ValueError: Input 0 of layer sequential_1 is incompatible with the layer: : expected min_ndim=4, found ndim=3. Full shape received: [None, 256, 256]

Question

Everything is okay until I convert my image to grayscale. So the rgb\'s shape is (256, 256, 3) but grayscale has (256, 256). When I feed it, I get that error.