image using python.

While resizing the image file, you need to maintain the aspect ration, else image might get distorted, we will see an example of the same.

Here is sample program to resize.

here is the output

$ python3.6 04_resize_image_01.py 
*** Program Started ***
im.size (1920, 1318)
im.size (960, 659)
*** Program Ended ***

Here we have maintained the aspect ratio so the files will look similar
Input

Output

Now lets look at resize by not maintaining the aspect ratio

Output of the program

$ python3.6 04_resize_image_02.py 
*** Program Started ***
im.size (1920, 1318)
im.size (500, 480)
*** Program Ended ***

You can see the issue with changing of aspect ratio.

Input

Output

Size comparison 

As a part of image processing, we sometimes need to write text on the image file. Pillow is a python library which can be used to add text on images using python. Using Pillow, which us a fork of PIL, is very easy for these kind of image processing activities.

Let us have a look at adding simple text on image file.

Please note that text location is determined by parameter position, its tuple with two parameters and it represents x and y axis position. In below example I have used position = (50, 50).

Now if you are wondering what these values represent, these are pixel numbers with (0,0) being top left corner.  If you image size is (640, 480) and you want to put any character exactly at center, you need to provide position as (320,240). Hope this clarifies the parameter

Here is the output

As you can see the text added does not look good sine we have not added any formatting to text.  Now let us look at formatted text  on image. Here is program with additional parameters for font

Here we have added two additional parameters, font and color, you can plan your desired font into font directory and can use it for adding text to image file.

Note: I tried using this for non english text e.g. devnagari text but it did not work.

Here is the output.

Sometimes we need a blank image file to be created during execution of program, during processing required text or anything else can be added. Following is the sample program to create blank file using PIL, python.

You can decide file size and color as per your requirement.

Here is the output image