Suppose you have hundreds or even thousands of photos that you want to present on a web page. If the images use the original camera resolution, they could severely slow down or even paralyze a website populated with this data. Optimizing the images can save bandwidth on the network and space on the storage medium.

With a large number of images, a batch processing tool such as imgp [1] comes in handy. The command-line tool, formerly known as imgd and written in Python, provides functions for resizing images in JPEG and PNG formats, as well as converting from PNG to JPEG, rotating the images, and removing metadata.

Even with thousands of files, imgp does its job at lightning speed. The developer, Arun Prakash Jana, achieves this through multicore processing, an adaptive algorithm, and the Python Pillow library [2].

On processors that support single instruction, multiple data (SIMD) [3], you can use Pillow-SIMD [4] as an alternative to further speed up processing. In testing on an external hard disk with a USB 2 connection, Jana claims to have converted 8,823 images of different resolutions (with a total size of 4.5GB) to a resolution of 1366x1000 pixels in about eight minutes, with the resulting total size dropping to 897MB.

Easy Access

To install imgp on a current distribution, you can simply use the package manager in most cases. The current version 2.8 is available on Arch Linux, CentOS, Debian Testing and Unstable, Devuan, Fedora, openSUSE Leap 15.3, Ubuntu 21.04, and others.

If your distribution ships with an older version of imgp, install the packages from GitHub for DEB and RPM-based distributions or build the package from the source code [5]. Python 3.5 or newer is required. The nnn [6] terminal file manager, also developed by Jana, offers batch conversion using imgp as a script. (Jana is also the developer of another useful tool, googler [7]).

Using imgp's options, you can resize image files by specifying a percentage or a resolution. You can also rotate the image clockwise by a freely selectable angle, optimize images to save space, convert PNG to JPEG, delete Exif metadata, and more.

Options

To test out imgp's capabilities, we tried out various imgp command-line options on 65 vacation photos taken with a smartphone. The image sizes ranged from around 2 to 5MB, with a total size of 215.7MB. The tests were run on a PC with a Ryzen 7 3700X CPU with 32GB RAM.

If you enter imgp at the command line without specifying any other parameters, the help page (Figure 1) loads with a list of all the options for manipulating the size or orientation of an image. As usual, imgp assumes the current directory as the source unless you specify a different source. However, you can also process multiple sources in a single command.

Figure 1: To access the help page, enter imgp without any other parameters. The options listed on the help page include all the common functions for image manipulation.

Amazingly Fast

As the simplest test case, we entered the following command

imgp -x 1024x768

in the directory containing the 65 image files. This command converts all the images (with various resolutions) to 1024x768 pixels. The entire process took 1.29 seconds in the test and reduced the folder size from 215.1MB to 8.4MB (Figure 2). Listing 1 shows the command structure for processing multiple folders and files simultaneously.

imgp -x 1024x768 ~/images/image1 ~/photos/image2 ~/pictures/

Figure 2: In the simplest case, you just specify the desired resolution. The software converts the images in a very short time.