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### 6.7. Scale Image

#### Overview

The Scale Image function enlarges or reduces the image by changing the number of pixels it contains. It changes the size of the image content and resizes the canvas accordingly.

It acts on the whole image. If your image has layers with different sizes, it is possible that making the image smaller will shrink some of them completely away (a layer cannot be less than 1 pixel wide or high). If this happens you will be warned before the operation is applied.

If you want to scale a particular layer only, use the function Scale Layer.

#### Image Size

You must remember that an image can be located in four places: In the image file, in the RAM after loading, on your screen when displayed, on paper after printing. Scaling the image changes the number of pixels (information) the image contains, so it directly changes the amount of memory the image needs (in RAM or in a file).

However print size depends also on the resolution of the image (which basically says, how many pixels each inch on paper contains). If you want to change printing size without scaling the image and changing the number of pixels it consist of, you should use the Print Size dialog. Screen size also depends not only on pixel number, but also on the screen resolution, zoom factor and the Dot dor Dot option.

When you launch the Scale function GIMP 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 adjacent Chain icon is intact, width and height keep their proportion. If you break it by clicking on it, you can set them separately: this will result in deforming the image.

However you do not have to set dimensions in pixels, you can choose different units from the dropdown menu. If you choose percent as units, you can set the image size relatively to its original size. You can also use physical units like inches or millimeters. However if you do that, you should keep attention to the X/Y resolution fields (and set them to an appropriate value), because image dimensions in pixels, which are being changed by this dialog, are computed from physical units using these resolution values.

If you are enlarging an image beyond its original size, missing pixels are calculated by interpolation but no new detail is added. The more enlarged the image is, the more blurred it becomes. The exact result of enlarging depends on the chosen interpolation method. You can improve the result by using the filter Sharpen (after scaling) but the best method is to use a high resolution when scanning, taking digital photographs aor producing digital images by other means. Not scaling up well is an inherit nature of raster images.

Reducing your image may be necessary if you intend it to a Web page. You have to take in account that most Internet users have relatively small screens and that your big image cann't be completely displayed on them. Many of screens work in 1024x768 or even smaller resolution.

Adding or removing pixels is called "Resampling".

#### Interpolation Type

The Interpolation dropdown list provides a selection of available methods of interpolating the color of pixels in a scaled image:

- None: 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 relativelly fast, but still provides fairly good results.

- Cubic: The best, highest quality but also the slowest method available.

| Note

If scaling would produce an image larger than the "Maximum new image size" set in the Environment page of the Preferences dialog, you are warned and asked to confirm that you really want to do it. Saying yes will not necessarily have bad consequences, but you should give it a moment of thought, because very large images consume a lot of resources, and outrageously large images may consume more resources than you have, causing GIMP to crash or otherwise behave unpleasantly.

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