Thanks JJ. The problem seems not to be a size issue -- markersize has no effect when use marker="," (pixel). I have also tried to turn off aa, and it doesn't help either. I also tried different backends. The PNG output from Agg and Cairo is slightly different: Agg's point has 4 solid pixel, while Cairo's has 4 pixel with random shade.
Postscript output has the same problem. The "pixel" in an EPS file
generated by mpl is significantly bigger than that from another
drawing program I used.
The problem occurs in all my plotting scripts, e.g., this basic one:
[CODE]
import numpy as np
x=np.arange(100)
y=np.random.randn(100)
ioff()
fig=gcf()
fig.clf()
ax=fig.add_axes(0.15,0.1,0.8, 0.85)
ax.plot(x,y,"k,")
ion()
fig.canvas.draw()
[/CODE]
Here is how I identify the problem:
1. use the above script to plot on screen
2. savefig("plot.png")
3. open plot.png in GIMP and check the pixel size.
I also attached the two PNG files generated with Agg and Cairo backends.
On Sun, Feb 5, 2012 at 6:45 AM, Jae-Joon Lee <lee.j.j...@gmail.com> wrote:
> How are you plotting your points.
>
> If you use *plot*, there is a *markersize* parameter.
> If you use *scatter*, the third argument controls the marker size.
>
> But you may actually complaining about other issues, e.g.,
> antialiasing, etc. So, if above are not your answer, please post a
> complete example and describe your problem in more detail.
>
> Regards,
>
> -JJ
>
>
> On Sat, Feb 4, 2012 at 2:15 PM, Chris <plut...@gmail.com> wrote:
>> I noticed this a few years back, but left it aside because most of the
>> time I can live with it. Recently I need to make a few plots
>> containing a few million points, and 4 pixels for a point is a
>> disaster. So my question is why the pixel marker size is set at 4
>> pixels? And is there anyway to change it to a single pixel?
>>
>> Thanks,
>> Chris
>>
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<<attachment: plot.agg.png>>
<<attachment: plot.cairo.png>>
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