Re: [Matplotlib-users] PS and imshow
OK, I've got it. Previously, I checked the quality of the output image by two means: by visual inspection in gv and by checking the size of the output eps images. I was puzzled by the different sizes of the images at magnification 1. Also, convert produces much larger eps files. When the size of the output image is set to 6.3246cm (1494px at 600dpi) and the axes are turned off, both versions appear identical when printed. Thanks for your help, petr On Thu, 2007-08-30 at 20:35, Jouni K. Seppänen wrote: > I don't see a big difference between test-600.eps and test-convert.eps > when viewed in gv with magnification 10 and 0.1, respectively. Obviously > there is some resampling in test-600.eps: your source image is 1494 by > 1494 pixels large, which at 600 dpi is larger than the 5 by 5 cm figure > created by the script (and the axes are even smaller). test-convert.eps > has a bounding box of 0 0 1494 1494, so obviously it is a non-resampled > image at 72 dpi. > > If the problem you are alluding to is in the resampling, perhaps > varying the interpolation algorithm will produce a better result? > See the docstring of imshow. > > To get a non-resampled image, figimage should work, but it doesn't seem > to understand PIL images yet... - This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
Re: [Matplotlib-users] PS and imshow
Petr Danecek <[EMAIL PROTECTED]> writes:
> On Fri, 2007-08-24 at 20:03, Jouni K. Seppänen wrote:
>
>> savefig('foo10.ps', dpi=10)
>> savefig('foo100.ps', dpi=100)
>
> In fact, the dpi option does change the resulting PS file, but the
> quality is still very poor - see the example
> http://www.ucl.cas.cz/~petr/matplotlib-test.tgz
I don't see a big difference between test-600.eps and test-convert.eps
when viewed in gv with magnification 10 and 0.1, respectively. Obviously
there is some resampling in test-600.eps: your source image is 1494 by
1494 pixels large, which at 600 dpi is larger than the 5 by 5 cm figure
created by the script (and the axes are even smaller). test-convert.eps
has a bounding box of 0 0 1494 1494, so obviously it is a non-resampled
image at 72 dpi.
If the problem you are alluding to is in the resampling, perhaps
varying the interpolation algorithm will produce a better result?
See the docstring of imshow.
To get a non-resampled image, figimage should work, but it doesn't seem
to understand PIL images yet...
--
Jouni K. Seppänen
http://www.iki.fi/jks
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Re: [Matplotlib-users] PS and imshow
In fact, the dpi option does change the resulting PS file, but the
quality is still very poor - see the example
http://www.ucl.cas.cz/~petr/matplotlib-test.tgz
pd
On Fri, 2007-08-24 at 20:03, Jouni K. Seppänen wrote:
> I just tried with current svn, and the following script produces two
> results that have visibly different resolutions:
>
> #!/usr/bin/python
> from pylab import *
> foo = rand(10,10)
> imshow(foo)
> savefig('foo10.ps', dpi=10)
> savefig('foo100.ps', dpi=100)
>
> Perhaps the original poster could show a bit of code where the scaling
> fails?
>
> (I'm not sure if figimage is doing the right thing, though...)
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Re: [Matplotlib-users] PS and imshow
"John Hunter" <[EMAIL PROTECTED]> writes:
> On 8/24/07, Christopher Barker <[EMAIL PROTECTED]> wrote:
>
>> This may not be what it seems. The native coordinate system for
>> PostScript is in points, which are 1/72 if an inch, so it's common to
>> force that as a dpi. [...]
>
> Yes, this is exactly right and the reason we do it this way. We
> support fractional points so indeed you have higher resolutions. Off
> the top of my head, I am not sure what is going on with the image
> resolution problem
I just tried with current svn, and the following script produces two
results that have visibly different resolutions:
#!/usr/bin/python
from pylab import *
foo = rand(10,10)
imshow(foo)
savefig('foo10.ps', dpi=10)
savefig('foo100.ps', dpi=100)
Perhaps the original poster could show a bit of code where the scaling
fails?
(I'm not sure if figimage is doing the right thing, though...)
--
Jouni K. Seppänen
http://www.iki.fi/jks
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Re: [Matplotlib-users] PS and imshow
On 8/24/07, Christopher Barker <[EMAIL PROTECTED]> wrote: > This may not be what it seems. The native coordinate system for > PostScript is in points, which are 1/72 if an inch, so it's common to > force that as a dpi. Postscript supports fractional (is it floating > point or fixed -- I'm not sure) points, however, so you can define > things in higher resolution, and I'm pretty sure you can imbed an > arbitrary dpi image in a a PostScript file, using the 72dpi to positions > the image. Yes, this is exactly right and the reason we do it this way. We support fractional points so indeed you have higher resolutions. Off the top of my head, I am not sure what is going on with the image resolution problem JDH - This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
Re: [Matplotlib-users] PS and imshow
Petr Danecek wrote: > Hi, > I'd like to open a high-quality image (600dpi) in matplotlib, add some > plots and save it as a postscript file. > It seems that whatever I do, the input image gets scaled down > :-( I'm sorry I don't know enough about MPL's handling of images to help, but... > Looking in the code of matplotlib, there is a constant of 72dpi > hardwired everywhere. For instance, backend_ps.py there is the line > self.figure.dpi.set(72) # ignore the dpi kwarg This may not be what it seems. The native coordinate system for PostScript is in points, which are 1/72 if an inch, so it's common to force that as a dpi. Postscript supports fractional (is it floating point or fixed -- I'm not sure) points, however, so you can define things in higher resolution, and I'm pretty sure you can imbed an arbitrary dpi image in a a PostScript file, using the 72dpi to positions the image. The problem comes if the code, in addition to using 72dpi, also assumes integer coordinates, then you can't get better accuracy that 72dpi, which is not very good, and is really bad if someone scales it up later. wxWidgets addresses this by hard-coding 720dpi, rather than 72, and dividing by ten when writing the postscript -- still a bit of kludge. I'm not sure what MPL does. -Chris -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/OR&R(206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception [EMAIL PROTECTED] - This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
[Matplotlib-users] PS and imshow
Hi, I'd like to open a high-quality image (600dpi) in matplotlib, add some plots and save it as a postscript file. It seems that whatever I do, the input image gets scaled down :-( The same question was asked year ago. Has any progress been made since then? http://sourceforge.net/mailarchive/message.php?msg_id=200608311227.30594.dd55%40cornell.edu Looking in the code of matplotlib, there is a constant of 72dpi hardwired everywhere. For instance, backend_ps.py there is the line self.figure.dpi.set(72) # ignore the dpi kwarg Would rising of this value to 600 help? No offence to developers, I did not even try to understand the code, but using the number 72 instead of using a variable seems to be a bad programming practice to me. Petr Danecek - This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ ___ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
