gnuplot-beta

image or rgbimage plots with zero decorations

[Dima K. <gn...@di...>]

Hi. I'm pretty sure this isn't possible, but I'd like to ask anyway.

I have a gnuplot script to plot an image, with some extra stuff on top
of it. Something like this:

  set terminal png
  set output "out.png"
  plot "image.png" binary filetype=png flipy with rgbimage, "data" with lines

Ideally I would like the result to be a .png file with the same
dimensions as "image.png", and I would like "image.png" to fill the
whole output plot. I.e. I want to annotate "image.png", but not scale it
in any way.

There are some options that help somewhat, but don't do everything:

  set autoscale noextend
  set size ratio -1

In practice, what I end up doing is to manually find the pixel size for
the "set terminal png" command that results in the output image of the
correct size, and then I crop "out.png". Is there a better way?

Thanks.

Re: image or rgbimage plots with zero decorations

[Ethan A M. <me...@uw...>]

On Friday, 4 April 2025 10:32:41 PDT Dima Kogan wrote:
> Hi. I'm pretty sure this isn't possible, but I'd like to ask anyway.
> 
> I have a gnuplot script to plot an image, with some extra stuff on top
> of it. Something like this:
> 
>   set terminal png
>   set output "out.png"
>   plot "image.png" binary filetype=png flipy with rgbimage, "data" with lines
> 
> Ideally I would like the result to be a .png file with the same
> dimensions as "image.png", and I would like "image.png" to fill the
> whole output plot. I.e. I want to annotate "image.png", but not scale it
> in any way.
> 
> There are some options that help somewhat, but don't do everything:
> 
>   set autoscale noextend
>   set size ratio -1

I would have thought the heart of it would be
    set autoscale noextend 
    set margins 0,0,0,0

I think using "set size ratio" is counter-productive for this purpose.

	Ethan
 
> In practice, what I end up doing is to manually find the pixel size for
> the "set terminal png" command that results in the output image of the
> correct size, and then I crop "out.png". Is there a better way?
> 
> Thanks.

Re: image or rgbimage plots with zero decorations

[Dima K. <gn...@di...>]

Ethan A Merritt <me...@uw...> writes:

> I would have thought the heart of it would be
>     set autoscale noextend 
>     set margins 0,0,0,0

Oh wow. That actually does 99% of what I want. Thank you!

The extra 1% is probably a bug: I have this script:

  set margin 0,0,0,0
  unset xtics
  unset ytics
  set terminal png size 1027,1035
  set output "/tmp/tst.png"

  plot "/tmp/input.png" binary filetype=png with rgbimage notitle

where the requested png size is the dimensions of /tmp/input.png. If I
look at the input and output side by side, I see the image shift by 1
pixel in each direction.

Thanks for the suggestion.