Accessing raster attribute table in QGIS?

This feature request might fill your needs: http://hub.qgis.org/issues/4321

There is still no such function in QGIS as raster attributive table (as it was in ArcMap). However, you can get similar output by running Raster layer unique values report. This function counts unique values (which is perfect for integer rasters) and even calculates the area.

The output will look smth like:

Extent: 103.2208100000000002,52.1505000000000010 : 141.5203300000000013,73.7999700000000018

Projection: WGS 84 (EPSG:4326)

Width in pixels: 33991 (units per pixel 0.00112675)

Height in pixels: 19214 (units per pixel 0.00112675)

Total pixel count: 653103074

NODATA pixel count: 339328216

Value   Pixel count Area (deg²)
0   1549588 1.96732049625739
1   248748550   315.8053113661866
2   17323972    21.99410759001047
3   24404810    30.98377305468765
4   3532094 4.48426350804714
5   7962170 10.10858385305366
6   10253674    13.01782346155333