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I'm using Sketch 51 on a macOS High Sierra. The Instagram icon looks great in Sketch but when I export as PNG it loses a lot of quality.
To the right we can see the icon in Sketch with zoom in good quality, and to the left we can see the image once exported.
I export the image with these options: - First I create an Artboard and adjust it to the image - Icon size is 45x45 - I export the artboard and choose PNG