Drawing a smooth line with a Python image library

Question

I draw a bunch of lines using the Python ImageDraw.line () image library, but they look awful since I can't find a way to smooth them. How can I use aliased strings in PIL? If PIL cannot do this, is there another Python image management library that can?

Answer 1

aggdraw provides a nicer drawing than PIL.

Answer 2

This is a really quick hack function to draw a smooth line with PIL, which I wrote after searching for the same problem, having seen this post and could not install aggdraw and be in a short time. This is the implementation of the Xiaolin Wu line algorithm. Hope this helps someone work for the same thing!

:)

"""Library to draw an antialiased line.""" # http://stackoverflow.com/questions/3122049/drawing-an-anti-aliased-line-with-thepython-imaging-library # https://en.wikipedia.org/wiki/Xiaolin_Wu%27s_line_algorithm import math def plot(draw, img, x, y, c, col, steep, dash_interval): """Draws an antiliased pixel on a line.""" if steep: x, y = y, x if x < img.size[0] and y < img.size[1] and x >= 0 and y >= 0: c = c * (float(col[3]) / 255.0) p = img.getpixel((x, y)) x = int(x) y = int(y) if dash_interval: d = dash_interval - 1 if (x / dash_interval) % d == 0 and (y / dash_interval) % d == 0: return draw.point((x, y), fill=( int((p[0] * (1 - c)) + col[0] * c), int((p[1] * (1 - c)) + col[1] * c), int((p[2] * (1 - c)) + col[2] * c), 255)) def iround(x): """Rounds x to the nearest integer.""" return ipart(x + 0.5) def ipart(x): """Floors x.""" return math.floor(x) def fpart(x): """Returns the fractional part of x.""" return x - math.floor(x) def rfpart(x): """Returns the 1 minus the fractional part of x.""" return 1 - fpart(x) def draw_line_antialiased(draw, img, x1, y1, x2, y2, col, dash_interval=None): """Draw an antialised line in the PIL ImageDraw. Implements the Xialon Wu antialiasing algorithm. col - color """ dx = x2 - x1 if not dx: draw.line((x1, y1, x2, y2), fill=col, width=1) return dy = y2 - y1 steep = abs(dx) < abs(dy) if steep: x1, y1 = y1, x1 x2, y2 = y2, x2 dx, dy = dy, dx if x2 < x1: x1, x2 = x2, x1 y1, y2 = y2, y1 gradient = float(dy) / float(dx) # handle first endpoint xend = round(x1) yend = y1 + gradient * (xend - x1) xgap = rfpart(x1 + 0.5) xpxl1 = xend # this will be used in the main loop ypxl1 = ipart(yend) plot(draw, img, xpxl1, ypxl1, rfpart(yend) * xgap, col, steep, dash_interval) plot(draw, img, xpxl1, ypxl1 + 1, fpart(yend) * xgap, col, steep, dash_interval) intery = yend + gradient # first y-intersection for the main loop # handle second endpoint xend = round(x2) yend = y2 + gradient * (xend - x2) xgap = fpart(x2 + 0.5) xpxl2 = xend # this will be used in the main loop ypxl2 = ipart(yend) plot(draw, img, xpxl2, ypxl2, rfpart(yend) * xgap, col, steep, dash_interval) plot(draw, img, xpxl2, ypxl2 + 1, fpart(yend) * xgap, col, steep, dash_interval) # main loop for x in range(int(xpxl1 + 1), int(xpxl2)): plot(draw, img, x, ipart(intery), rfpart(intery), col, steep, dash_interval) plot(draw, img, x, ipart(intery) + 1, fpart(intery), col, steep, dash_interval) intery = intery + gradient 

Answer 3

I had a similar problem, my lines had rough edges where the directions changed. I figured out how lines are drawn in iOS and came up with this code. It overlays the rounded ends of the lines at the ends of the lines and really cleans things up. Not exactly anti-aliasing, but I'm completely new to PIL, and it was hard for me to find an answer that I thought I would share. Needs some tweaking, and probably a better way, but does what I need :)

 from PIL import Image import ImageDraw class Point: def __init__(self, x, y): self.x = x self.y = y class DrawLines: def draw(self, points, color, imageName): img = Image.new("RGBA", [1440,1080], (255,255,255,0)) draw = ImageDraw.Draw(img) linePoints = [] for point in points: draw.ellipse((point.x-7, point.y-7, point.x+7, point.y+7), fill=color) linePoints.append(point.x) linePoints.append(point.y) draw.line(linePoints, fill=color, width=14) img.save(imageName) p1 = Point(100,200) p2 = Point(190,250) points = [p1,p2] red = (255,0,0) drawLines = DrawLines() drawLines.draw(points, red, "C:\\test.png")