crw CRW stands for the RAW image format.This format is gaining a lot of popularity nowadays since a lot of the cameras people utilise ( the single lens reflex cameras ) are using this format. The data coming from the image sensor, in the case of the RAW format, is by far the most basic and unprocessed of all. CRW is also known as digital negatives, the RAW image files have quiet the same use as the negatives used in film photography.
png PNG stands for portable network graphics. It is the raster graphics format associated with the .png filename extension. Unlike GIF format, the limitation of 256 colors does not hold with the PNG format. In fact this among other reasons was the motivation behind development of the PNG format to improve upon the GIF format. The PNG format however uses a single image format and thus does not support animations. Because the format was engineered to ease the distribution of graphic files across computer networks it is also not well suited for professional graphics.