This is the single biggest time-saving thing I've learnt in years.
If you run your own business these days, especially any kind of creative business, chances are you'll have to do this at some point.
What is it?
To make low-res versions for online.
Or to make a specific size for a specific printed thing.
There are a million ways to do it.
If you use a Mac, there's one way that saves SO much time, it's unreal.
Using no new software.
Literally resize 100s of photos in seconds.
Jpegs, Tifs, PNGs, any normal image type.
Here's a demonstration video. The 5 steps explaining it are below.
So, Three Things.
1 - The Golden Rule.
ALWAYS MAKE SURE YOU'VE DUPLICATED THE FILES FIRST.
This tool overwrites the files you tell it to resize. So you do. not. want. to. mess. up. your. original. master. images.
Instead of changing the size and then saving as a new file, you need to make the new file first, and resize that one.
2 - Don't Get Freaked Out By The Terminal Thing.
This involves the tiniest, tiniest bit of code.
An eenie, weenie bit of code.
You won't break your computer, or The Matrix, or allow someone in Russia called Gustav to get into your bank account.
This little command called sips basically reprocesses images, in various ways.
The -Z bit, tells it to keep the aspect ratio the same. In other words, the height to width ratio.
The number you put in, that's where you say how big you want it to be.
If you feel more comfortable, you can copy and paste the command in, eg copy this (and change the size):
sips -Z 1000
Step by step instructions below
3 - Only Use This To Make Pictures Smaller.
Now, you could make them larger, it works, but I don't recommend using this method if you want high quality.
Making pictures bigger involves essentially guessing or making up information that doesn't exist.
And there are probably better tools for doing that if you need to.
1 - Identify all the files you want to resize.
Copy them into one single folder. For example, 'low_res' or 'sips_500' so it's clear they're smaller files.
2 - Open Terminal on your Mac. It's in Applications > Utilities, but the easiest way to open it is search.
The shortcut is cmd + spacebar.
Start typing Terminal and it should appear. Hit enter and it opens.
3 - Now type the sips command, with the -Z bit
(i.e. hyphen, capital Z. Everything in Terminal is case sensitive, so if it doesn't work, check you've not typed SIPS or Sips or -z by mistake)
And tell it what size you want the longest dimension to be, in pixels.
Doesn't matter if it's height or width. You don't have to specify. It'll keep the images looking exactly as they do now, just smaller.
So say the image is 1200x800 pixels (which is 3:2 ratio) and you specify 400, it'll resize to 400x266.
Because you've told it to make the longest side 400 pixels, and you've told it to keep the same aspect ratio (with -Z).
And because I picked an ugly number to use as an example that doesn't divide nicely.
Remember to leave an extra, single, space after the number.
If you want, copy and paste the code below, then change the size value:
sips -Z 1000
4 - Highlight all the image files and drag them into the terminal window.
It should list them. Again, make sure there's a single gap between the size value and the first file.
5 - Click on the Terminal window to make sure it's active, and press Enter.
It should go through them one by one and overwrite the files.
Any questions or things I may have missed, leave a comment below and I'll update anything that's not clear.