Images are notoriously slow to load in email messages and websites. Unfortunately images are very large in file-size meaning much more data needs to be downloaded for an image as opposed to text.
Three Ways to Improve Image Load Speed
Happily there are a few things we can do to make images load more quickly. Below are four simple ways of reducing image file sizes and therefore making them load more quickly in your email campaigns.
Use the best image file-type
The most widely supported image file-types in email are JPG/JPEG, PNG and GIF. Generally using the most appropriate file-type will result in a smaller file size and often a better quality image:
- JPG/JPEG: Used for photographs.
- PNG and GIF: Used for line drawings.
- GIF: Used for image animation.
Reduce Image Dimensions to Load Images More Quickly
The width of most email campaigns sent from Mailchimp is 600 pixels wide. To reduce image file-size therefore ensure that images you add to your campaigns are 600px wide. I often see people adding images that are, say, 900px wide but this in no way improves the visual quality of an image in a campaign.
In Mailchimp you can constrain image dimensions to (hopefully) show your images at a better quality on high resolution screens. Test this if you’d like to but be aware that the file-size of a 1200px wide image will be significantly larger than a 600px wide image.
Reduce the Image Pixels Per Inch
Pixels per inch (ppi) is a measure of quality when referring to printing an image. On your website or email messages, ppi (also called dpi) is irrelevant.
For your email campaigns save JPG and JPEG images as 72 ppi. The image will display on a screen at the same quality as if the ppi were much higher but the file-size will be much smaller.
It’s simple to change the ppi of an image in Photoshop and other image editors. There are also numerous online tools that will assist.
Compress Your Images
There are two categories of image compression; lossy compression (where the image quality may suffer) and lossless compression (image quality doesn’t reduce but file size does). All images should be compressed before being added to an email campaign.
There are many online and downloadable image compression utilities. Kraken and Compressor.io are good online image optimization tool.
Testing Image Optimization
To show how effective the four image optimization suggestions above are, I performed a quick test.
The image above is of Brisbane, Australia. The original copy was a PNG file at 1200 pixels wide. The image filesize was 1.5MB.
I then created a copy, changed to JPG, resized to 600px wide (making sure to stay at 72 ppi) and then performed lossless compression using FileOptimizer. The resulting image was 267kb.
By following the four image optimization steps the image size was reduced to approximately 20% of it’s original size without sacrificing quality. This means a faster loading email campaign for your contacts!
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