This lesson started with an explanation for using the javax.imageio
package, to load images from an external image format into Java 2D™'s internal BufferedImage
format. Then it explains how to use the Graphics.drawImage()
to draw that image, with optional filtering.
The final stage is saving a BufferedImage
object into an external image format. This may be an image that was originally loaded by the Image I/O
class from an external image format and perhaps modified using the Java 2D APIs, or it may be one that was created by Java 2D.
The Image I/O
class provides a simple way to save images in a variety of image formats in the following example:
static boolean ImageIO.write(RenderedImage im, String formatName, File output) throws IOException
BufferedImage
class implements the RenderedImage
interface.
.
The formatName
parameter selects the image format in which to save the BufferedImage
.
try { BufferedImage bi = getMyImage(); // retrieve image File outputfile = new File("saved.png"); ImageIO.write(bi, "png", outputfile); } catch (IOException e) { ... }
The ImageIO.write
method calls the code that implements PNG writing a “PNG writer plug-in”. The term plug-in is used since Image I/O
is extensible and can support a wide range of formats.
But the following standard image format plugins : JPEG, PNG, GIF, BMP and WBMP are always be present.
Each image format has its advantages and disadvantages:
Format | Plus | Minus |
---|---|---|
GIF | Supports animation, and transparent pixels | Supports only 256 colors and no translucency |
PNG | Better alternative than GIF or JPG for high colour lossless images, supports translucency | Doesn't support animation |
JPG | Great for photographic images | Loss of compression, not good for text, screenshots, or any application where the original image must be preserved exactly |
For most applications it is sufficient to use one of these standard plugins. They have the advantage of being readily available. The Image I/O
class provides a way to plug in support for additional formats which can be used, and many such plug-ins exist. If you are interested in what file formats are available to load or save in your system, you may use the getReaderFormatNames
and getWriterFormatNames
methods of the ImageIO
class. These methods return an array of strings listing all of the formats supported in this JRE.
String writerNames[] = ImageIO.getWriterFormatNames();
The returned array of names will include any additional plug-ins that are installed and any of these names may be used as a format name to select an image writer. The following code example is a simple version of a complete image edit/touch up program which uses a revised version of the
ImageDrawingApplet.java
sample program which can be used as follows :
The complete code of this example is represented in
SaveImage.java
.
In this lesson you have learned just the basics of Image I/O
, which provides extensive support for writing images, including working directly with an ImageWriter
plug-in to achieve finer control over the encoding process. ImageIO can write multiple images, image metadata, and determine quality vs. size tradeoffs. For more information see
Java Image I/O API Guide.