This post lists the freeform feedback that Google Web DevRel received in its Summer 2019 image optimization techniques survey. Responses were solicited through Web Fundamentals and @ChromiumDev. The motivation for the survey was to find out why most sites don’t follow image optimization best practices even though they seem like a relatively easy way to improve performance. The response data isn’t listed here because there were flaws in the survey methodology.
srcsetattribute provides alternative image sources. You specify width or pixel density so the browser can choose the smallest image without needing to download images to calculate dimensions.
Why’s this important? Image services make it easier to optimize your images. You usually just upload one high-resolution version of each image and then use a web service API to optimize or transform the image as needed. Content Delivery Networks (CDNs) optimize the distribution and delivery of images and other website assets and sometimes provide optimization services, such as automatically delivering WebP images to supporting browsers instead of PNG or JPEG, without changing the file extension.