[Scilab-users] {EXT} Fwd: plotting dots vs xfarc

[Antoine Monmayrant]

On 01/10/2020 09:05, Dang Ngoc Chan, Christophe wrote:
> Hello,
>
>> De la part de P M
>> Envoyé : mercredi 30 septembre 2020 16:50
>>
>> exact dot-coordinates, drawn as filled circles.
>> All pixel coordinates of such an area would have to have exactly one single pixel value.
>> The resulting graphic right now is stored via:      xs2bmp.
>> [...]
>> - It seems that the resulting pixels of the dot in the final image are not equally colored.
> I suspect the following thing: pixels are squares, not dots.
>
> So it may be that xs2bmp somehow inter-/extrapolate the colours.
> You then have a "leak" between the coloured pixel and its neighbours.
>
> You may try to draw squares of the exact size of the final pixel (e.g. 1/320 width and 1/200 height of the graphical window for a 320 × 200 raster picture).
>
> You may also try some functions from the image processing toolboxes.
Well, another approach would be to:
- use Matplot to display your image as a matrix, let's say [0:255] range.
- modify the data in the matrix to be displayed where you went to get 
your "dot": like your change your data to 256
- use a colormap that is grayscale from [0:255] and has a fancy color 
for 256 (blue?).

If you do this, you should get a perfect co-registration of your image 
and your "overlayed" markers.
Of course, your markers will not be circular dots, just a single pixel 
with what I described above, but you can also generate your own shapes 
(bigger squares, crosses, ~circles), provided that you use an odd number 
of pixels.

Hope it helps,

Antoine

>
> Hope this helps
>
> Regards
>
> --
> Christophe Dang Ngoc Chan
> cdang at wanadoo.fr
>
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