Resizing Tif's to smaller gifs adds pixels

[smullen.uclick@gmail.com]

I'm not entirely sure how this group works: if there is a page I'm
supposed to follow up on or if I should expect an email in reply.
Anyway, here's my question.

I'm very new to Python and PIL, I know how to do this stuff in perl
and ImageMagick, but I'm having issues with Python and PIL.

I need to scale a TIFF image from 1925x588 px to a GIF of 600xnnn px.

I've tried the following code, but it leads to a lot of extra odd
colored pixels being inserted into the resulting image.

img = "tmp/tmsho20080901.t if"
im = Image.open("tmp/tmsho20080901.t if")
w, h = im.size

im.thumbnail((6 00, h * 600 / w), Image.ANTIALIAS )

newimg = im.resize((600, int(h * (600.0 / w))), Image.ANTIALIAS )
newimg.save("tm sho20080901.gif ")

Using ImageMagick's convert I would do this...

convert -colors 256 -resize 600 -colorspace RGB -black-threshold 100 -
contrast -intent Perceptual tmp/tmsho20080901.t if tmsho20080901.g if

I think it may have something to do with the palette or the number of
colors alotted for the resulting image, but I'm really not a graphics
guy.

Any help on this would be appreciated.

Samuel

[Scott David Daniels]

Re: Resizing Tif's to smaller gifs adds pixels

smullen.uclick@ gmail.com wrote:

...I need to scale a TIFF image from 1925x588 px to a GIF of 600xnnn px.
I've tried the following code, but it leads to a lot of extra odd
colored pixels being inserted into the resulting image.

img = "tmp/tmsho20080901.t if"
im = Image.open("tmp/tmsho20080901.t if")
w, h = im.size
im.thumbnail((6 00, h * 600 / w), Image.ANTIALIAS )

This line is rather silly, making a result that you drop on the floor.

newimg = im.resize((600, int(h * (600.0 / w))), Image.ANTIALIAS )
newimg.save("tm sho20080901.gif ")

....

Using ImageMagick's convert I would do this...
>
convert -colors 256 -resize 600 -colorspace RGB -black-threshold 100 -
contrast -intent Perceptual tmp/tmsho20080901.t if tmsho20080901.g if
>
I think it may have something to do with the palette or the number of
colors alotted for the resulting image, but I'm really not a graphics
guy.

Yep, you are right. The issue is trying to reduce to a 256-color
pallette. Try using '.png' format (portable network graphics), that
allows a full palette for exact pixel images.

Try something like this:
im = Image.open("tmp/tmsho20080901.t if")
w, h = im.size
im.thumbnail((6 00, h * 600 // w),
Image.ANTIALIAS ).save("tmp/sho20080901.png ")

--Scott David Daniels
Scott.Daniels@A cm.Org

[Samuel]

Re: Resizing Tif's to smaller gifs adds pixels

Scott,

I appreciate the quick response, but I need this in a GIF format.

Samuel

On Oct 21, 3:46 pm, Scott David Daniels <Scott.Dani...@ Acm.Orgwrote:

smullen.ucl...@ gmail.com wrote:

...I need to scale a TIFF image from 1925x588 px to a GIF of 600xnnn px..
I've tried the following code, but it leads to a lot of extra odd
colored pixels being inserted into the resulting image.
img = "tmp/tmsho20080901.t if"
im = Image.open("tmp/tmsho20080901.t if")
w, h = im.size
im.thumbnail((6 00, h * 600 / w), Image.ANTIALIAS )

>
This line is rather silly, making a result that you drop on the floor.newimg = im.resize((600, int(h * (600.0 / w))), Image.ANTIALIAS )

newimg.save("tm sho20080901.gif ")

>
...
>

Using ImageMagick's convert I would do this...

>

convert -colors 256 -resize 600 -colorspace RGB -black-threshold 100 -
contrast -intent Perceptual tmp/tmsho20080901.t if tmsho20080901.g if

>

I think it may have something to do with the palette or the number of
colors alotted for the resulting image, but I'm really not a graphics
guy.

>
Yep, you are right.  The issue is trying to reduce to a 256-color
pallette.  Try using '.png' format (portable network graphics), that
allows a full palette for exact pixel images.
>
Try something like this:
     im = Image.open("tmp/tmsho20080901.t if")
     w, h = im.size
     im.thumbnail((6 00, h * 600 // w),
                  Image.ANTIALIAS ).save("tmp/sho20080901.png ")
>
--Scott David Daniels
Scott.Dani...@A cm.Org