Re: [Image-SIG] Help with PIL, Imagemagick Composite function in PIL?
On 4/11/07, Douglas Bagnall <[EMAIL PROTECTED]> wrote:
> Alexey, I think you are completely right about the problem, but the
> solution can be quite a bit simpler:
>
> dtop = Image.open("dtop.png")
> frame = Image.open("frame.png")
>
> dtop.paste(frame.convert('RGB'), (0,0), frame)
> dtop.save("test.png")
Hmm... The good part I see in this solution is that when image is
converted from RGBA to RGB it just so happens that its pixelsize is
still 4 but 4th byte is filled with 255. Then paste_mask_RGBA kicks
in, and if dtop has alpha channel it will composite its alpha channel
with 255, decreasing dtop transparency where frame is not completely
transparent. To be honest I'm not sure what is generally expected in
this situation, though looking at the way antigrain does rgba blending
I see that it essentially has this formula:
a = a * (1 - alpha) + 1 * alpha
Which is just the way it works in the code above (and absolutely not
the way it'd worked in my code). So if this behavior is expected my
example wouldn't even work as it should, thanks for showing that. :)
Best regards,
Alexey.
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Re: [Image-SIG] Help with PIL, Imagemagick Composite function in PIL?
Thanks to both of you and yes I was expecting the paste function to work
just like a paste in any Image Editor.
César
On Wed, 2007-04-11 at 11:48 +1200, Douglas Bagnall wrote:
> Alexey Borzenkov wrote:
>
> > The problem you have happens because alpha channel of images *also*
> > gets composited using the mask you specified. To do it right you
> > actually need to split image, save target image alpha channel and
> > after compositing merge it back using original alpha channel:
>
> Alexey, I think you are completely right about the problem, but the
> solution can be quite a bit simpler:
>
> dtop = Image.open("dtop.png")
> frame = Image.open("frame.png")
>
> dtop.paste(frame.convert('RGB'), (0,0), frame)
> dtop.save("test.png")
>
>
> I would say that this alpha-merging quirk comes close to being a bug --
> it's probably not what most people expect.
>
> douglas
>
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Re: [Image-SIG] Help with PIL, Imagemagick Composite function in PIL?
Alexey Borzenkov wrote:
> The problem you have happens because alpha channel of images *also*
> gets composited using the mask you specified. To do it right you
> actually need to split image, save target image alpha channel and
> after compositing merge it back using original alpha channel:
Alexey, I think you are completely right about the problem, but the
solution can be quite a bit simpler:
dtop = Image.open("dtop.png")
frame = Image.open("frame.png")
dtop.paste(frame.convert('RGB'), (0,0), frame)
dtop.save("test.png")
I would say that this alpha-merging quirk comes close to being a bug --
it's probably not what most people expect.
douglas
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Re: [Image-SIG] Help with PIL, Imagemagick Composite function in PIL?
On 4/10/07, César Pérez <[EMAIL PROTECTED]> wrote:
> Hi,
> I am new to this list but and i have a small problem with PIL.
>
> I am looking for a function that works like composite does in
> imagemagick.
[..snip..]
> from PIL import Image
>
> dtop = Image.open("dtop.png")
> frame = Image.open("frame.png")
>
> dtop.paste(frame,(0,0),frame)
> dtop.save("test.png")
>
> I tried every form of paste but I always get this result or worst.
The problem you have happens because alpha channel of images *also*
gets composited using the mask you specified. To do it right you
actually need to split image, save target image alpha channel and
after compositing merge it back using original alpha channel:
from PIL import Image
dtop = Image.open("dtop.png")
frame = Image.open("frame.png")
assert dtop.mode == "RGBA"
r,g,b,a = dtop.split()
dtop = Image.merge("RGB", (r,g,b))
dtop.paste(frame,(0,0),frame)
r,g,b = dtop.split()
dtop = Image.merge("RGBA", (r,g,b,a))
dtop.save("test.png")
Best regards,
Alexey.
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[Image-SIG] Help with PIL, Imagemagick Composite function in PIL?
Hi,
I am new to this list but and i have a small problem with PIL.
I am looking for a function that works like composite does in
imagemagick. If you don't know, composite puts the first image above the
second one and it's like pasting.
I have tried PIL paste but I can't get it to work as I want, specially
if my images have alpha channels.
For example I have an example script:
from PIL import Image
dtop = Image.open("dtop.png")
frame = Image.open("frame.png")
dtop.paste(frame,(0,0),frame)
dtop.save("test.png")
I tried every form of paste but I always get this result or worst.
Using the images from [1] the output image is different, I uploaded the
output file created by IM and PIL to [1] and as you can see it's not the
same. Imagemagick output is im.png and PIL is pil.png.
You can clearly see the difference if you put the images against a
background color other than white or by opening in something like GIMP
or any viewer that shows a checker pattern to represent the
transparency.
Imagemagick does it as I want but PIL doesn't.
I hope somebody can help or knows how to do it because I prefer using
only PIL as it's the only thing that I don't know how to do without
Imagemagick.
1. http://www.capc-online.net/images/temp/
THX
César Pérez
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