Create a halo around text in Python using PIL?

Question

I'm watermarking some pictures using PIL and I'm having a hard time reading some of the text (black text on dark background). I can't just change text color since I've got a wide array of background colors. Is there any way to add a halo effect around the text?

For example: https://i.stack.imgur.com/zhRe1.jpg The bottom text is what I've got, and the top text is what I'm hoping to get (colors aside). I really just need a thin outline around the text. Any ideas? I can upload some code if you really think it'll make a difference, but it's just a normal PIL ImageDraw.Draw command. Thanks!

Print the text three times. The first two with the outline color and offsets of (-1, -1) and (1, 1) and the third with the original color at the original position. — Matthias, Aug 17 '12 at 15:21
http://mail.python.org/pipermail/image-sig/2009-May/005681.html http://stackoverflow.com/a/8050556/442650 — Jonathan Vanasco, Aug 17 '12 at 15:54
PIL.ImageDraw has an `outline` option but it isn't valid for text. — Mark Ransom, Aug 17 '12 at 16:33
@HassanBaig sometimes it's worth knowing what *not* to try so you don't waste time on it. — Mark Ransom, May 05 '17 at 13:57
@MarkRansom: true that; that's why the unhelpful factoid is *helpful*. — Hassan Baig, May 05 '17 at 14:04
Does this answer your question? [Is there a way to outline text with a dark line in PIL?](https://stackoverflow.com/questions/41556771/is-there-a-way-to-outline-text-with-a-dark-line-in-pil) — Flair, Mar 15 '20 at 17:18

Jan Spurny · Answer 1 · 2012-08-20T09:39:52.697

If you don't care about speed too much, you can do it using composition:

draw text with halo color on a blank RGBA image
blur it
draw it again with text color
invert this image to get composition mask
"merge" with original image

For example:

import sys
import Image, ImageChops, ImageDraw, ImageFont, ImageFilter

def draw_text_with_halo(img, position, text, font, col, halo_col):
    halo = Image.new('RGBA', img.size, (0, 0, 0, 0))
    ImageDraw.Draw(halo).text(position, text, font = font, fill = halo_col)
    blurred_halo = halo.filter(ImageFilter.BLUR)
    ImageDraw.Draw(blurred_halo).text(position, text, font = font, fill = col)
    return Image.composite(img, blurred_halo, ImageChops.invert(blurred_halo))

if __name__ == '__main__':
    i = Image.open(sys.argv[1])
    font = ImageFont.load_default()
    txt = 'Example 1234'
    text_col = (0, 255, 0) # bright green
    halo_col = (0, 0, 0)   # black
    i2 = draw_text_with_halo(i, (20, 20), txt, font, text_col, halo_col)
    i2.save('halo.png')

It has many advantages:

the result is smooth and looks nice
you can choose different filter instead of BLUR to get different "halo"
it works even with very large fonts and still looks great

To get thicker halo, you may use filter like this:

kernel = [
    0, 1, 2, 1, 0,
    1, 2, 4, 2, 1,
    2, 4, 8, 4, 1,
    1, 2, 4, 2, 1,
    0, 1, 2, 1, 0]
kernelsum = sum(kernel)
myfilter = ImageFilter.Kernel((5, 5), kernel, scale = 0.1 * sum(kernel))
blurred_halo = halo.filter(myfilter)

The part scale = 0.1 * sum(kernel) makes the halo thicker (small values) or dimmer (big values).

I think a proper outline would look better in this case, as in the example in the question, but this is the correct way to generate a "halo". The only downside is that the wider you make the halo the dimmer it gets. I'm a bit disappointed that PIL doesn't give a more straight-forward way of blending an RGBA image over another. — Mark Ransom, Aug 17 '12 at 18:31
Cool thanks. Just one question... the blur is very blurred out... with black text and white blur... the blur does in fact turn out invisible on a black background. How can we sharpen this? Maybe that is what you mean by thicker halo? — Jonny, Jul 07 '15 at 03:48
@Jonny yes, that would probably be it. Or, you can use different filter (see: http://pillow.readthedocs.org/en/latest/reference/ImageFilter.html), play with *scale* or *offset* values in http://pillow.readthedocs.org/en/latest/reference/ImageFilter.html#PIL.ImageFilter.Kernel — Jan Spurny, Jul 07 '15 at 12:36

Create a halo around text in Python using PIL?

1 Answers1