How to use PIL floodfill in python?

Question

I am trying to color a bar using python’s PIL package. This is the original bar:

I would like to color the entire inner part with just one color. I tried to use the floodfill for that reason:

from PIL import Image, ImageDraw

im = Image.open('progress.jpeg')
width, height = im.size
center = (int(0.5*width), int(0.33* height))
yellow = (255, 255, 0, 255)
ImageDraw.floodfill(im, xy=center, value=yellow)
im.save('result.png')

And I got the following result:

Initially, I imagined that the floodfill color all pixels that are between the specified width and height in the argument xy. As I took 1/3 of the height and half of the greeting, he painted yellow the inner area from left to right, from half. However, if I use 100% width, the program does not color anything. So obviously my interpretation is wrong.

How does floodfill work? How can I color the internal bar completely?

Answer 1

Remember the function of the "bucket" of Paint? The floodfill works similarly: you pass a color and an XY point, and the PIL tries to "fill" the region around the XY point with the desired color.

Of course the cut-off point to define the boundary region of the fill will depend on your application - maybe you want the fill to pick up color regions similar but not identical the color of the region in which you added the color. You can control this with the argument thresh.

To color the entire bar in your case, I believe the simplest is to use the floodfill twice - passing an XY position within the green region, and an XY position within the black region. If all pixels in each region have the same intensity, you don’t even have to worry about the argument thresh.

Edit

I tested your image and the color along the bar is really not homogeneous - but if we use a thresh high enough, we can fill the bar fully. Below the example of code that does what you want:

im = Image.open('progress.jpeg')
width, height = im.size
green_region = (int(0.4*width), int(0.33*height))
black_region = (int(0.6*width), int(0.33* height))
yellow = (255, 255, 0, 255)
for region in (green_region, black_region):
    ImageDraw.floodfill(im, xy=region, value=yellow, thresh=150)
im.save('result.png')

Output:

The documentation of floodfill is here.

Examples:

• Input image:

• Running your code in the image (uses the default argument thresh=0 - note the yellow pixel alone in the hat):

• Adding the argument thresh=30:

• Adding the argument thresh=100: