[.NET] Low resolution images in an image set don't stretch as they do on other platforms

Platform

What platform is your issue or question related to? (Delete other platforms).

• .NET WPF

Issue

The below card renders differently on .NET compared to UWP and Javascript.

Javascript behavior (UWP is similar):

.NET behavior

Json:

{
  "$schema": "http://adaptivecards.io/schemas/adaptive-card.json",
  "type": "AdaptiveCard",
  "version": "1.2",
  "body": [
    {
      "type": "ImageSet",
      "images": [
        {
          "type": "Image",
          "url": "http://messagecardplayground.azurewebsites.net/assets/person_w1.png"
        },
        {
          "type": "Image",
          "url": "http://messagecardplayground.azurewebsites.net/assets/person_m1.png"
        },
        {
          "type": "Image",
          "url": "http://messagecardplayground.azurewebsites.net/assets/person_w2.png"
        },
        {
          "type": "Image",
          "url": "http://messagecardplayground.azurewebsites.net/assets/person_m2.png"
        }
      ]
    }
  ]
}

[andrewleader]

A patch can be fine, but we should be clear on whether this was a regression or not. If it was a regression, we definitely need to patch it. If .NET always behaved like this, we could wait till 1.3.

JavaScript and UWP behavior is correct, setting the “size” property to one of the sizes (small/medium/large) should force the image to that size, even if it means upscaling the image.

[shalinijoshi19]

@almedina-ms assigning to you for post 1.2 investigation and fixing. We need to figure out if this is a regression or not. If it is, then it makes the case for a post 1.2 patch release else we can include it for 1.3 directly.