apply shader on PImage directly

Is something like this possible?

testImg = loadImage("someImage.jpg");
testImg.filter(shader);

The reason I ask is cause getting the color of an image directly is insane fast

int c = img.get(mouseX, mouseY);

Like 500 frames a second. But if I draw to the main canvas first (g) then it's really slow. Like:

int c =get(mouseX, mouseY);