Hello I have a numpy array that I obtained from a converted RGBA gif image. I have tried to replace some colours with different ones using the where condition but have a problem with dimensions.
If I use b=where(a==0,255,a) where a is a numpy array from an image it does replace components of the RGB values in each pixel but it fails if I try b=where(a==(0,0,0,255),(255,255,255,255),a) with incorrect dimension error. Could you please help? Thanks Frank -----Original Message----- From: numpy-discussion-boun...@scipy.org [mailto:numpy-discussion-boun...@scipy.org] On Behalf Of numpy-discussion-requ...@scipy.org Sent: 10 April 2009 08:18 To: numpy-discussion@scipy.org Subject: Numpy-discussion Digest, Vol 31, Issue 24 Send Numpy-discussion mailing list submissions to numpy-discussion@scipy.org To subscribe or unsubscribe via the World Wide Web, visit http://mail.scipy.org/mailman/listinfo/numpy-discussion or, via email, send a message with subject or body 'help' to numpy-discussion-requ...@scipy.org You can reach the person managing the list at numpy-discussion-ow...@scipy.org When replying, please edit your Subject line so it is more specific than "Re: Contents of Numpy-discussion digest..." Today's Topics: 1. Re: DVCS at PyCon (Ondrej Certik) 2. Re: using reducing functions without eliminating dimensions? (Dan Lenski) 3. Re: Another Array (Ian Mallett) 4. Re: Another Array (Robert Kern) 5. Re: Another Array (Ian Mallett) 6. Re: Another Array (Robert Kern) 7. Re: Another Array (Ian Mallett) 8. Re: Another Array (Anne Archibald) ---------------------------------------------------------------------- Message: 1 Date: Thu, 9 Apr 2009 23:14:53 -0700 From: Ondrej Certik <ond...@certik.cz> Subject: Re: [Numpy-discussion] DVCS at PyCon To: Discussion of Numerical Python <numpy-discussion@scipy.org> Message-ID: <85b5c3130904092314o7512cdbfjd2f43b98e65f4...@mail.gmail.com> Content-Type: text/plain; charset=UTF-8 On Thu, Apr 9, 2009 at 10:45 PM, David Cournapeau <da...@ar.media.kyoto-u.ac.jp> wrote: > Ondrej Certik wrote: >> >> It is maybe easier to learn how to work with different clones, but >> once you start working with lots of patches and you need to reclone >> all the time, then it's the wrong approach to work, as it takes lots >> of time to copy the whole repository on the disk. > > Yes, *I* know how to use git, and I agree with you, I vastly prefer git > branch handling to bzr branch handling. *I* find working with GUI for > VCS a real PITA. But I am not the only numpy developer, that's why the > feedback from people like Josef with a totally different workflow than > me is valuable - much more than people like us who are unix geeks :) Yes, definitely. Ondrej ------------------------------ Message: 2 Date: Fri, 10 Apr 2009 06:36:08 +0000 (UTC) From: Dan Lenski <dlen...@gmail.com> Subject: Re: [Numpy-discussion] using reducing functions without eliminating dimensions? To: numpy-discussion@scipy.org Message-ID: <grmpcn$2j...@ger.gmane.org> Content-Type: text/plain; charset=UTF-8 On Thu, 09 Apr 2009 01:31:33 -0500, Robert Kern wrote: > On Thu, Apr 9, 2009 at 01:29, Anne Archibald <peridot.face...@gmail.com> > wrote: > >> What's wrong with np.amin(a,axis=-1)[...,np.newaxis]? > > It's cumbersome, particularly when you have axis=arbitrary_axis. Quite right. It would nice to be able to say: np.amin(a, axiskeep=-1) or a.min(axiskeep=3) ... or something along those lines. Dan ------------------------------ Message: 3 Date: Thu, 9 Apr 2009 23:42:03 -0700 From: Ian Mallett <geometr...@gmail.com> Subject: Re: [Numpy-discussion] Another Array To: Discussion of Numerical Python <numpy-discussion@scipy.org> Message-ID: <a62fab400904092342y5509976bk927277d72730a...@mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1" It gives a perfect parabolic shape that looks very nice, but somewhat unrealistic. I'd like to scale the unit vectors by a random length (which can just be a uniform distribution). I tried scaling the unit vector n*n*3 array by a random n*n array, but that didn't work, obviously. Help? -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mail.scipy.org/pipermail/numpy-discussion/attachments/20090409/e8fea8 42/attachment-0001.html ------------------------------ Message: 4 Date: Fri, 10 Apr 2009 01:46:47 -0500 From: Robert Kern <robert.k...@gmail.com> Subject: Re: [Numpy-discussion] Another Array To: Discussion of Numerical Python <numpy-discussion@scipy.org> Message-ID: <3d375d730904092346l6850c03chca1962915263e...@mail.gmail.com> Content-Type: text/plain; charset=UTF-8 On Fri, Apr 10, 2009 at 01:42, Ian Mallett <geometr...@gmail.com> wrote: > It gives a perfect parabolic shape that looks very nice, but somewhat > unrealistic. Parabolic? They should be spherical. > I'd like to scale the unit vectors by a random length (which > can just be a uniform distribution).? I tried scaling the unit vector n*n*3 > array by a random n*n array, but that didn't work, obviously. No, it's not obvious. Exactly what code did you try? What results did you get? What results were you expecting? > Help? Let's take a step back. What kind of distribution are you trying to achieve? You asked for uniformly distributed unit vectors. Now you are asking for something else, but I'm really not sure what. What standard are you comparing against when you say that the unit vectors look "unrealistic"? -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco ------------------------------ Message: 5 Date: Thu, 9 Apr 2009 23:58:21 -0700 From: Ian Mallett <geometr...@gmail.com> Subject: Re: [Numpy-discussion] Another Array To: Discussion of Numerical Python <numpy-discussion@scipy.org> Message-ID: <a62fab400904092358m60233289u73aba89a6bdad...@mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1" On Thu, Apr 9, 2009 at 11:46 PM, Robert Kern <robert.k...@gmail.com> wrote: > Parabolic? They should be spherical. The particle system in the last screenshot was affected by gravity. In the absence of gravity, the results should be spherical, yes. All the vectors are a unit length, which produces a perfectly smooth surface (unrealistic for such an effect). > No, it's not obvious. Exactly what code did you try? What results did > you get? What results were you expecting? It crashed. I have this code: vecs = Numeric.random.standard_normal(size=(self.size[0],self.size[1],3)) magnitudes = Numeric.sqrt((vecs*vecs).sum(axis=-1)) uvecs = vecs / magnitudes[...,Numeric.newaxis] randlen = Numeric.random.random((self.size[0],self.size[1])) randuvecs = uvecs*randlen #It crashes here with a dimension mismatch rgb = ((randvecs+1.0)/2.0)*255.0 I also tried randlen = Numeric.random.random((self.size[0],self.size[1],3)), but this does not scale each of the vector's components equally, producing artifacts again. Each needs to be scaled by the same random value for it to make sense. > Let's take a step back. What kind of distribution are you trying to > achieve? You asked for uniformly distributed unit vectors. Now you are > asking for something else, but I'm really not sure what. What standard > are you comparing against when you say that the unit vectors look > "unrealistic"? The vectors are used to "jitter" each particle's initial speed, so that the particles go in different directions instead of moving all as one. Using the unit vector causes the particles to make the smooth parabolic shape. The jitter vectors much then be of a random length, so that the particles go in all different directions at all different speeds, instead of just all in different directions. Ian -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mail.scipy.org/pipermail/numpy-discussion/attachments/20090409/8d6bd9 31/attachment-0001.html ------------------------------ Message: 6 Date: Fri, 10 Apr 2009 02:01:10 -0500 From: Robert Kern <robert.k...@gmail.com> Subject: Re: [Numpy-discussion] Another Array To: Discussion of Numerical Python <numpy-discussion@scipy.org> Message-ID: <3d375d730904100001w4cdb7bedi2b36bca97731e...@mail.gmail.com> Content-Type: text/plain; charset=UTF-8 On Fri, Apr 10, 2009 at 01:58, Ian Mallett <geometr...@gmail.com> wrote: > On Thu, Apr 9, 2009 at 11:46 PM, Robert Kern <robert.k...@gmail.com> wrote: >> >> Parabolic? They should be spherical. > > The particle system in the last screenshot was affected by gravity.? In the > absence of gravity, the results should be spherical, yes.? All the vectors > are a unit length, which produces a perfectly smooth surface (unrealistic > for such an effect). >> >> No, it's not obvious. Exactly what code did you try? What results did >> you get? What results were you expecting? > > It crashed. > I have this code: > vecs = Numeric.random.standard_normal(size=(self.size[0],self.size[1],3)) > magnitudes = Numeric.sqrt((vecs*vecs).sum(axis=-1)) > uvecs = vecs / magnitudes[...,Numeric.newaxis] > randlen = Numeric.random.random((self.size[0],self.size[1])) > randuvecs = uvecs*randlen #It crashes here with a dimension mismatch > rgb = ((randvecs+1.0)/2.0)*255.0 > > I also tried randlen = Numeric.random.random((self.size[0],self.size[1],3)), > but this does not scale each of the vector's components equally, producing > artifacts again.? Each needs to be scaled by the same random value for it to > make sense. See how I did magnitudes[...,numpy.newaxis]? You have to do the same. >> Let's take a step back. What kind of distribution are you trying to >> achieve? You asked for uniformly distributed unit vectors. Now you are >> asking for something else, but I'm really not sure what. What standard >> are you comparing against when you say that the unit vectors look >> "unrealistic"? > > The vectors are used to "jitter" each particle's initial speed, so that the > particles go in different directions instead of moving all as one.? Using > the unit vector causes the particles to make the smooth parabolic shape. > The jitter vectors much then be of a random length, so that the particles go > in all different directions at all different speeds, instead of just all in > different directions. Ah, okay. That makes sense. -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco ------------------------------ Message: 7 Date: Fri, 10 Apr 2009 00:07:45 -0700 From: Ian Mallett <geometr...@gmail.com> Subject: Re: [Numpy-discussion] Another Array To: Discussion of Numerical Python <numpy-discussion@scipy.org> Message-ID: <a62fab400904100007y185a80d5jfa4d62a850d1...@mail.gmail.com> Content-Type: text/plain; charset="iso-8859-1" This seems to work: vecs = Numeric.random.standard_normal(size=(self.size[0],self.size[1],3)) magnitudes = Numeric.sqrt((vecs*vecs).sum(axis=-1)) uvecs = vecs / magnitudes[...,Numeric.newaxis] randlen = Numeric.random.random((self.size[0],self.size[1])) randuvecs = uvecs*randlen[...,Numeric.newaxis] rgb = ((randuvecs+1.0)/2.0)*255.0 (I have "import numpy as Numeric" for other reasons, that's why there's Numeric there). Thanks, Ian -------------- next part -------------- An HTML attachment was scrubbed... URL: http://mail.scipy.org/pipermail/numpy-discussion/attachments/20090410/84e6aa a1/attachment-0001.html ------------------------------ Message: 8 Date: Fri, 10 Apr 2009 03:17:58 -0400 From: Anne Archibald <peridot.face...@gmail.com> Subject: Re: [Numpy-discussion] Another Array To: Discussion of Numerical Python <numpy-discussion@scipy.org> Message-ID: <ce557a360904100017l45019b89t32ce233226c4f...@mail.gmail.com> Content-Type: text/plain; charset=UTF-8 2009/4/10 Ian Mallett <geometr...@gmail.com>: > The vectors are used to "jitter" each particle's initial speed, so that the > particles go in different directions instead of moving all as one.? Using > the unit vector causes the particles to make the smooth parabolic shape. > The jitter vectors much then be of a random length, so that the particles go > in all different directions at all different speeds, instead of just all in > different directions. Why not just skip the normalization? Then you'll get vectors with random direction and a natural distribution of lengths. And it'll be faster than tne unit vectors... Anne ------------------------------ _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion End of Numpy-discussion Digest, Vol 31, Issue 24 ************************************************ _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
