In my workflow I use PhotoShop CC layers to export everything using Generate > Image Assets. I set all my text layers to .svg, photos to .png or .jpg, Works brilliantly as you can adjust things in photoshop, refresh your browser and the changes are applied with no exporting. Unfortunately with .svg there are no parameters that you can set in PS. For bitmaps you can add .png24 to the end or .jpg70%. I have to outline the text layer too so that the svg is font independent. The weight of the text changes with outlining, more noticeably on smaller size text which was a major pain point. Illustrator gives far better control but it is adding a second app to my work flow which I am not jazzed about.