When setting image quality in my Canon EOS 1200d dSLR there are two options for the L, M and S1 size. What is the difference betwen these settings (I couldn't find it in camera documentation) ?
The size settings actually set two different things for any JPEG images taken by the camera: the resolution of the image being taken (the # x # size), and the quality setting for the JPEG compression for the image.
The L, M, and S sizes vary individually by the camera, but the numbers at the top in the blue bar tell you the pixel dimensions. So, in this case, your L size images are 5760x3840 (or 22MP). The larger the size you choose, the bigger the file will be, but the higher the resolution and the larger you can print out the image.
The "smoothness" of the quarter-circle indicates the quality level you're selecting. The higher the quality setting, the larger the file will be, but the more data is retained. JPEG is a "lossy" compression scheme that discards some of the color information in favor of making a smaller file. So, the smooth quarter-circle indicates "high" quality (large file, but less data discarded), and the stair-step quarter-circle indicates "medium" quality (smaller file, but more data discarded).