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Image does not change when adding an alpha channel

3

The pillow package has a method called Image.putalpha() which is used to add or change the alpha channel of an image.

I tried to play with this method and found that I can not change the background color of an image. The original image is

This is my code to add alpha to it

from PIL import Image

im_owl = Image.open("owl.jpg")

alpha = Image.new("L", im_owl.size, 50)
im_owl.putalpha(alpha)

im_owl.show()

The produced image is nothing different from the original image. I have tried with different value of alpha and see no difference.

What could have been wrong?

python image image-processing python-imaging-library alpha

share|improve this question

edited 13 hours ago

jdhao

asked 13 hours ago

jdhaojdhao

4,34412445

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Aren't you suppose to first create the image with alpha channel? cv2.COLOR_RGB2RGBA
  
  – DirtyBit
  13 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You can read the doc about Image.putalpha(), which does not require image to be with an alpha channel before hand. There is no OpenCV involved in this question.
  
  – jdhao
  13 hours ago
  
  

  
  
  
  

add a comment | 

3

The pillow package has a method called Image.putalpha() which is used to add or change the alpha channel of an image.

I tried to play with this method and found that I can not change the background color of an image. The original image is

This is my code to add alpha to it

from PIL import Image

im_owl = Image.open("owl.jpg")

alpha = Image.new("L", im_owl.size, 50)
im_owl.putalpha(alpha)

im_owl.show()

The produced image is nothing different from the original image. I have tried with different value of alpha and see no difference.

What could have been wrong?

python image image-processing python-imaging-library alpha

share|improve this question

edited 13 hours ago

jdhao

asked 13 hours ago

jdhaojdhao

4,34412445

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Aren't you suppose to first create the image with alpha channel? cv2.COLOR_RGB2RGBA
  
  – DirtyBit
  13 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  You can read the doc about Image.putalpha(), which does not require image to be with an alpha channel before hand. There is no OpenCV involved in this question.
  
  – jdhao
  13 hours ago
  
  

  
  
  
  

add a comment | 

The pillow package has a method called Image.putalpha() which is used to add or change the alpha channel of an image.

I tried to play with this method and found that I can not change the background color of an image. The original image is

This is my code to add alpha to it

from PIL import Image

im_owl = Image.open("owl.jpg")

alpha = Image.new("L", im_owl.size, 50)
im_owl.putalpha(alpha)

im_owl.show()

The produced image is nothing different from the original image. I have tried with different value of alpha and see no difference.

What could have been wrong?

python image image-processing python-imaging-library alpha

share|improve this question

edited 13 hours ago

jdhao

asked 13 hours ago

jdhaojdhao

4,34412445

from PIL import Image

im_owl = Image.open("owl.jpg")

alpha = Image.new("L", im_owl.size, 50)
im_owl.putalpha(alpha)

im_owl.show()

share|improve this question

edited 13 hours ago

jdhao

asked 13 hours ago

jdhaojdhao

4,34412445

share|improve this question

edited 13 hours ago

jdhao

asked 13 hours ago

jdhaojdhao

4,34412445

asked 13 hours ago

jdhaojdhao

4,34412445

asked 13 hours ago

jdhaojdhao

4,34412445

2 Answers
2

active

oldest

votes

1

try to save the image and see it.
I am also not able to see the image directly from

im_owl.show()

but when I saved it

im_owl.save()

I am able to see the image changed.

share|improve this answer

answered 13 hours ago

sanyamsanyam

311

New contributor

sanyam is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

1

Try using

im_owl.save("alphadOwl.png")

And then view the saved image. It would seem that the alpha channel isn't applied to bmp or jpg files. It is a bmp file that gets displayed with im.show()

(For the record, I'm on a mac, I don't know if im.show() uses different applications on other devices).

share|improve this answer

answered 13 hours ago

PamPam

6911513

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks, it seems the image is shown as bmp file, which does not use alpha channel.
  
  – jdhao
  12 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Might be worth looking at what happens when you read it back in to a PIL image - does the alpha channel remain?
  
  – Pam
  11 hours ago
  

  
  
  
  

add a comment | 

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1

try to save the image and see it.
I am also not able to see the image directly from

im_owl.show()

but when I saved it

im_owl.save()

I am able to see the image changed.

share|improve this answer

answered 13 hours ago

sanyamsanyam

311

New contributor

sanyam is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

1

try to save the image and see it.
I am also not able to see the image directly from

im_owl.show()

but when I saved it

im_owl.save()

I am able to see the image changed.

share|improve this answer

answered 13 hours ago

sanyamsanyam

311

New contributor

sanyam is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

try to save the image and see it.
I am also not able to see the image directly from

im_owl.show()

but when I saved it

im_owl.save()

I am able to see the image changed.

share|improve this answer

answered 13 hours ago

sanyamsanyam

311

New contributor

sanyam is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

im_owl.show()

im_owl.save()

share|improve this answer

answered 13 hours ago

sanyamsanyam

311

New contributor

sanyam is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

answered 13 hours ago

sanyamsanyam

311

New contributor

sanyam is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

answered 13 hours ago

sanyamsanyam

311

1

Try using

im_owl.save("alphadOwl.png")

And then view the saved image. It would seem that the alpha channel isn't applied to bmp or jpg files. It is a bmp file that gets displayed with im.show()

(For the record, I'm on a mac, I don't know if im.show() uses different applications on other devices).

share|improve this answer

answered 13 hours ago

PamPam

6911513

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks, it seems the image is shown as bmp file, which does not use alpha channel.
  
  – jdhao
  12 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Might be worth looking at what happens when you read it back in to a PIL image - does the alpha channel remain?
  
  – Pam
  11 hours ago
  

  
  
  
  

add a comment | 

1

Try using

im_owl.save("alphadOwl.png")

And then view the saved image. It would seem that the alpha channel isn't applied to bmp or jpg files. It is a bmp file that gets displayed with im.show()

(For the record, I'm on a mac, I don't know if im.show() uses different applications on other devices).

share|improve this answer

answered 13 hours ago

PamPam

6911513

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Thanks, it seems the image is shown as bmp file, which does not use alpha channel.
  
  – jdhao
  12 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Might be worth looking at what happens when you read it back in to a PIL image - does the alpha channel remain?
  
  – Pam
  11 hours ago
  

  
  
  
  

add a comment | 

Try using

im_owl.save("alphadOwl.png")

And then view the saved image. It would seem that the alpha channel isn't applied to bmp or jpg files. It is a bmp file that gets displayed with im.show()

(For the record, I'm on a mac, I don't know if im.show() uses different applications on other devices).

share|improve this answer

answered 13 hours ago

PamPam

6911513

im_owl.save("alphadOwl.png")

share|improve this answer

answered 13 hours ago

PamPam

6911513

answered 13 hours ago

PamPam

6911513

answered 13 hours ago

PamPam

6911513