The Scale Image command enlarges or reduces
the physical size of the image by changing the number of pixels it
contains. It changes the size of the contents of the image and resizes
the canvas accordingly.
It operates on the entire image. If your image has layers of different
sizes, making the image smaller could shrink some of them down to
nothing, since a layer cannot be less than one pixel wide or high. If
this happens, you will be warned before the operation is performed.
If you only want to scale a particular layer, use the
Scale Layer command.
If scaling would produce an image larger than the
“Maximum new image size” set in the
Environment page of the
Preferences dialog (which has a default of 64Mb), you are warned and
asked to confirm the operation before it is performed. You may not
experience any problems if you confirm the operation, but you should
be aware that very large images consume a lot of resources and
extremely large images may take more resources than you have,
causing GIMP to crash or not perform well.
Activating the Command
You can access this command from the image menubar through
The “Scale Image” Dialog
You should keep in mind that an image can be located in one of
four places: in the image file, in RAM after it has been loaded,
on your screen when it is displayed, or on paper after it has been
printed. Scaling the image changes the number of pixels (the
amount of information) the image contains, so it directly affects
the amount of memory the image needs (in RAM or in a file).
However printing size also depends upon the resolution of the
image, which essentially determines how many pixels there will
be on each inch of paper. If you want to change the printing
size without scaling the image and changing the number of pixels
in it, you should use the
Print Size dialog.
The screen size depends not only on the number of pixels, but
also on the screen resolution, the zoom factor and the setting
of the Dot for Dot
When you click on the Scale
command, the dialog displays the dimensions of the
original image in pixels. You can set the
Width and the
Height you want to give to your
image by adding or removing pixels. If the chain icon next
to the Width and Height boxes is unbroken, the Width and
Height will stay in the same proportion to each other. If
you break the chain by clicking on it, you can set them
independently, but this will distort the image.
However, you do not have to set the dimensions in pixels.
You can choose different units from the drop-down menu.
If you choose percent as the units, you can set the image
size relative to its original size. You can also use
physical units, such as inches or millimeters. If you do
that, you should set the X resolution
and Y resolution fields to
appropriate values, because they are used to convert
between physical units and image dimensions in pixels.
If you enlarge an image beyond its original size,
GIMP calculates the missing
pixels by interpolation, but it does not add any new
detail. The more you enlarge an image, the more blurred
it becomes. The appearance of an enlarged image depends
upon the interpolation method you choose. You may improve
the appearance by using the
after you have scaled an image, but it is best to
use high resolution when you scan, take digital
photographs or produce digital images by other means.
Raster images inherently do not scale up well.
You may need to reduce your image if you intend to use it on
a web page. You have to consider that most internet users
have relatively small screens which cannot completely
display a large image. Many screens have a resolution of
1024x768 or even less.
Adding or removing pixels is called
X resolution; Y resolution
You can set the printing resolution for the image in the
and Y resolution
fields. You can also change the units of measurement by
using the drop-down menu.
To change the image size, either some pixels have to be removed
or new pixels must be added. The process you use determines the
quality of the result. The Interpolation
drop down list provides a selection of available methods of
interpolating the color of pixels in a scaled image:
No interpolation is used. Pixels are simply enlarged
or removed, as they are when zooming. This method is low
quality, but very fast.
Linear: This method is relatively
fast, but still provides fairly good results.
The method that produces the best results, but also
the slowest method.
See also the Scale tool,
which lets you scale a layer, a selection or a path.