Thanks. Now I understand the situation.
As far as I can see, marker="," is implemented as a rectangle path
with width/height of 1 pixel, so this result in 2x2 pixel filled
square.
I tried to change the size of the rectangle, etc, to get a single
pixel filled square, but did not get a satisfactory result.
I think we need an Agg expert. I hope Mike or others take a look.
Chris,
if you do not get a response from others in this mailing list, I
recommend you to open a new issue in our github page.
Regards,
-JJ
On Mon, Feb 6, 2012 at 1:53 AM, Chris <plut...@gmail.com> wrote:
> 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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