I have scoured the web for plugins and articles to help me solve something that seems pretty basic, but couldn't find anything.
I want a way to create custom versions, particularly sizes, of an image on a per-image basis.
I know I can register a specific size of image and WP will create it for every image that is uploaded.
But what I want is to be able to create a scaled version of an existing image from the media library UI.
For example, let's say I upload image A. WP creates a version by default that is 600px wide and I use it at that size throughout the website.
But then I have a call-to-action box in an article where I want to display the image, but with a width of 175px.
So, I want to create a version of that image at the 175px width, as well as a retina 2x 350px wide.
When I add the image to the box, I want WP to output a srcset that includes those two additional sizes so that the browser can pick whichever image it thinks is best for the situation.
I don't want to specify those 175px and 350px as additional image sizes for ALL images, because I won't need it for most of them.
This seems like a pretty common use-case to me, but despite that I couldn't find anything.
Perhaps I am using the wrong keywords and I hope someone here can point me in the right direction.