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<title>6.5. Scale Image</title>
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<th colspan="3" align="center" id="chaptername">6.5. Scale Image</th>
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<div class="sect2" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h3 class="title"><a id="gimp-image-scale"></a>6.5. Scale Image</h3>
</div>
</div>
</div>
<a id="id3351671" class="indexterm"></a>
<div class="mediaobject">
<img src="../images/dialogs/dialogs-image-scale-image.png" />
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<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3352324"></a>Overview</h4>
</div>
</div>
</div>
<p>
The Scale Image function enlarges or reduces the image. It
changes the scale of the image content and resizes the canvas
so that the whole image remains visible.
It also gives you informations about the size and the resolution
your image will have when printed.
</p>
<p>
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. If this happens you
will be warned before the operation is applied.
</p>
<p>
If you want to scale a particular layer, use the function Scale
Layer
</p>
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<div class="simplesect" lang="en" xml:lang="en">
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<div>
<div>
<h4 class="title"><a id="id3352354"></a>Pixel Dimensions</h4>
</div>
</div>
</div>
<p>
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.
</p>
<p>
This section deals with making your image bigger or smaller,
what dimensions will be in RAM and then in file after saving.
</p>
<p>
When you open the dialog, the displayed dimensions are that of
the original image. On screen, all pixels are displayed and the
dimensions depend on the screen resolution and on the
<a href="ch05s05s02.html" title="5.2. Dot for Dot">Dot dor Dot</a> option
you have choosen.
</p>
<p>
You can set there the <span class="emphasis"><em>Width</em></span> and the
<span class="emphasis"><em>Height</em></span> you want to give to your image by
adding or removing pixels, resulting in a variation of
dimensions.
Click on arrowheads to change the value in the text box. If you
have clicked in this box, you can use the Up and Down arrow keys
for precise setting.
You can act directly on linear dimensions in the unit you want,
and that will add or remove pixels. These linear
dimensions in memory are not much useful: they depend on
resolution and are different from that on screen. Only pixels
are important, from which the section name.
</p>
<p>
<span class="emphasis"><em>Ratio</em></span> is the ratio between the original
dimension and the new dimension, for each X and Y axis. Default
is 1. You can change it. If the adjacent Chain is intact both
axis will develop jointly. If you break it by clicking on it,
then you can set every axis separately: this will result in
deforming the image.
</p>
<p>
You can enlarge an image safely only if the original has a high
resolution, pixels enough to avoid adding new pixels. Else,
missing pixels are calculated by interpolation but no new detail
is added and the more enlarged the more blurred, with aliasing.
You can improve the result by using the filter
<a href="ch06s06s06.html" title="6.6. Sharpen">Sharpen</a> (after scaling)
but the best method is to use a high resolution when scanning an
image you plan to enlarge.
</p>
<p>
Reducing your image may be necessary if you intend it to a Web
page. You have to take in account that Internet users still have
15' screens and that your big image cann't be completely
displayed on them. Most of screens work in 800x600 and 1024x768
resolution.
</p>
<p>
Adding or removing pixels is called "Resampling".
</p>
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3352356"></a>Print Size & Display Unit</h4>
</div>
</div>
</div>
<p>
This section deals with the size and resolution your image will
have when printed. Remember that all the pixels of the image
will be printed and that there will be no splitting.
</p>
<p>
When you launch the Scale function GIMP displays the dimensions
of the original image that will allow printing without
deformation.
</p>
<p>
As for screen, you can enlarge or reduce the printed image with
the same risks.
</p>
<p>
Resolution deals with ouput resolution, that is the number of
pixels that will be used in every inch of the printed image. You
must not mistake the output resolution with the printer
resolution which is expressed in dpi (dot per inch): several
dots are necessary to print a pixel.
</p>
<p>
The resolution proposed by GIMP is the resolution of the
original image. If you increase the output resolution the
printed image will be smaller since more pixels are used for an
inch. Conversely and for the same reason resizing modifies
resolution.
</p>
<p>
Increasing resolution results in increasing the printed image
sharpness. This is quite different from simply reducing the
image size since no pixels are removed.
</p>
<p>
Modifying resolution also acts for the image file. It is not
visible at the pixel level but it is at the dimension level
(inch for example). By reducing resolution you decrease the
dimensions in the image file. By combining resolution reduction
and pixel reduction and by restablishing the original dimensions
of your image you can reduce the weight of your image file if
PNG compression is not enough.
</p>
</div>
<div class="simplesect" lang="en" xml:lang="en">
<div class="titlepage">
<div>
<div>
<h4 class="title"><a id="id3352481"></a>Interpolation Type</h4>
</div>
</div>
</div>
<p>
Here you can select the method used to interpolate the color of
added pixels, valid for screen display and printing.
</p>
<div class="itemizedlist">
<ul type="disc">
<li>
<p>
<span class="emphasis"><em>None</em></span>: no interpolation is used. Pixels
are simply enlarged as they are when zooming.
</p>
</li>
<li>
<p>
<span class="emphasis"><em>Linear</em></span>:
</p>
</li>
<li>
<p>
<span class="emphasis"><em>Cubic</em></span>: The best method but needing much
calculation.
</p>
</li>
</ul>
</div>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Note]" src="../images/note.png" />
</td>
<th align="left">Note</th>
</tr>
<tr>
<td colspan="2" align="left" valign="top">
<p>
To prepare your image for printing in a particular format use the
<a href="ch03s04s02.html" title="4.2. Crop Tool">Crop</a> tool, with inch for unit:
The displayed size is the printing size.
</p>
</td>
</tr>
</table>
</div>
<a id="gimp-image-scale-warning"></a>
<div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Note]" src="../images/note.png" />
</td>
<th align="left">Note</th>
</tr>
<tr>
<td colspan="2" align="left" valign="top">
<p>
If scaling would produce an image larger than the "Maximum new
image size" set in the <a href="ch04s18s14.html" title="18.14. Environment">Environment</a> 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.
</p>
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