I recovered 30 gigs of storage on my MBP (MacBook Pro) with this simple hack of converting my PNGs to JPEGs. Here’s how.
If you own a Mac or an iPhone, you’ll notice both devices save “screenshots” with a PNG extension. Portable Network Graphics (.png), an image file format is uses lossless compression to save your images. You maybe thinking this lossless compression is the best format but the reality is JPEG, a lossy compression, is just as good at retaining image quality at a MASSIVE fraction of the size of a PNG.
Image sizes really matter when your device runs 1080p+ resolutions (most modern Macs) or new OLED iPhones. A full size (no crop) screenshot on my MBP with a resolution of 2080×1080 yields a 7MB (7168kb) image. A JPEG equivalent is 500kb. That’s ~14x smaller. If you are like me and take screenshots as reminders or todos (GTD baby!) then you’ll be chewing through storage fast.
100 of these PNGs and you’ll be reaching the 1Gb territory.
With storage being dirt cheap who cares right? Not so. Laptops with external drives are annoying and iPhones do not have extension cards. Furthermore, data transfer is a burden consider upload speeds are always conveniently ignored yet important if you are backing up to the cloud. And let’s face it, who’s got time to sit around waiting when the same lot of photos with identical quality (assuming you aren’t blowing them up on a wall) can be backed up to your Dropbox cloud storage 14x faster. GTD baby!
Did I mention this will also speed up your Spotlight searching, indexing, extend your SSD life and open those images faster.
Convert PNGs to JPEGS
PNG are uncompressed images from things mainly like Screenshots on your Mac or iPhone. They don’t need to be PNG unless you really are picky about the quality of text sharpness. ie. Under JPEG text becomes a tad more blurry since compression reuses surrounding pixels to make image smaller.
Overall, the chance of you retaining PNGs is low unless you do a lot of photo editing and need that pixel level detail especially for font/text clarity.
 Identify Opportunities
Run a scan to identify where the opportunities (PNGs) are located on your drive.
$ find . -type f -iname '*.png' | wc -l
find . -type f finds all files ( -type f ) in this ( . ) directory and in all sub directories, the filenames are then printed to standard out one per line.
This is then piped | into wc (word count) the -l option tells wc to only count lines of its input.
If you only want files directly under this directory and not to search recursively through subdirectories, you could add the -maxdepth flag:
$ find some_directory -maxdepth 1 -type f | wc -l
The key to that case-insensitive search is the use of the -iname option, which is only one character different from the -name option. The -iname option is what makes the search case-insensitive.
Create JEPG versions of the PNGS and remove old PNGs. There is no need to keep the old PNGs. They are the ones that take up all the space.
Run this on a small subset of your PNGs to make sure you are happy with the resulting JPEG.
$ mogrify -format jpg *.png && rm *.png $ mogrify -format jpg *.PNG && rm *.PNG
or convert and keep the original PNG
$ mogrify -format jpg *.png
How much space did you recover?