How large is the image file resolution? Do you have enough memory? Which import method were you using? Color as texture (vector Drawing) or Keep as Original bitmap?
Or are you using old version of Harmony? Then which version? uncheck ‘vectorize imported items’ option is from older version of Harmony or other products.
if I uncheck ‘vectorize imported items’ but it lowers the resolution
importing image as bitmap creates a small thumbnails in Harmony to increase the performance for bitmap image. The final render uses the real image so there is no loosing quality of the bitmap. If you need to trace the bitmap to create a matte for example but having a difficulties due to small bitmap size, you can increase the quality of bitmap temporary by selecting Camera Menu>view>Bitmap File Quality.