I have GeoTIFF image. I want to know how to calculate specific area mean pixels values? Is field calculator for(value*count fields) right or get raster properties? Or what can I do?
If you are using ArcGIS the tool you are looking for is Zonal Statistics. You can mark out your your areas of interest with a shape file or feature class, and then use this as input along with your geotiff. I think QGIS has a similar zonal statistics tool if that's the software you are using.