Despite writing the most comprehensive review of Codekit on the internet, there's a feature I've never spent much time with in Codekit: hooks. Most of my day-to-day dev is now in Gulp/Grunt/Webpack thus I haven't dedicated the time to set up a hook. Personal antidotes aside, here's a quick tutorial on how to get started with CodeKit Hooks, using a simple bash script to hook into the exceptionally powerful ImageMagick.

I highly recommend checking out my previous post on JPEG 2000 and WebP for a more indepth look at creating JPEG 2000 and WebP assets manually. The quick and short is there are (somewhat) better image formats that have been developed for lossy image compression, as the JPEG format is now 25+ years old. Modern web browsers support a smattering of new formats, but no single format is the clear winner. Safari supports JPEG2000 and HEIF. Chrome/Opera supports WebP. IE11/Edge supports JPEGXR. WebP/JPEG2000/JPEG-XR all support alpha layers, and presumably HEIF. JPEG2000 / WebP supports both lossy lossless image compression and JPEG-XR and JPEG2000 8-10 bit color. Firefox in atypical new format crisis the laggard (Remember Ogg anyone?). Sadly, JPEG-XR is a headache due to proprietary hell and is largely absent on macOS(OS X) or Linux, and HEIF is too avant-garde. BPG is pretty much DOA.

Creating a Hook

CodeKit 3 hooks allow CodeKit to tap into your Mac's terminal or Applescript, and trigger scripts to process files. This can be exceptionally handy. CodeKit's documentation is pretty solid for getting started with hooks but novice and junior devs might be a bit perplexed as to how or why you may want to do this.

For those who haven't used or perhaps heard of ImageMagick, it is a CLI utility that allows you to process images in any number of ways, like batch convert file formats, scale images, add borders, remove alpha masks and more. This tutorial only includes a very simple example of ImageMagick and will require some basic terminal usage. If you'd like to learn more basics of ImageMagick, I suggest reading Process images for your blog with imagemagick. Most novice developers should feel comfortable with the terminal enough to understand the few basic lines of code in this project. Junior developers should always be wary of executing random terminal commands, especially ones that ask you use sudo commands. All the bash scripts presented should be harmless and do not require sudo.

Step 1 - Homebrew

Install HomeBrew. In your terminal, type:

      brew - v

If this returns command not found, go to Homebrew's website and run the top command on the site to install HomeBrew.

Step 2 - Installing ImageMagick

Once homebrew has been installed or verified that it has been previously installed, its time to install imagemagick with JPEG2000 support as by default it does not come pre-baked with JPEG2000 support or webp. Fortunately Webp only requires installing seperately.

      brew install imagemagick --with-openjpeg
      brew install webp

Note: If you have a previous version of ImageMagick installed, you may need to run brew uninstall imagemagick to include JPEG2000 support. Annoyingly, ImageMagick will simply write JP2 files as the source file's file format if OpenJPEG is not present but with the caveat of appending the file with the new file suffix. This is very confusing, misleading, and frustrating. It took me around an hour to deduce that JPEG2000 requires OpenJPEG with ImageMagick. If you find ImageMagick creating JPEG2000 files that are massively larger than a PNG, Run magick identify -verbose filename to see if your JPEG2000 is actually a JPEG2000. If it reports your .jp2 file as a PNG, then you are missing OpenJPEG.

Step 3: Creating a CodeKit 3 Hook

In codekit, click on the gear icon, and click hooks. Click add new hook. For this example we're going to create a Shell script (Terminal bash script). Codekit has its own variables that can be passed into your shell script.

The basics of converting files in ImageMagick is pretty simple:

       convert input.file -quality (numeric setting) output.file

ImageMagick will export the file type based on you the suffix you choose. My goal is to create both a JPEG2000 and WebP image using imagemagick in the same directory as the original PNG.




    convert $CK_INPUT_PATH -quality 75 $webpFile
    convert $CK_INPUT_PATH -quality 50 $jp2File

Codekit settings

Notably there are many ways to go about this but I went for simple. Here's a quick run down of what the following code does:

  • $CK_INPUT_PATH and $CK_OUTPUT_PATH are both CodeKit 3 variables that are passed into a shell script. You can read about them here.
  • webpExt=".webp" and jp2Ext=".jp2" are bash vars I use to append a file name.
  • ${CK_OUTPUT_PATH%.png} removes .png from the output path.
  • webpFile="${CK_OUTPUT_PATH%.png}"$webpExt makes a variable with the correct path/filename - .png suffix + .webp suffix.
  • JPEG2000 support
  • convert $CK_INPUT_PATH -quality 75 $webpFile runs imagemagick's convert function on the CodeKit input file and then processes it with quality 75, and exports it the CodeKit 3 location with the proper file type that I set up in previous steps.
  • I repeat this on JPEG2000.

Pretty simple right?

Hopefully it was. If it wasn't, don't sweat it. The terminal is pretty much using a computer without handrails. CodeKit may buffer you from the terminal but it's completely worth your time as a developer to get comfortable with it and expected in most types of development.

The quality settings will need to be tweaked and often its better to do this sort of processing hand as I've had some wildly varying results on JPEG2000 and WebP, but this is a simple way batch convert PNGs to WebP and JPEG2000 images so Chrome/Safari users (99% of North American mobile users) can enjoy smaller image file sizes. Also, PNG with CodeKit's ImageOptim on PNGs can be hyper effective, and for simple images often best JPEG2000 and Webp.

Bonus: MozJPEG

If you'd like to use PNGs as sources, you can also create JPGs of your images using MozJPEG. MozJPEG only supports a few input formats. This script assumes you have a high quality PNG. Its recommended not to use Codekit's PNGquant on the source PNG. Notably this script could be exampled using ImageMagick accept @2x only images and resize them. Here's a more involved script that will take Retina PNGs and convert them into 2x and 1x JPEG2000, JPEG, and webp. The quality setting are arbitrary. You'll want to set up a source folder and build folder otherwise you'll end up with recursive files.

Install MozJPEG

    brew install mozjpeg

Bash Script for CodeKit (read above for notes)

    # vars for use later

    # make half size PNG path name, create a 1x PNG.
    convert  $CK_INPUT_PATH -resize 50%  $halfsizepngFile

    # webp
    convert $CK_INPUT_PATH   -quality 75 "${CK_OUTPUT_PATH%.png}"$twoX$webpExt
    convert $halfsizepngFile -quality 75 "${CK_OUTPUT_PATH%.png}"$oneX$webpExt

    # jpeg2000
    convert $CK_INPUT_PATH    -quality 70 "${CK_OUTPUT_PATH%.png}"$twoX$jp2Ext
    convert $halfsizepngFile  -quality 70 "${CK_OUTPUT_PATH%.png}"$oneX$jp2Ext

    # ppm temp for MozJPEG
    convert $CK_INPUT_PATH  $ppm2x
    convert $halfsizepngFile  $ppm1x

    # jpeg (MozJPEG)
    cjpeg -quality 70 $ppm2x > ${ppm2x%.ppm}$twoX$jpgExt
    cjpeg -quality 70 $ppm1x > ${ppm1x%.ppm}$oneX$jpgExt

    # remove temp ppm
    rm  $ppm2x
    rm  $ppm1x

Double bonus

I ported the same script as above to a jenky UI meant to be used outside of CodeKit.

Update August 19, 2017 - Added second script with image resizing + MozJPEG and corrected missing Webp installation step.