com.trolltech.qt.gui
Class QImageWriter

java.lang.Object
  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, 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.Signal0, QSignalEmitter.Signal1<A>, QSignalEmitter.Signal2<A,B>, QSignalEmitter.Signal3<A,B,C>, QSignalEmitter.Signal4<A,B,C,D>, QSignalEmitter.Signal5<A,B,C,D,E>, QSignalEmitter.Signal6<A,B,C,D,E,F>, QSignalEmitter.Signal7<A,B,C,D,E,F,G>, QSignalEmitter.Signal8<A,B,C,D,E,F,G,H>, QSignalEmitter.Signal9<A,B,C,D,E,F,G,H,I>
 
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)
          Equivalent to QImageWriter(fileName, QByteArray()).
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.e., the image format is supported and the assigned device is open for reading.
 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.
static QImageWriter fromNativePointer(QNativePointer nativePointer)
          This function returns the QImageWriter instance pointed to by nativePointer
 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<QByteArray> 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, finalize, reassignNativeResources, tr, tr, tr
 
Methods inherited from class com.trolltech.qt.QSignalEmitter
blockSignals, disconnect, disconnect, signalsBlocked, signalSender, thread
 
Methods inherited from class java.lang.Object
clone, equals, 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)

Equivalent to QImageWriter(fileName, QByteArray()).


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.e., the image format is supported and the assigned device is open for reading.

See Also:
write, setDevice, 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, 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, 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, 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, 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;
    writer.setFormat("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, 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("some/image.jpeg");
    QImageWriter writer("images/outimage.png", "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, 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(fileName);
    if (writer.supportsOption(QImageIOHandler::Description))
        writer.setText("Author", "John Smith");

Options can be tested after the writer has been associated with a format.

See Also:
QImageReader::supportsOption, 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, errorString

supportedImageFormats

public static java.util.List<QByteArray> supportedImageFormats()

Returns the list of image formats supported by QImageWriter.

By default, Qt can write the following formats:

FormatDescription
BMPWindows Bitmap
JPGJoint Photographic Experts Group
JPEGJoint Photographic Experts Group
PNGPortable Network Graphics
PPMPortable Pixmap
TIFFTagged Image File Format
XBMX11 Bitmap
XPMX11 Pixmap

See Also:
setFormat, QImageReader::supportedImageFormats, QImageIOPlugin

fromNativePointer

public static QImageWriter fromNativePointer(QNativePointer nativePointer)
This function returns the QImageWriter instance pointed to by nativePointer

Parameters:
nativePointer - the QNativePointer of which object should be returned.