How to calculate raster statistics for each values in a band?

Question

I have one raster scene that contains one band with multiple pixel values (0-14). Each values represent deforestation in certain year (0=no tree cover loss, 1=loss in 2001, 2=loss in 2002, and so on) and I need to calculate the deforestation statistics for each years (e.g. statistics for each pixel values in that scene).

I've tried using Zonal Statistics, but it only gives me a lump of all values (total count in zonal statistic = sum of all values). What I need is to count how many pixels have value '1', '2', and so on. Any suggestion on what tool(s) to use?

Answer 1

You can use Zonal Raster Statistics (also called Zonal Grid) tool to count the number of pixel in each class. The tool will create a new CSV file with the number of pixels for each category.

The only required parameter is the classified image (Zonal Grid) that contains the categories you want to calculate.

In the following example, I have a land use raster with 8 classes. When I run Zonal Raster Statistics tool, I got the following result:

Here is the output:

The tool can be found from Processing toolbox -> SAGA -> Geostatistics -> Zonal Raster Statistics

Answer 2

You might want to take a look at the SAGA Zonal Grid statistics. This is available in Processing if you have SAGA GIS installed. I've not tried this yet but it looks like it will do what you want.

According to the documentation this can create a contingency table (cross-tabulation) which includes the number of pixels ("n") in each category for each polygon.

The normal zonal statistics takes a polygon and raster layer as input.

However, this algorithm takes two (or more) raster layers instead. So you will need to convert your polygon layer to a raster layer (using Raster > Conversion > Rasterize) to use as your zonal grid, and your categorised raster as the categorical grid.

The output should be a table.