How can I compress images?

Question

I have 5,000 images which I need to compress (to display on my website).

I am new to Ubuntu. So what do I do?

Answer 1

The "compression" word seems to be misinterpreted in this question, but it's yet valid depending on the context you wish to see this.

The scenery

Let's face that Web designers, Web developers and/or Web masters need to "compress" our image files in order to make them enough "lightweight" to be quickly uploaded to our hosting if we're working directly on a real production environment. Which won't affect if we were working in a local testing production environment.

Many of the answers seems to refer to other things, mostly caused because of -probably- they haven't faced such scenery. That's why I start explaining this.

So. Let's understand what the answer need to solve:

1. The picture MUST be lightweight
2. The picture MUST be "compressed" in order to lose file size but not "rezised" as refered by another user who pointed to a duplicated on this question JPG batch compression & rename (find -exec, xargs, piping?)
3. The pictures should be batch compressed, preferably via a GUI.

Lightweight Picture

Let's first understand what a "lightweight picture" should be.

High Definition Pictures, with resolutions over 1024px may have a big file size. I provide an example on this screenshot:

In the file properties window we can see this is a 9.5 MB file, which will delay a lot to upload and will delay a lot in order to render on screen when published in a website.

Nevertheless, the image size and grid resolution is really useful for a high definition printing. So that's a different scenery which I won't cover in this explanation.

So, how can I use this image in a website, without waiting years in order to upload and waiting some other years in order to show it in my website?

The file should be compressed.

And when we talk about "compression" we explicitly need to change it's quality in order to make it usable for the case we are facing.

So, let's drop the next in a terminal:

convert seminario-tabloide.png test.jpg

This is going to convert the high definition PNG format into a "compressed" JPG format, which by itself is a smaller file! It goes from 9.5 MB to 2.4 MB.

Yet Big?

But, 2.4 MB is yet a big file size. Let's now play with some other ImageMagick convert commands in order to create smaller file sizes:

convert test.jpg -quality 50% test-50p.jpg

This is what we need to do in order to "compress" an image. This is going to reduce the image's quality by 50% and deliver a 938.4 KB <=== (Note: KILOBYTES, not even a Megabyte) filesize.

We can go further and create a smaller file size by adjusting the percentage in the same command via:

convert test.jpg -quality 30% test-30p.jpg

Please have in mind that in this example we're reducing the quality of the file, not the image dimensions. Which will result in a compressed file that it's not visually affected when rendered on screen, but you will see the artifacts when printing in a big paper size (bigger than letter).

Resizing + Compressing = Super Cool!

Now. We can do a different thing. A couple of things indeed: We can first resize the images and apply compression after that, which will result in a smaller file size than the original, and will deliver a useful image for rendering on screen, not so good for printing but it seems we need to display it on screen and not in a printed banner, right?

So let's do this:

convert seminario-tabloide.png -resize 1024x test-1024x.jpg

With this instruction, we are asking the image to be resized to be 1024 pixels wide by any amount of pixels needed in order not to lose aspect ratio.

Now... guess what?

The file size reduced from 9.5 MB to... (suspense music with congas please) 433.7 KILOBYTES

If we wish to maximum compress a maximum compressed file like this, we'll face some overhead data inserted in the file and it will result in a bigger file size. So I won't suggest you to try but if you are expecting me to do the example, ok... Here we go!

convert test-1024x.jpg -quality 50% test-1024x-50p.jpg

And we went from a 433.7 KB to a 176.2 KB in a single command. This example was successful, nevertheless don't expect any exercises to result in smaller file sizes. But you can have lots of fun when running this kind of exercises.

Batch process

Oh! But I almost forget one of the needs: To apply this process to lots of pictures with ease.

For such thing we can do it with two processes.

The terminal

This is faster, and easier. So let's tell the terminal we need to run the same instruction in all the files in a directory, after which I'll explain other instruction.

Convert all to 1024px (you can use any pixels amount)

for i in *; do convert $i -resize 1024x $i-1024x.jpg; done;

Here we're asking the command to run the same instruction for all the files in a directory, apply the transformation and drop a copy with a different name in order to make it easy to select.

Reduce quality by percentage (use any percentage you may wish) to all the pictures in a directory:

for i in *-1024x.jpg; do convert $i -quality 50% $i-50p.jpg; done;

Here we are asking the resized images to be reduced in quality in order to make its filesize smaller.

You can play with these commands and see your results. After a couple of hours having fun you will be an expert.

Nautilus Script

On April 20, 2015 I faced such situation as the original question, so I had to do some research and ask for help on a question. That's why now I know a lot of this. Don't think I borned with this knowledge, man.

If you're not used to terminals and/or wish to use a GUI in order to simply choose your groups of files and apply the transformations, you can create your own Nautilus Actions Script in order to simply right click the group of files and choose an option from the context menu.

For instructions on how to do such thing please read both the question, answer and comments here: How to batch process JPG images to change its quality with Nautilus-Actions?

Good luck!

Answer 2

I use Trimage super simple to use.

only add picture and it compress to install :

sudo apt-get install trimage

Answer 3

The simple way to do it in Ubuntu command line is using ImageMagick.

• Install ImageMagick using the command sudo apt-get install imagemagick
• Navigate to the directory containing the images.
• Run the command mogrify -quality 75% *

Notes:

• The complete list of commands for mogrify can be found here.
• This command will replace the old images. So it is advisable to take a backup, just in case.

Answer 4

You could use squoosh-cli. It's a project by Google Chrome Labs.

It supports many different formats and options. It does clever compression to reduce the size without resizing or loosing too much visual fidelity.

Usage (taken from their GitHub):

Usage: squoosh-cli [options] <files...>

Options:
  -V, --version                                          output the version number
  -d, --output-dir <dir>                                 Output directory (default: ".")
  -s, --suffix <suffix>                                  Append suffix to output files (default: "")
  --max-optimizer-rounds <rounds>                        Maximum number of compressions to use for auto optimizations (default: "6")
  --optimizer-butteraugli-target <butteraugli distance>  Target Butteraugli distance for auto optimizer (default: "1.4")
  --resize [config]                                      Resize the image before compressing
  --quant [config]                                       Reduce the number of colors used (aka. paletting)
  --rotate [config]                                      Rotate image
  --mozjpeg [config]                                     Use MozJPEG to generate a .jpg file with the given configuration
  --webp [config]                                        Use WebP to generate a .webp file with the given configuration
  --avif [config]                                        Use AVIF to generate a .avif file with the given configuration
  --jxl [config]                                         Use JPEG-XL to generate a .jxl file with the given configuration
  --wp2 [config]                                         Use WebP2 to generate a .wp2 file with the given configuration
  --oxipng [config]                                      Use OxiPNG to generate a .png file with the given configuration
  -h, --help                                             display help for command

There is also a very neat website to go with it: https://squoosh.app/. The website has a really cool before/after preview. I would recommend using the website on a single image to find good settings, then use the CLI to compress in bulk.

Answer 5

just for .png compress
// test with software screenshot img

X. test results first

 146K  redis_insight.png    //orig screenshot
 102K  redis_insight-1.png  //optipng compress
  38K  redis_insight-2.png  //pngquant compress

 135K  resp_app_tree.png
  96K  resp_app_tree-1.png
  47K  resp_app_tree-2.png

  88K  redis-commander_tree2.png
  63K  redis-commander_tree2-1.png
  27K  redis-commander_tree2-2.png

  61K  redsmin_tree.png
  44K  redsmin_tree-1.png
  22K  redsmin_tree-2.png

Carefully compare the result images, naked eye is almost indistinguishable.

1. optipng //lossless compression

$ optipng redis_insight.png -out redis_insight-1.png

//more compress level

$ optipng -o5 -strip all redis_insight.png -out redis_insight-1.png

2. pngquant //lossy compression

$ pngquant --speed 1 redis_insight.png -o redis_insight-2.png

--

ref: https://www.systutorials.com/compressing-png-images-on-linux/

Answer 6

The other solutions did not work for me. So I found a new approach:

At first, convert .png or any other format to .jpg using this command(you must have ImageMagick on your OS):

convert file_name.png file_name.jpg

Then use Jpegoptim to fit the size you need:

jpegoptim -v --size=240k file_name.jpg

Answer 7

If you are referring to jpeg images, de facto compression is not possible. Because jpeg is by definition a compressed file format (all noise and useless pixels are already removed). You can zip them alright, but the total size will remain about the same. The only advanced compression algorithm i know for jpegs is zipx. But zipx is proprietary by Winzip and ensures a max. size cut by 30% (in zipx archive mode).

To display your images on the web, first you should resize them (under 1MB per each one) and optionally convert them to png file format. PNG(=portable network graphics) is specially optimized for faster web transfer and faster display. Advanced users may even convert those images to webp format (Google's format for pictures, fastest loading algorithm).

You can batch convert pictures with XnConvert,then batch resize your pictures with XnView. Download the deb package from here: http://www.xnview.com/de/xnviewmp/#downloads , then right-click on it and open it with Gnome Software.

If you don't care about network loading speed, but care about quality, you should keep your images untouched and create a digital library for them. Maybe upload them onto a public server (Yahoo, Google, etc).

Answer 8

Better compressed result is with optipng ref

# install `$ sudo apt-get install -y optipng`
# see helpful syntax `$ tldr optipng`  # you may need install tldr `sudo apt-get install -y tldr`
optipng \       
    -o7         `# use best compression but quite slow ref. tldr optipng - fastest is w/ -o0` \
    -strip all  `# remove all metadata ref. tldr optipng` \
    *           `# all files or enter /path/to/your.png`