[Gimp-user] At 100%, my selection hasn't the size it should have

[rich404 <forums gimpusers com>]

> Hello,
>
> I have an image and I'd like to define the dimension of a selected
> area. I fisrt select the area that I want to resize. I then select the
> tool (Shift + T) and resize the selection. I noticed that after
> resizing, when I visualize the image with a 100% scale, the size of
> the image is not correct. I have not a little difference of one or two
> millimiters that could be due to the screen or whatever. But a big
> difference (30cm instead of 35cm in my case).
> Is it a normal display problem ? I mean, if I print it, will the
> dimensions be good ?

First and most important. Gimp is a raster editor and works in pixels. It can
show cms as units for your convenience, but it still works in pixels.

If you are not sure about the printing size. Check Image -> Image Properties and
that shows information: Size in Pixels / Print Size / and Resolution (ppi)

Another way is turn off View -> Dot-for-Dot  see:
https://docs.gimp.org/en/gimp-view-dot-for-dot.html

Providing the screen resolution is correctly set then, at 100% the image
displays as it is printed. See screenshot

> Second question :
> with this method of resizing, I only resize the selection. But what
> I'd like to do is to resize the hole image thanks to a reference
> within the image whose size is known. For example. if there is a rule
> on the image, I'd like to resize the whole image thanks to a size
> reference given by the rule.

Second Question. Not sure what you want.

A selection can be set to show centimetres in the tool options. Use the value
from that selection to enter into Image -> scale image. You might have to break
the link if the width / height proportions are different. See screenshot

rich: www.gimp-forum.net

Attachments:
* http://www.gimpusers.com/system/attachments/788/original/dot-for-dot.jpg
* http://www.gimpusers.com/system/attachments/789/original/thesame.jpg

-- 
rich404 (via www.gimpusers.com/forums)