Is there a way to turn off blending for colour grading LUTs?

I’d like to be able to limit the screen’s colours to a specific palette. However if I use colour grading to achieve this it will also display blended versions of the chosen colours, even if filtering on the LUT texture is turned off. For example the LUT below contains only solid white and black, but the end result includes blended grays. What do?

134502-bilevel_1bit_palette_color_test_chart.png