generates a full LUT from part of an existing one. Offrande au grand manitou des LUTs!

new_LUT_from_selection.ijm

// Kevin Terretaz @kwolbachia 10.11.21
// open the LUT you want to transform as a 256x32 8bit image
// run the macro
run("Select All");
waitForUser("adjust the selection to crop");
setBatchMode(1);
run("Duplicate...","duplicate");
run("RGB Color");
run("Scale...",
	"x=- y=- width=256 height=65 interpolation=Bicubic average create");
R = newArray(1); G = newArray(1); B = newArray(1);
for (i = 0; i < 256; i++) {
	c = getPixel(i, 2);
	R[i] = (c>>16)&0xff; 	G[i] = (c>>8)&0xff;		B[i] = c&0xff;
}
newImage("new LUT", "8-bit ramp", 256, 32, 1);
setLut(R, G, B);
setBatchMode(0);