[EntropyReduction]

If I change resolution of an image with gimp-image-set-resolution, that seems to have no effect on x/y/h/w arguments used in other gimp-* commands. E.g. if I increase resoklution form 72, 72 to 720, 720,

(gimp-rect-select image-id 0 0 720 720....)

Selects a rectangle 10" x 10", not 1" by 1".

Is there any way to persuade gimp to higher resolution units in commands like gimp-rect-select, gimp-pencil, etc?

Thanks for any help.

[RobA]

Changing the resolution doesn't change the pixel count! You have to scale the image to change the pixel count.

-Rob A>

[EntropyReduction]

Okay, need to be more specific about what I'm trying to do.

At simplest, say I want to draw a line 10mm long, drawing to be printed out on a printer capable of 600 dpi.

I want the line to be _exactly_ 10 mm, as close as possible at 600 dpi.

But gimp_pencil only knows about pixels, so I convert 72 pixel/inch (or whatever get_resolution tels me) / 25.4 to convert to pixels per mm
= 2.84. That makes 28.4 pixels for 10 mm. It's that .4 pixel that bothers me. If I round, floor, or ceiling, my line length is off by 10% or so.
Won't show on screen, but will matter on paper.

I tried making my drawing 10x required size and scaling down by factor of ten; I just end up with mush at line ends (interpolation at work, I suppose).

Any way round? Or just no way to be that accurate in GIMP?

Thanks

Alan

[saulgoode]

EntropyReduction said:

At simplest, say I want to draw a line 10mm long, drawing to be printed out on a printer capable of 600 dpi.

I want the line to be _exactly_ 10 mm, as close as possible at 600 dpi.

But gimp_pencil only knows about pixels, so I convert 72 pixel/inch (or whatever get_resolution tels me) / 25.4 to convert to pixels per mm = 2.84. That makes 28.4 pixels for 10 mm. It's that .4 pixel that bothers me. If I round, floor, or ceiling, my line length is off by 10% or so.

That should be 600 pixels/inch (your printer's resolution) divided by 25.4 == 23.6 pixels per mm. In other words, your script should draw a line 236 pixels long for the line to appear as 10 mm long on the printout (this results in an error of less than 0.22%).

[EntropyReduction]

saulgoode said:

EntropyReduction said:

At simplest, say I want to draw a line 10mm long, drawing to be printed out on a printer capable of 600 dpi.

I want the line to be _exactly_ 10 mm, as close as possible at 600 dpi.

But gimp_pencil only knows about pixels, so I convert 72 pixel/inch (or whatever get_resolution tels me) / 25.4 to convert to pixels per mm = 2.84. That makes 28.4 pixels for 10 mm. It's that .4 pixel that bothers me. If I round, floor, or ceiling, my line length is off by 10% or so.

That should be 600 pixels/inch (your printer's resolution) divided by 25.4 == 23.6 pixels per mm. In other words, your script should draw a line 236 pixels long for the line to appear as 10 mm long on the printout (this results in an error of less than 0.22%).

If I try to draw a line 236 pixels long, I get a line on screen 236 pixels long (236/72 or 3.27 inches). That prints out a line 3.27" long, no matter what printer resolution is (windows, gimp 2.6.7). Surely that's the way it's meant to work?

Ah, just looked at print dialog. So I could make a line 236 pixels long, then adjust resolution on print... dialog image settings to tell it to print 600 pixels/inch...?

Doesn't seem to be a way to cause printing to happen at a specified resolution using a gimp-* command?

Alan