Image optimisation refers to minimising the size of an image file so that it can be quickly downloaded no matter whether you are on a high speed broadband connection or connected via your mobile to a slow network.
One of the most common mistakes that website owners make is to rush adding an image to their website. They may have had some photos professionally taken, get the originals straight from the photographer and upload it to their website – and quite often these are several MB in size and a very high resolution (great for printing on large print media).
What they should have done is optimise their images first.
This means doing the following:-
- Resizing the image from however many thousands of pixels in width and height to the maximum needed for their website;
- Saving it as a compressed image (often either a jpg or a png file) – you can get away with up to 40% of the quality of a print ready image, and the human eye can barely notice the difference.
- Of course you’d also want to rename the image and make sure you add an ALT TAG to it when it is uploaded to the website (but that’s a slightly different subject).
Taking the image used in this post as an example. I downloaded it from pixabay.com and as an original image it was 5400 pixels wide by 3644 pixels tall. I cropped it down to 800px by 500px, and then saved it as a jpg file at 40% of it’s original quality. It was 3.11MB in size, it is now just over 35KB. A massive saving, and far easier for a user on a mobile device to download (especially if there are alot of them).