The platform tries to make sure images are as high-quality as possible without causing download sizes to be too large for recipients. If download sizes are large, this could affect a recipient's mobile data usage and the image's download speed.
If you're unsure what image sizes to use or don't want to resize your images, we recommend uploading images in JPG format. We'll then do the rest.
However, if you want more control over your images, here's a quick guide to what we do with different formats.
Maximum file size
The maximum filesize for individual images is 10 MB; images that exceed this size will fail to upload.
PNG and GIF images
We don't adjust PNG or GIF images. If an image is uploaded at 1000 px wide, it's sent at that exact resolution.
If you want to scale your PNG or GIF images, you can use the picture editor available from within the image manager.
We re-scale JPGs, depending on where and how you use them. For example, if you place a high-resolution JPG image around 1000px wide into a campaign at 300px wide on-screen, to keep the file size down, we'll re-scale the original image to 300px wide to match this.
However, in our mobile responsive campaigns, we have a minimum JPG image width of 660px. This ensures the image remains crisp on high-DPI devices, such as phones and retina screens.
JPG quality loss
JPG is a lossy format, meaning it is compressed to reduce the quality of the source image. When we re-scale, we use a quality value of 90%, meaning there will be a slight drop in quality. This won't be noticeable in most cases, but occasionally you may notice that the final result isn't as good as the original. In these cases, we'd recommend using a PNG or GIF instead.
Optimising for retina displays
Generally, whatever format you use, you should ensure your images are at least 600px wide when you upload them to the platform.
JPG images tend to be smaller in file size than their PNG counterparts - especially for photography.
Therefore, for the most part, we'd recommend using JPG files. However, PNG or GIFs are better for logos or icons in terms of quality and sometimes file size.
If you're trying to get a full-width image to work well on a high-DPI desktop display, such as a Mac with a retina screen, then upload your images as PNG files at around 1200px or twice the width of your campaign. JPG files, in this instance, will be downscaled to the width of the campaign.
If image sharpness is important to you, then we recommend using PNG or PNG-24 for your images. These will ensure that your images remain as sharp as the originals on all devices. But do be aware of file sizes.
Many people have limited bandwidth on mobile contracts, so forcing them to download a large number of high-resolution images will impact that.