Develop Reference

Pillow - GIF File Size

The following program uses the Pillow package (3.4.2) to create a very simple GIF file. The file size is 11.2 KB.
from PIL import Image, ImageDraw
img = Image.new('P', (400, 300))
draw = ImageDraw.Draw(img)
draw.rectangle((0, 0, img.width, img.height), fill='black')
draw.line((10, 10, img.width-10, img.height-10), fill='cyan', width=5)
del draw
img.save('Test.gif')
If I open this file in Microsoft Paint and Save As with a different name, the file size becomes 1.90 KB.
Why such a big difference? Can I make Pillow use whatever format the Paint uses to get the same small size?

If your not making a animated GIF you can change img.save('Test.gif') to img.save('Test.png') the file size will then become 1.52KB.

You could use jpeg and optimise parameters as in here
img.save('Test.jpg',optimize=True,quality=95)

python3.5 PIL Image not displaying image

The following code does not display the image lists.jpg (in current dir):
print(dir(Image)) displays components; im.size, im.filename, im.format all return correct values.
What have I not done to display this jpg file?
from PIL import Image
im = Image.open("lists.jpg")
im.show() # did not work - perhaps due to the environment Jupyter Notebooks
Solution: replaced module with another with immediate results.
from IPython.display import Image
Image(filename='lists.jpg')

I know it is quite late to post but I will do it for new readers.
This problem arises in case of Jupyter Notebooks. Using show() does not display the image. So discard calling show() like in the code below. This will display the image in the output of the cell.
from PIL import Image
im = Image.open("lists.jpg")
im

To display the image on screen:
from PIL import Image
im = Image.open("lists.jpg")
im.show()
See also http://pillow.readthedocs.io/en/4.0.x/reference/Image.html

Image pasted with PIL produces artifacts

I have a bunch of images I need to put a text-overlay on top of. I created the overlay with GIMP (PNG with transparency) and tried pasting it on top of the other image:
from PIL import Image
background = Image.open("hahn_echo_1.png")
foreground = Image.open("overlay_step_3.png")
background.paste(foreground, (0, 0), foreground)
background.save("abc.png")
However, instead of displaying a nice black text on top, I get this:
overlay.png looks like this in Gimp:
So I would expect some nice and black text instead of this colorful mess.
Any ideas? Some PIL option I am missing?

As vrs pointed out above, using alpha_composite like this answer: How to merge a transparent png image with another image using PIL
does the trick. Make sure to have the images in the correct mode (RGBA).
Complete solution:
from PIL import Image
background = Image.open("hahn_echo_1.png").convert("RGBA")
foreground = Image.open("overlay_step_3.png").convert("RGBA")
print(background.mode)
print(foreground.mode)
Image.alpha_composite(background, foreground).save("abc.png")
Result:

python imaging library save function

I have just done some image processing using the python image library (PIL) and I can't get the save function to work. the whole code works fine but it just wont save the resulting image. The code is below:
im=Image.new("rgb",(200,10),"#ddd")
draw=Image.draw.draw(im)
draw.text((10,10),"run away",fill="red")
im.save("g.jpeg")
Saving gives an error as unknown extension and even removing the dot doesn't help.

Use .jpg:
im.save("g.jpg")
The image library determines what encoder to use by the extension, but in certain versions of PIL the JPEG encoder do not register the .jpeg extension, only .jpg.
Another possibility is that your PIL installation doesn't support JPEG at all; try saving the image as a PNG, for example.

Replace
draw=Image.draw.draw(im)
with
draw = ImageDraw.Draw(im)
and make sure the height of the new image is tall enough to accomodate the text.
import Image
import ImageDraw
im = Image.new("RGB", (200, 30), "#ddd")
draw = ImageDraw.Draw(im)
draw.text((10, 10), "run away", fill="red")
im.save("g.jpeg")
yields

please save with .jpg extention eg:
im.save("g.jpg")

Transparency with Python Image Library

I'm trying to place a PNG watermark with partial transparency on top of a Facebook profile pic (jpg) using the Python Image Library. The part that should be transparent simply comes off as white. Here's my code:
con = urllib2.urlopen('facebook_link_to_profile_pic')
im = Image.open(cStringIO.StringIO(con.read()))
overlayCon = urllib2.urlopen('link_to_overlay')
overlay = Image.open(cStringIO.StringIO(overlayCon.read()))
im.paste(overlay, (0, 0))
im.save('name', 'jpeg', quality=100)
I've tried a few different ways, but haven't gotten anything to work. Any help is appreciated.

The 3rd option to paste is a mask (see the docs). It accepts an RGBA image, so the simplest solution is to use your overlay image again: im.paste(overlay, (0, 0), overlay).