As it is inherent in the double-triangle plot, you have precisely quantify the various feldspars, foids and quartz for a correct classication of your plutonic rocks

Dear Anamika Gogoi

You can use an image analysis software, like ImageJ, on a whole thin section scan/photo stitching. You need to carefully separate each phase based on its color. This is simple with femic/sialic minerals (adjusting contrast/brightness may saturate all sialic to white and all femic to black), but can be tricky with minerals of similar color (e.g. feldspars). In the latter case, you may need to manually contour grain by grain, before estimating area% with an image analysis software.

There are also techniques that can map an area of a thin section to estimate composition and area% of phases (EBSD, X-Ray maps, EDS-SEM), but I don't think they can be performed with high accuracy on entire thin sections.

I strongly recommend ImageJ. There are also many tutorials on youtube.

https://imagej.nih.gov/ij/download.html

If you need a quick estimate and don't require high accuracy, another option is to use visual estimation diagrams like the one attached. This is an example for sedimentary rocks. I am sure that you may find something better for plutonic rocks.

Best,

Samuele