Thanks Eric and also Ryan, interpolation='nearest' worked. Maybe if the correct person is listening, this could be highlighted in the imshow documentation since the default of interpolation=none is not doing 'nothing' IMHO.
Also, I have looked > http://matplotlib.sourceforge.net/examples/pylab_examples/contour_image.html This highlights the various issues nicely. I noticed that the contourf example has white space at the top. Also, the use of arange(-3.0, 4.001, delta) implies some subtle work around may be needed. thanks On Wed, 2 Sep 2009, Eric Firing wrote: > Date: Wed, 02 Sep 2009 15:08:49 -1000 > From: Eric Firing <efir...@hawaii.edu> > To: Richard McMahon <r...@ast.cam.ac.uk> > Cc: matplotlib-users@lists.sourceforge.net > Subject: Re: [Matplotlib-users] imshow and pcolor differences > > Richard McMahon wrote: >> Hello, >> >> I want to display some data as an image and also as a contour. >> >> I have been looking at imshow and pcolor and find that contour >> and imshow are behaving differently than pcolor. In the example below I >> have a 5x5 image. pshow displays the pixels but imshow and contour shows >> resampling artifacts since they resample offset by 0.5pixels. >> >> The advantage of imshow is that the pixels are square which is what I >> want. I also want to use contour which also seems to show the same >> type of resampling as imshow. > > This is not a matter of resampling (unless I am misunderstanding you)--it is > a difference in the grid. For imshow and contour, the data points and the > grid intersections coincide; for pcolor (and pcolormesh), the grid gives the > boundaries of colored quadrilaterals. Therefore, if the data array is MxN, > then the the grid X dimension should be N+1 and the grid Y dimension should > be M+1. > > For an example of how to use contours with images, see: > > http://matplotlib.sourceforge.net/examples/pylab_examples/contour_image.html > > Also, it sounds like maybe you don't want imshow to interpolate: try using > the interpolation='nearest' kwarg. > > If you do want to use pcolor or pcolormesh or Axes.pcolorfast, then you can > still get square pixels by suitable choice of aspect ratio. Try > axis('equal') or axis('scaled'), or axis('image'), or use the set_aspect() > method of the Axes instance. > > Eric > >> >> import numpy as np >> import matplotlib as mpl >> import matplotlib.pyplot as plt >> >> image = np.random.rand(5,5) >> >> plt.figure() >> plt.pcolor(image) >> plt.title('pcolor defaults') >> >> plt.figure() >> plt.imshow(image, origin='lower') >> plt.title('imshow defaults with origin=lower') >> >> plt.show() >> >> Is there a method to force imshow to not resample the image >> It is not obvius to me from reading the help for imshow and pcolor. >> >> >> Thanks, richard >> >> ------------------------------------------------------------------- >> Dr. Richard G. McMahon | Phone (office) 44-(0)-1223-337519 >> University of Cambridge | (switchboard) 1223-337548 >> Institute of Astronomy | (secretary) 1223-337516 >> Madingley Rd | FAX 1223-337523 >> Cambridge, CB3 OHA, UK. | mobile 7885-409019 >> Office: Hoyle 18 | home 1223-359770 >> ------------------------------------------------------------------- >> email: r...@ast.cam.ac.uk | WWW: http://www.ast.cam.ac.uk/~rgm >> richardgmcma...@gmail.com | skype: richardgmcmahon >> ------------------------------------------------------------------- >> >> >> ------------------------------------------------------------------------------ >> Let Crystal Reports handle the reporting - Free Crystal Reports 2008 >> 30-Day trial. Simplify your report design, integration and deployment - >> and focus on what you do best, core application coding. Discover what's >> new with Crystal Reports now. http://p.sf.net/sfu/bobj-july >> _______________________________________________ >> Matplotlib-users mailing list >> Matplotlib-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/matplotlib-users > -- ------------------------------------------------------------------- Dr. Richard G. McMahon | Phone (office) 44-(0)-1223-337519 University of Cambridge | (switchboard) 1223-337548 Institute of Astronomy | (secretary) 1223-337516 Madingley Rd | FAX 1223-337523 Cambridge, CB3 OHA, UK. | mobile 7885-409019 Office: Hoyle 18 | home 1223-359770 ------------------------------------------------------------------- email: r...@ast.cam.ac.uk | WWW: http://www.ast.cam.ac.uk/~rgm richardgmcma...@gmail.com | skype: richardgmcmahon ------------------------------------------------------------------- ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ Matplotlib-users mailing list Matplotlib-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/matplotlib-users
