Python Program to Find the Size (Resolution) of a Image

You will learn to find resolution of a jpeg image in this example without using external libraries
What is image resolution?

To understand this example, you should have the knowledge of following Python programming topics:

JPEG (pronounced "jay-peg") stands for Joint Photographic Experts Group. It is one of the most widely used compression techniques for image compression.

Most of the file formats have headers (initial few bytes) which contain useful information about the file.

For example, jpeg headers contain information like height, width, number of color (grayscale or RGB) etc. In this program, we find the resolution of a jpeg image reading these headers, without using any external library.

Source Code of Find Resolution of JPEG Image

def jpeg_res(filename):
   """"This function prints the resolution of the jpeg image file passed into it"""

   # open image for reading in binary mode
   with open(filename,'rb') as img_file:

       # height of image (in 2 bytes) is at 164th position
       img_file.seek(163)

       # read the 2 bytes
       a = img_file.read(2)

       # calculate height
       height = (a[0] << 8) + a[1]

       # next 2 bytes is width
       a = img_file.read(2)

       # calculate width
       width = (a[0] << 8) + a[1]

   print("The resolution of the image is",width,"x",height)

jpeg_res("img1.jpg")

Output

The resolution of the image is 280 x 280

In this program, we opened the image in binary mode. Non-text files must be open in this mode. The height of the image is at 164th position followed by width of the image. Both are 2 bytes long.

Note that this is true only for JPEG File Interchange Format (JFIF) standard. If your image is encode using other standard (like EXIF), the code will not work.

We convert the 2 bytes into a number using bitwise shifting operator <<. Finally, the resolution is displayed.