Converting RGB to Grayscale Using ImageJ

A screencast tutorial demonstrating four methods to convert an RGB image into 8-bit grayscale

[MohdEnha]

So, according to your many ways.. which one is good for measuring the grey value intensity? Tq

[marcoa.ac.]

If it doesnt work because each plane is being converted separately, try:
test/playground/My image.tif");
selectWindow("My image.tif");
run("Make Composite");
run("RGB Color");
run("8-bit");