com.trolltech.qt.gui
Class QImageWriter

java.lang.Object
  extended by com.trolltech.qt.internal.QSignalEmitterInternal
      extended by com.trolltech.qt.QSignalEmitter
          extended by com.trolltech.qt.QtJambiObject
              extended by com.trolltech.qt.gui.QImageWriter
All Implemented Interfaces:
QtJambiInterface

public class QImageWriter
extends QtJambiObject

The QImageWriter class provides a format independent interface for writing images to files or other devices. QImageWriter supports setting format specific options, such as the gamma level, compression level and quality, prior to storing the image. If you do not need such options, you can use QImage::save() or QPixmap::save() instead.

To store an image, you start by constructing a QImageWriter object. Pass either a file name or a device pointer, and the image format to QImageWriter's constructor. You can then set several options, such as the gamma level (by calling setGamma()) and quality (by calling setQuality()). canWrite() returns true if QImageWriter can write the image (i.e., the image format is supported and the device is open for writing). Call write() to write the image to the device.

If any error occurs when writing the image, write() will return false. You can then call error() to find the type of error that occurred, or errorString() to get a human readable description of what went wrong.

Call supportedImageFormats() for a list of formats that QImageWriter can write. QImageWriter supports all built-in image formats, in addition to any image format plugins that support writing.

See also:
QImageReader, QImageIOHandler, and QImageIOPlugin.


Nested Class Summary
static class QImageWriter.ImageWriterError
          This enum describes errors that can occur when writing images with QImageWriter.
 
Nested classes/interfaces inherited from class com.trolltech.qt.QSignalEmitter
QSignalEmitter.AbstractSignal, QSignalEmitter.PrivateSignal0, QSignalEmitter.PrivateSignal1, QSignalEmitter.PrivateSignal2, QSignalEmitter.PrivateSignal3, QSignalEmitter.PrivateSignal4, QSignalEmitter.PrivateSignal5, QSignalEmitter.PrivateSignal6, QSignalEmitter.PrivateSignal7, QSignalEmitter.PrivateSignal8, QSignalEmitter.PrivateSignal9, QSignalEmitter.Signal0, QSignalEmitter.Signal1, QSignalEmitter.Signal2, QSignalEmitter.Signal3, QSignalEmitter.Signal4, QSignalEmitter.Signal5, QSignalEmitter.Signal6, QSignalEmitter.Signal7, QSignalEmitter.Signal8, QSignalEmitter.Signal9
 
Nested classes/interfaces inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
com.trolltech.qt.internal.QSignalEmitterInternal.AbstractSignalInternal
 
Field Summary
 
Fields inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
currentSender
 
Constructor Summary
QImageWriter()
          Constructs an empty QImageWriter object.
QImageWriter(QIODevice device, QByteArray format)
          Constructs a QImageWriter object using the device device and image format format.
QImageWriter(java.lang.String fileName)
          Constructs a QImageWriter objects that will write to a file with the name fileName, using the image format format.
QImageWriter(java.lang.String fileName, QByteArray format)
          Constructs a QImageWriter objects that will write to a file with the name fileName, using the image format format.
 
Method Summary
 boolean canWrite()
          Returns true if QImageWriter can write the image; i.
 int compression()
          Returns the compression of the image.
 QIODevice device()
          Returns the device currently assigned to QImageWriter, or 0 if no device has been assigned.
 QImageWriter.ImageWriterError error()
          Returns the type of error that last occurred.
 java.lang.String errorString()
          Returns a human readable description of the last error that occurred.
 java.lang.String fileName()
          If the currently assigned device is a QFile, or if setFileName() has been called, this function returns the name of the file QImageWriter writes to.
 QByteArray format()
          Returns the format QImageWriter uses for writing images.
 float gamma()
          Returns the gamma level of the image.
 int quality()
          Returns the quality level of the image.
 void setCompression(int compression)
          This is an image format specific function that set the compression of an image.
 void setDevice(QIODevice device)
          Sets QImageWriter's device to device.
 void setFileName(java.lang.String fileName)
          Sets the file name of QImageWriter to fileName.
 void setFormat(QByteArray format)
          Sets the format QImageWriter will use when writing images, to format.
 void setGamma(float gamma)
          This is an image format specific function that sets the gamma level of the image to gamma.
 void setQuality(int quality)
          This is an image format specific function that sets the quality level of the image to quality.
 void setText(java.lang.String key, java.lang.String text)
          Sets the image text associated with the key key to text.
static java.util.List supportedImageFormats()
          Returns the list of image formats supported by QImageWriter.
 boolean supportsOption(QImageIOHandler.ImageOption option)
          Returns true if the writer supports option; otherwise returns false.
 boolean write(QImage image)
          Writes the image image to the assigned device or file name.
 
Methods inherited from class com.trolltech.qt.QtJambiObject
dispose, disposed, equals, finalize, reassignNativeResources, tr, tr, tr
 
Methods inherited from class com.trolltech.qt.QSignalEmitter
blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread
 
Methods inherited from class com.trolltech.qt.internal.QSignalEmitterInternal
__qt_signalInitialization
 
Methods inherited from class java.lang.Object
clone, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 
Methods inherited from interface com.trolltech.qt.QtJambiInterface
disableGarbageCollection, nativeId, nativePointer, reenableGarbageCollection, setJavaOwnership
 

Constructor Detail

QImageWriter

public QImageWriter()
Constructs an empty QImageWriter object. Before writing, you must call setFormat() to set an image format, then setDevice() or setFileName().


QImageWriter

public QImageWriter(QIODevice device,
                    QByteArray format)
Constructs a QImageWriter object using the device device and image format format.


QImageWriter

public QImageWriter(java.lang.String fileName)
Constructs a QImageWriter objects that will write to a file with the name fileName, using the image format format. If format is not provided, QImageWriter will detect the image format by inspecting the extension of fileName.


QImageWriter

public QImageWriter(java.lang.String fileName,
                    QByteArray format)
Constructs a QImageWriter objects that will write to a file with the name fileName, using the image format format. If format is not provided, QImageWriter will detect the image format by inspecting the extension of fileName.

Method Detail

canWrite

public final boolean canWrite()
Returns true if QImageWriter can write the image; i. ., the image format is supported and the assigned device is open for reading.

See also:
write(), setDevice(), and setFormat().


compression

public final int compression()
Returns the compression of the image.

See also:
setCompression().


device

public final QIODevice device()
Returns the device currently assigned to QImageWriter, or 0 if no device has been assigned.

See also:
setDevice().


error

public final QImageWriter.ImageWriterError error()
Returns the type of error that last occurred.

See also:
ImageWriterError , and errorString().


errorString

public final java.lang.String errorString()
Returns a human readable description of the last error that occurred.

See also:
error().


fileName

public final java.lang.String fileName()
If the currently assigned device is a QFile, or if setFileName() has been called, this function returns the name of the file QImageWriter writes to. Otherwise (i.e., if no device has been assigned or the device is not a QFile), an empty QString is returned.

See also:
setFileName(), and setDevice().


format

public final QByteArray format()
Returns the format QImageWriter uses for writing images.

See also:
setFormat().


gamma

public final float gamma()
Returns the gamma level of the image.

See also:
setGamma().


quality

public final int quality()
Returns the quality level of the image.

See also:
setQuality().


setCompression

public final void setCompression(int compression)
This is an image format specific function that set the compression of an image. For image formats that do not support setting the compression, this value is ignored.

The value range of compression depends on the image format. For example, the "tiff" format supports two values, 0(no compression) and 1(LZW-compression).

See also:
compression().


setDevice

public final void setDevice(QIODevice device)
Sets QImageWriter's device to device. If a device has already been set, the old device is removed from QImageWriter and is otherwise left unchanged.

If the device is not already open, QImageWriter will attempt to open the device in QIODevice::WriteOnly mode by calling open(). Note that this does not work for certain devices, such as QProcess, QTcpSocket and QUdpSocket, where more logic is required to open the device.

See also:
device(), and setFileName().


setFileName

public final void setFileName(java.lang.String fileName)
Sets the file name of QImageWriter to fileName. Internally, QImageWriter will create a QFile and open it in QIODevice::WriteOnly mode, and use this file when writing images.

See also:
fileName(), and setDevice().


setFormat

public final void setFormat(QByteArray format)
Sets the format QImageWriter will use when writing images, to format. format is a case insensitive text string. Example:
        QImageWriter writer = new QImageWriter();
        writer.setFormat(new QByteArray("png")); // same as writer.setFormat("PNG");
You can call supportedImageFormats() for the full list of formats QImageWriter supports.

See also:
format().


setGamma

public final void setGamma(float gamma)
This is an image format specific function that sets the gamma level of the image to gamma. For image formats that do not support setting the gamma level, this value is ignored.

The value range of gamma depends on the image format. For example, the "png" format supports a gamma range from 0.0 to 1.0.

See also:
gamma(), and quality().


setQuality

public final void setQuality(int quality)
This is an image format specific function that sets the quality level of the image to quality. For image formats that do not support setting the quality, this value is ignored.

The value range of quality depends on the image format. For example, the "jpeg" format supports a quality range from 0 (low quality, high compression) to 100 (high quality, low compression).

See also:
quality().


setText

public final void setText(java.lang.String key,
                          java.lang.String text)
Sets the image text associated with the key key to text. This is useful for storing copyright information or other information about the image. Example:
        QImage image = new QImage("some/image.jpeg");
        QImageWriter writer = new QImageWriter("images/outimage.png", new QByteArray("png"));
        writer.setText("Author", "John Smith");
        writer.write(image);
If you want to store a single block of data (e.g., a comment), you can pass an empty key, or use a generic key like "Description".

The key and text will be embedded into the image data after calling write().

Support for this option is implemented through QImageIOHandler::Description .

See also:
QImage::setText(), and QImageReader::text().


supportsOption

public final boolean supportsOption(QImageIOHandler.ImageOption option)
Returns true if the writer supports option; otherwise returns false.

Different image formats support different options. Call this function to determine whether a certain option is supported by the current format. For example, the PNG format allows you to embed text into the image's metadata (see text()).

        QImageWriter writer = new QImageWriter(fileName);
        if (writer.supportsOption(QImageIOHandler.ImageOption.Description))
            writer.setText("Author", "John Smith");
Options can be tested after the writer has been associated with a format.

See also:
QImageReader::supportsOption(), and setFormat().


write

public final boolean write(QImage image)
Writes the image image to the assigned device or file name. Returns true on success; otherwise returns false. If the operation fails, you can call error() to find the type of error that occurred, or errorString() to get a human readable description of the error.

See also:
canWrite(), error(), and errorString().


supportedImageFormats

public static java.util.List supportedImageFormats()
Returns the list of image formats supported by QImageWriter.

By default, Qt can write the following formats:

Format
Description
BMP Windows Bitmap
JPG Joint Photographic Experts Group
JPEG Joint Photographic Experts Group
PNG Portable Network Graphics
PPM Portable Pixmap
TIFF Tagged Image File Format
XBM X11 Bitmap
XPM X11 Pixmap
Reading and writing SVG files is supported through Qt's SVG Module.

See also:
setFormat(), QImageReader::supportedImageFormats(), and QImageIOPlugin.