Hello Professor, that is good and very useful for us. let me sorry i am a GIS beginner. I would like to ask you how can i download world image or raster or some image area that i need. Thanks advance
Clip results in a raster that is just as large as the original, but with "NODATA" or null pixels everywhere outside of your clip polygon. If you really want to extract the raster down to the minimum size possible given your polygon extent, use "Extract By Mask" or define your polygon as an Analysis Mask and just export. Also watch out if you're using the default Nearest Neighbor resampling under Environment Settings>Raster Storage, as that is not appropriate for continuous data (use Bilinear or Cubic Convolution instead).
You may want to search for a tool called "Extract by Polygon", if you have the spatial analyst extension. You could also try "Exporting a Raster". and one other method is "Extract by Mask" again requiring Spatial Analyst.