Optimal image size for icon in Watch app table row

What is the optimal/max image size for an icon in a Watch app table row, in order to avoid scaling of the original image?

While the default row is 40 points high, an image could generally be as large as 36 points (for 42mm or 34 points for 38mm), assuming default interface group and image settings, to avoid scaling the image.

Answer to original question:

There's no optimal point size for a WKInterfaceTable row image.

It's more of a UX issue, since the size of an image is based on how prominent you want it to be versus any adjacent text. If you compare these two examples, the Apple Music watch app uses a 24 point image, while the WatchKit Catalog sample code uses a 35 point location marker image.

It's easier to focus on the Music text, since the font size is larger, and the image is not significantly larger than the text. It's more difficult to concentrate on the WKCatalog text, because of the tendency for our eyes to be drawn to the much larger location marker.

Regardless of the size you choose, ensure that your pixel (not point) sizes are even for both width and height, to avoid any image blurring.