How to measure impact of substituting images for different views?

My question relates to the technique described in Campaign Monitor's guide on responsive email, particularly the section headed 'Using background images for better headers'.

Of course, doing this increases the number of http calls, which could potentially affect the load time of the email.

My question is, how do you weigh up the benefit of a substituted image against the potential affect on the user's load time?

In my particular case, I'm working on a design with an image that's 64.82K and which can scale fluidly across views using a media query, however the result is not a particularly good aesthetic for this particular email. My alternative is to have two images that substitute at different dimension ratios - one for a mobile view (48.2K) and one for a desktop view (13.43K). This gives me a much better aesthetic for about the same download size, but with an extra http request.

Do I need to worry about the effect this would have on the reader? How do I estimate what effect substituting images would have?

roshodgekiss roshodgekiss, 4 years ago

Hi Cheli, I guess the best advice here is simply to test out both scenarios on a mobile device, using a cellular data connection. If you find that load times are considerably more when substituting images, that could be an issue. Note that we serve images via a pretty fast and sturdy CDN, so I foresee that the extra HTTP request won't make much of a difference. Let us know how you go :)

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Cheli, 4 years ago

Thanks for the advice Ros :)

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