This is the method my Drawing professor taught us to transfer the impressionist paintings we’re copying to our large pastel drawing paper. If you look closely at this photo, you’ll see that both my drawing paper and my reference image are covered in a grid of triangles.
It’s really easy, requires no math, and is way more accurate than the standard square grid! Just be sure to use a thin sharp pencil to do it.
Step 1: Draw Diagonal lines corner to corner on the image you want to enlarge.
Step 2: Measure from the edge of the frame to the intersection of the diagonal and draw a line straight across. Do the same vertically.
Step 3: Draw the other diagonals of your four new rectangles.
Step 4: Repeat as many times as necessary. My professor recommends at least 4 rectangles to a side for a landscape, and twice that for a figure.
Step 4: Stick your small gridded paper in the corner of the larger paper you’re drawing on, and extend the diagonal as far as you want to extend it. Draw super lightly!
Step 5: DO THIS ONCE and then remove the small picture and extend the diagonal. Drop a perpendicular line down from the diagonal to ensure the proportions of the larger image match your smaller image.
Step 6: Repeat the grid thing you did on the smaller paper.