Hi,
I've just moved from MATLAB to matplotlib, and I'm really impressed
with the quality of the PS figures it generates with usetex and the
xpdf distiller. I've hit a couple of problems though, one I've manged
to solve (patch against 0.87.4 attached) and the other I'd be greatful
if you could help me with please.
I've been using imshow to basically put a set of axes round an image
produced my simulation code. Here's a minimal version of my script:
----------------------------------------------
from pylab import *
rc('text', usetex=True)
rc('ps', usedistiller="xpdf")
figure(1,figsize=(6, 4))
im=imread('image.png') # a 301x318 image
imshow(im,interpolation='nearest',extent=[0.98, 20, 0.01, 0.5])
axis('normal');
savefig('image.eps')
--------------------------------------------
The first problem I noticed is that the distilling process was causing
some of my images to have (lossy) compression applied and others not.
It turns out that it is a feature of ps2pdf that it tries to detect
the content of the image and apply appropriate compression. You can
over ride this distiller options. My patch adds a new rc option
ps.image_compression that can be set to auto (preserves the current
behaviour), DCTEncode (applies lossy JPEG compression), and
FlateEncode (lossless compression). The distiller commands are
embedded in the ps file. I looked at making it a flag on each image,
but couldn't get it to work. Another way to do it is to pass extra
command line options to ps2pdf (-dAutoFilterColorImages=false
-sColorImageFilter=FlateEncode should do it for colour images). I
thought embedding it in the PS file would be more flexible.
My second problem involved the resolutions of the image. I'd like to
preserve the resolution of my image in the PS output, but I can't
figure out how to stop the image being resized and interpolated.
Obviously you need to do this for the bitmap backends, but for vector
ones surely you can just scale the original image in the vector
output.
Thanks in advance for you help and some great software!
JIM
---
On Thursday 27 July 2006 8:33 am, JIM MacDonald wrote: > Hi, > > I've just moved from MATLAB to matplotlib, and I'm really impressed > with the quality of the PS figures it generates with usetex and the > xpdf distiller. Glad to hear it. > I've hit a couple of problems though [...] > The first problem I noticed is that the distilling process was causing > some of my images to have (lossy) compression applied and others not. > It turns out that it is a feature of ps2pdf that it tries to detect > the content of the image and apply appropriate compression. You can > over ride this distiller options. My patch adds a new rc option > ps.image_compression that can be set to auto (preserves the current > behaviour), DCTEncode (applies lossy JPEG compression), and > FlateEncode (lossless compression). The distiller commands are > embedded in the ps file. I looked at making it a flag on each image, > but couldn't get it to work. Another way to do it is to pass extra > command line options to ps2pdf (-dAutoFilterColorImages=false > -sColorImageFilter=FlateEncode should do it for colour images). I > thought embedding it in the PS file would be more flexible. I'll look into this soon. I'm hesitant to add another rc option, maybe we can consider using these settings as the defaults. I'll post again after I have had a chance to play with it. > My second problem involved the resolutions of the image. I'd like to > preserve the resolution of my image in the PS output, but I can't > figure out how to stop the image being resized and interpolated. > Obviously you need to do this for the bitmap backends, but for vector > ones surely you can just scale the original image in the vector > output. The resolution for Postscript is 72 dpi, and I'm not sure this can be changed. Would you send me an example postscript file along with the original png?
On Thu, Jul 27, 2006 at 01:33:42PM +0100, JIM MacDonald wrote: > Another way to do it is to pass extra > command line options to ps2pdf (-dAutoFilterColorImages=3Dfalse > -sColorImageFilter=3DFlateEncode should do it for colour images). I > thought embedding it in the PS file would be more flexible. +1 for that. I am having exactly the same problem. --=20 Ga=EBl
> I'll look into this soon. I'm hesitant to add another rc option, maybe we can > consider using these settings as the defaults. I'll post again after I have > had a chance to play with it. Defaulting to lossless FlateEncode compression seems like a good idea, if the file is too big you can always run another distill cycle after wards manually. Another possibility would be to set the option based on the format of the image loaded (I'm sure I read somewhere that it is planned to support formats other than PNG). ie FlateEncode for GIF's and PNG's and DCTEncode for JPEG's. > The resolution for Postscript is 72 dpi, and I'm not sure this can be changed. > Would you send me an example postscript file along with the original png? Sure, http://jimmacdonald.co.uk/matplotlib/image.png http://jimmacdonald.co.uk/matplotlib/image.eps http://jimmacdonald.co.uk/matplotlib/image.py image.py generates image.eps from image.png. image.png is simple enough for ps2pdf not to use DCT encoding. Looking at the postscript shows that the image has resolution of 335x230 compared to the original of 318x301. JIM ---
On Monday 31 July 2006 09:32, JIM MacDonald wrote: > > The resolution for Postscript is 72 dpi, and I'm not sure this can be > > changed. Would you send me an example postscript file along with the > > original png? > > Sure, > http://jimmacdonald.co.uk/matplotlib/image.png > http://jimmacdonald.co.uk/matplotlib/image.eps > http://jimmacdonald.co.uk/matplotlib/image.py > > image.py generates image.eps from image.png. image.png is simple > enough for ps2pdf not to use DCT encoding. Looking at the postscript > shows that the image has resolution of 335x230 compared to the > original of 318x301. I don't think this is a problem with the postscript backend. You're rescaling the image in your script. Try something like this: from pylab import * rc('text', usetex=True) rc('ps', usedistiller="xpdf") figure(1,figsize=(6, 4)) im=imread('image.png') imshow(im,interpolation='nearest')#,extent=[0.98, 20, 0.01, 0.5]) #axis('normal'); savefig('image.eps') Darren
> I don't think this is a problem with the postscript backend. You're rescaling
> the image in your script. Try something like this:
>
> from pylab import *
>
> rc('text', usetex=True)
> rc('ps', usedistiller="xpdf")
>
> figure(1,figsize=(6, 4))
> im=imread('image.png')
> imshow(im,interpolation='nearest')#,extent=[0.98, 20, 0.01, 0.5])
> #axis('normal');
> savefig('image.eps')
I just tried that and it still rescales the image, this time to
243x230. I've found I can use the figsize kwarg to control the
resolution of the embedded image, but of course this means I can't
have the figure the size I want it.
JIM
---
On Monday 31 July 2006 09:32, JIM MacDonald wrote: > > I'll look into this soon. I'm hesitant to add another rc option, maybe we > > can consider using these settings as the defaults. I'll post again after > > I have had a chance to play with it. > > Defaulting to lossless FlateEncode compression seems like a good idea, > if the file is too big you can always run another distill cycle after > wards manually. > > Another possibility would be to set the option based on the format of > the image loaded (I'm sure I read somewhere that it is planned to > support formats other than PNG). ie FlateEncode for GIF's and PNG's > and DCTEncode for JPEG's. [...] > Sure, > http://jimmacdonald.co.uk/matplotlib/image.png > http://jimmacdonald.co.uk/matplotlib/image.eps > http://jimmacdonald.co.uk/matplotlib/image.py > > image.py generates image.eps from image.png. image.png is simple > enough for ps2pdf not to use DCT encoding. Looking at the postscript > shows that the image has resolution of 335x230 compared to the > original of 318x301. Would you post an example where the ps2pdf flags make a big difference on the output? I just tried with the above png, but I cant tell the difference between the results with/without the new flags. Darren
> Would you post an example where the ps2pdf flags make a big difference on the > output? I just tried with the above png, but I cant tell the difference > between the results with/without the new flags. http://jimmacdonald.co.uk/matplotlib/MPD_SinPulse_g0.500.png JIM ---
On Mon, Jul 31, 2006 at 10:01:23AM -0400, Darren Dale wrote: > Would you post an example where the ps2pdf flags make a big difference = on the=20 > output? I just tried with the above png, but I cant tell the difference= =20 > between the results with/without the new flags. Last image of http://scipy.org/GaelVaroquaux, the example script. You can also have a look at the "pylab2pdf2 script, where I use environmental variables to get a proper behaviour from GS and avoid this problem. --=20 Ga=EBl
On Monday 31 July 2006 10:05, Gael Varoquaux wrote: > On Mon, Jul 31, 2006 at 10:01:23AM -0400, Darren Dale wrote: > > Would you post an example where the ps2pdf flags make a big difference on > > the output? I just tried with the above png, but I cant tell the > > difference between the results with/without the new flags. > > Last image of http://scipy.org/GaelVaroquaux, the example script. You > can also have a look at the "pylab2pdf2 script, where I use > environmental variables to get a proper behaviour from GS and avoid this > problem. I see. Thanks for pointing this out and providing the solution. The flags you suggested are passed to ps2pdf as of svn 2639. Darren
On Mon, Jul 31, 2006 at 10:19:46AM -0400, Darren Dale wrote: > I see. Thanks for pointing this out and providing the solution. The fla= gs you=20 > suggested are passed to ps2pdf as of svn 2639. Great ! Thanks. I like open source software so much because of these little details :->. --=20 Ga=EBl
>>>>> "JIM" == JIM MacDonald <ji...@ji...> writes: JIM> My second problem involved the resolutions of the image. I'd JIM> like to preserve the resolution of my image in the PS output, JIM> but I can't figure out how to stop the image being resized JIM> and interpolated. Obviously you need to do this for the There are two kinds of images in matplotlib -- AxesImage and FigureImage. By definition, the AxesImage is interpolated to fit into the Axes box. You can control the aspect ratio of the interpolation, but it will be interpolated. FigureImage, on the other hand, performs a pixel dump to the postscript canvas at the location you tell it to -- see examples/figimage_demo.py. It should like you are more interested in the latter. If the figure image doesn't work for you, describe your use-case in some detail and why neither work and we'll see if we can accommodate it. JDH
> There are two kinds of images in matplotlib -- AxesImage and > FigureImage. By definition, the AxesImage is interpolated to fit into > the Axes box. You can control the aspect ratio of the interpolation, > but it will be interpolated. FigureImage, on the other hand, performs > a pixel dump to the postscript canvas at the location you tell it to > -- see examples/figimage_demo.py. It should like you are more > interested in the latter. I've had a play with FigureImage and I can't see how to make it draw the image inside the axes, it seems to only draw it in the background. > If the figure image doesn't work for you, describe your use-case in > some detail and why neither work and we'll see if we can accommodate > it. OK, so imshow does exactly what I want. The only problem is the resampling. Each pixel represents a value calculated at a point on a 318x301 grid, so in resampling I loose or distort some of the fine detail. I do not understand why the image need to be resampled when using a vector based backend. I understand this is necessary for a raster backend, but surely with a vector backend you can just scale the image keeping the 318x301 resolution. I know this is possible in Postscript at least as I've produced the desired output by amalgamating two files. See http://jimmacdonald.co.uk/matplotlib/image_CORRECT_ps_hacked.eps I looked at using pcolor instead, but the postscript files where too big (~20MB) due to the large number of tiles (this is how I used to do it in matlab). JIM ----
