Image scaling on high DPI screens

[Gary Wood]

Our company uses Google Apps mail, with some staff using Outlook IMAP as their mail client. I am having problems inserting images into signatures and having them display consistently on some of our laptops that have high dpi displays with desktop scaling enabled (>100%). The problems are as follows:

• Emails sent from Gmail's web interface don't display correctly in high dpi Outlook. The images don't scale, but the text does. The same emails look fine in Outlook if desktop scaling is set to 100%. (EDIT: It turns out that they only don't display correctly the first time the email loads! If you close the message and then reopen it, they are scaled correctly.)
  
• Emails sent from high dpi outlook look fine in Outlook itself, but when they are viewed in Gmail, the images are too big: they are scaled up by the display scaling set on the sending machine (e.g. 125%, 150% or 175%).

How can I achieve consistent behaviour, so that:

• Emails sent from Gmail's web interface correctly scale in high dpi Outlook?
• Emails sent from high dpi outlook do not scale up when viewed on non-scaled screens (either in Outlook or Gmail)?

 

[Gary Wood]

I've done some more investigating on this. The key issue I'm now facing is as follows. When I insert an image into my Outlook signature on a high-dpi screen with desktop scaling enabled, it looks fine, and appears the correct size relative to the text alongside it. If I sent a test message to myself and open it on the high-dpi screen in Outlook, it's fine there, too. However, if I open the same test email on a screen without desktop scaling enabled (i.e. at 100% scaling), then the image is too big, so that it looks out of proportion from the text alongside it, and severely pixellated.

I know what the cause of this is, but I don't know how to fix it! The cause is that Outlook on the high-dpi screen scales the image when it's inserted so that it is the right size relative to the text alongside it, i.e. it increases it by the scaling factor of the desktop. Thus, it looks fine on the high-dpi scaled screen. However, that scaling is not applied just to the view, the scaled pixel sizes get applied to the image in the sent message, too. Thus, an image that is 100x100px gets scaled up to 175x175px (on a 175% scaled screen). Then, when the email is viewed on a screen with a smaller scaling factor applied, it appears too big.

So, the big question is this: how can I stop Outlook from rewriting the pixel values of the images in my signature when it scales them for display purposes?