I have Landsat 7 images from 2011 to 2016 for my agricultural studies. First I corrected the slc-off problem of band 3 and band 4. Then I calculated the NDVI using both the raster calculator and the vegetation index (slope based) processing toolbox. I realised that the data range of the NDVI Images are different. The raster calculator results between -0.242 - 0.568 and the vegetation index under processing toolbox results between -0.225993 - 0.553768. Can this be due to rounding or is there something that I may be missing?
I also use the raster layer statistics tool to see if these two NDVI images are really different. The results are:
From vegetation index algorithm: Valid cells: 42384039 No-data cells: 15942162 Minimum value: -0.991935491562 Maximum value: 0.982142865658 Sum: 2857838.41327 Mean value: 0.0674272315876 Standard deviation: 0.184433938177
From raster calculator (which I choose from the dropdown menu bar of Raster) Valid cells: 42696562 No-data cells: 15629639 Minimum value: -1.0 Maximum value: 1.0 Sum: 2862525.41327 Mean value: 0.067043463904 Standard deviation: 0.20274331204