Resizes grayscale and truecolor images using filters.
For other image types (including paletted or bilevel images), you might
want to use the
ScaleReplication
class or convert the images to
grayscale (or RGB truecolor) first and then use this class.
Several algorithms for resampling are implemented, they differ in resulting image quality
and computational complexity.
Usage example
This will scale
image
to 150 percent of its original size
in both directions, using the Lanczos3 filter type:
Resample resample = new Resample();
resample.setInputImage(image);
resample.setSize(image.getWidth() * 3 / 2, image.getHeight() * 3 / 2);
resample.setFilter(Resample.FILTER_TYPE_LANCZOS3);
resample.process();
PixelImage scaledImage = resample.getOutputImage();
Known problems
- Scaling down certain images (with stripe or checkers patterns in them) will
lead to moire effects in the resulting image.
These effects can be somewhat reduced by scaling down in several step (e.g.
first from 1600 x 1200 to 800 x 600, then from 800 x 600 to 400 x 300, and so on).
- Scaling down with filter type
FILTER_TYPE_BOX
can lead to errors in the scaled image.
No fix known yet. Workaround: Use the class ScaleReplication
.
Origin
This code is a port of Anders Melander's
Object Pascal (Delphi) unit
resample.pas to Java.
The Delphi code is an adaptation (with some improvements) of
Dale Schumacher's
fzoom C code.
Check out the homepage for the Delphi resample code, a demo application
to compare the different filtering algorithms is also provided:
http://www.melander.dk/delphi/resampler/index.html.
You will also find the original C code there.
The site seems to have gone for good.
Theory
The theoretical background for all implementations is Dale Schumacher's article
General Filtered Image Rescaling
in
Graphics Gems III, editor David Kirk, Academic Press, pages 8-16, 1994.
The
Graphics Gems Repository can be found at
http://www.acm.org/tog/GraphicsGems/.
It also includes information on the books and how to order them.
FILTER_TYPE_BELL
public static final int FILTER_TYPE_BELL
Constant for the Bell filter.
FILTER_TYPE_BOX
public static final int FILTER_TYPE_BOX
Constant for the Box filter (also known as Nearest Neighbor filter).
FILTER_TYPE_B_SPLINE
public static final int FILTER_TYPE_B_SPLINE
Constant for the B-Spline filter.
FILTER_TYPE_HERMITE
public static final int FILTER_TYPE_HERMITE
Constant for the Hermite filter.
FILTER_TYPE_LANCZOS3
public static final int FILTER_TYPE_LANCZOS3
Constant for the Lanczos3 filter.
FILTER_TYPE_MITCHELL
public static final int FILTER_TYPE_MITCHELL
Constant for the Mitchell filter.
FILTER_TYPE_TRIANGLE
public static final int FILTER_TYPE_TRIANGLE
Constant for the Triangle filter (also known as Linear filter or Bilinear filter).
outHeight
private Integer outHeight
outWidth
private Integer outWidth
createFilter
private static ResampleFilter createFilter(int filterType)
getFilter
public ResampleFilter getFilter()
Returns the filter to be used in this operation.
- ResampleFilter object or
null
if none was defined yet
getFilterNames
public static String[] getFilterNames()
Returns the names of all predefined filters.
Each FILTER_TYPE_xyz constant can be used as an index into the array that is returned.
Names are retrieved by creating an object of each predefined filter class and calling its
getName method.
- String array with filter names
getNumFilters
public static int getNumFilters()
Returns the number of predefined filters.
setFilter
public void setFilter(int filterType)
Sets a new filter type, using the default sampling radius of that filter.
filterType
- the new filter type, one of the FILTER_TYPE_xyz constants of this class
setFilter
public void setFilter(int filterType,
float samplingRadius)
Sets a new filter type with a user-defined sampling radius.
filterType
- the new filter type, one of the FILTER_TYPE_xyz constants of this classsamplingRadius
- the sampling radius to be used with that filter, must be larger than 0.0f
setFilter
public void setFilter(ResampleFilter newFilter)
Set a new filter object to be used with this operation.
newFilter
- a resample filter to be used for scaling
setSize
public void setSize(int width,
int height)
Set the pixel resolution of the output image.
width
- the horizontal resolution of the output imageheight
- the vertical resolution of the output image