QtGui.QImageReader Class Reference

The QImageReader class provides a format independent interface for reading images from files or other devices. More...

Inheritance diagram for QtGui.QImageReader:

Collaboration diagram for QtGui.QImageReader:

Public Types
enum	ImageReaderError {   DeviceError = 2, FileNotFoundError = 1, InvalidDataError = 4, UnknownError = 0,   UnsupportedFormatError = 3 }
	More...

Public Member Functions
	QImageReader ()
	QImageReader (QIODevice device)
	QImageReader (QIODevice device, QByteArray format)
	QImageReader (string fileName)
	QImageReader (string fileName, QByteArray format)
virtual void	CreateProxy ()
new bool	CanRead ()
new int	CurrentImageNumber ()
new QRect	CurrentImageRect ()
new QImageReader.ImageReaderError	Error ()
new string	ErrorString ()
new int	ImageCount ()
new QImage.Format	ImageFormat ()
new bool	JumpToImage (int imageNumber)
new bool	JumpToNextImage ()
new int	LoopCount ()
new int	NextImageDelay ()
new QImage	Read ()
new bool	Read (QImage image)
new QSize	Size ()
new bool	SupportsAnimation ()
new bool	SupportsOption (QImageIOHandler.ImageOption option)
new string	Text (string key)
new System.Collections.Generic.List < string >	TextKeys ()
new void	Dispose ()

Static Public Member Functions
static QByteArray	ImageFormat (QIODevice device)
static QByteArray	ImageFormat (string fileName)
static System.Collections.Generic.List < QByteArray >	SupportedImageFormats ()

Protected Member Functions
	QImageReader (System.Type dummy)

Protected Attributes
SmokeInvocation	interceptor

Properties
new bool	AutoDetectImageFormat [get, set]
new QColor	BackgroundColor [get, set]
new QRect	ClipRect [get, set]
new bool	DecideFormatFromContent [get, set]
new QIODevice	Device [get, set]
new string	FileName [get, set]
new QByteArray	Format [get, set]
new int	Quality [get, set]
new QRect	ScaledClipRect [get, set]
new QSize	ScaledSize [get, set]
virtual System.IntPtr	SmokeObject [get, set]

Detailed Description

The QImageReader class provides a format independent interface for reading images from files or other devices.

The most common way to read images is through QImage and QPixmap's constructors, or by calling QImage::load() and QPixmap::load(). QImageReader is a specialized class which gives you more control when reading images. For example, you can read an image into a specific size by calling setScaledSize(), and you can select a clip rect, effectively loading only parts of an image, by calling setClipRect(). Depending on the underlying support in the image format, this can save memory and speed up loading of images.

To read an image, you start by constructing a QImageReader object. Pass either a file name or a device pointer, and the image format to QImageReader's constructor. You can then set several options, such as the clip rect (by calling setClipRect()) and scaled size (by calling setScaledSize()). canRead() returns the image if the QImageReader can read the image (i.e., the image format is supported and the device is open for reading). Call read() to read the image.

If any error occurs when reading the image, read() will return a null QImage. 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 QImageReader can read. QImageReader supports all built-in image formats, in addition to any image format plugins that support reading.

QImageReader autodetects the image format by default, by looking at the provided (optional) format string, the file name suffix, and the data stream contents. You can enable or disable this feature, by calling setAutoDetectImageFormat().

See also QImageWriter, QImageIOHandler, and QImageIOPlugin.

Member Enumeration Documentation

enum QtGui.QImageReader.ImageReaderError

This enum describes the different types of errors that can occur when reading images with QImageReader.

Enumerator:

DeviceError	QImageReader encountered a device error when reading the image. You can consult your particular device for more details on what went wrong.
FileNotFoundError	QImageReader was used with a file name, but not file was found with that name. This can also happen if the file name contained no extension, and the file with the correct extension is not supported by Qt.
InvalidDataError	The image data was invalid, and QImageReader was unable to read an image from it. The can happen if the image file is damaged.
UnknownError	An unknown error occurred. If you get this value after calling read(), it is most likely caused by a bug in QImageReader.
UnsupportedFormatError	Qt does not support the requested image format.

Constructor & Destructor Documentation

QtGui.QImageReader.QImageReader ( System.Type  dummy )

protected

QtGui.QImageReader.QImageReader

(

)

Constructs an empty QImageReader object. Before reading an image, call setDevice() or setFileName().

QtGui.QImageReader.QImageReader

(

QIODevice

device

)

Constructs an empty QImageReader object. Before reading an image, call setDevice() or setFileName().

QtGui.QImageReader.QImageReader	(	QIODevice	device,
		QByteArray	format
	)

Constructs an empty QImageReader object. Before reading an image, call setDevice() or setFileName().

QtGui.QImageReader.QImageReader

(

string

fileName

)

Constructs an empty QImageReader object. Before reading an image, call setDevice() or setFileName().

QtGui.QImageReader.QImageReader	(	string	fileName,
		QByteArray	format
	)

Constructs an empty QImageReader object. Before reading an image, call setDevice() or setFileName().

Member Function Documentation

new bool QtGui.QImageReader.CanRead

(

)

Returns true if an image can be read for the device (i.e., the image format is supported, and the device seems to contain valid data); otherwise returns false.

canRead() is a lightweight function that only does a quick test to see if the image data is valid. read() may still return false after canRead() returns true, if the image data is corrupt.

For images that support animation, canRead() returns false when all frames have been read.

See also read() and supportedImageFormats().

virtual void QtGui.QImageReader.CreateProxy ( )

virtual

new int QtGui.QImageReader.CurrentImageNumber

(

)

For image formats that support animation, this function returns the sequence number of the current frame. If the image format doesn't support animation, 0 is returned.

This function returns -1 if an error occurred.

See also supportsAnimation(), QImageIOHandler::currentImageNumber(), and canRead().

new QRect QtGui.QImageReader.CurrentImageRect

(

)

For image formats that support animation, this function returns the rect for the current frame. Otherwise, a null rect is returned.

See also supportsAnimation() and QImageIOHandler::currentImageRect().

new void QtGui.QImageReader.Dispose

(

)

new QImageReader.ImageReaderError QtGui.QImageReader.Error

(

)

Returns the type of error that occurred last.

See also ImageReaderError and errorString().

new string QtGui.QImageReader.ErrorString

(

)

Returns a human readable description of the last error that occurred.

See also error().

new int QtGui.QImageReader.ImageCount

(

)

For image formats that support animation, this function returns the total number of images in the animation. If the format does not support animation, 0 is returned.

This function returns -1 if an error occurred.

See also supportsAnimation(), QImageIOHandler::imageCount(), and canRead().

new QImage.Format QtGui.QImageReader.ImageFormat

(

)

Returns the format of the image, without actually reading the image contents. The format describes the image format QImageReader::read() returns, not the format of the actual image.

If the image format does not support this feature, this function returns an invalid format.

This function was introduced in Qt 4.5.

See also QImageIOHandler::ImageOption, QImageIOHandler::option(), and QImageIOHandler::supportsOption().

static QByteArray QtGui.QImageReader.ImageFormat ( QIODevice  device )

static

If supported, this function returns the image format of the device device. Otherwise, an empty string is returned.

See also QImageReader::autoDetectImageFormat().

static QByteArray QtGui.QImageReader.ImageFormat ( string  fileName )

static

If supported, this function returns the image format of the file fileName. Otherwise, an empty string is returned.

new bool QtGui.QImageReader.JumpToImage

(

int

imageNumber

)

For image formats that support animation, this function skips to the image whose sequence number is imageNumber, returning true if successful or false if the corresponding image cannot be found.

The next call to read() will attempt to read this image.

See also jumpToNextImage() and QImageIOHandler::jumpToImage().

new bool QtGui.QImageReader.JumpToNextImage

(

)

For image formats that support animation, this function steps over the current image, returning true if successful or false if there is no following image in the animation.

The default implementation calls read(), then discards the resulting image, but the image handler may have a more efficient way of implementing this operation.

See also jumpToImage() and QImageIOHandler::jumpToNextImage().

new int QtGui.QImageReader.LoopCount

(

)

For image formats that support animation, this function returns the number of times the animation should loop. If this function returns -1, it can either mean the animation should loop forever, or that an error occurred. If an error occurred, canRead() will return false.

See also supportsAnimation(), QImageIOHandler::loopCount(), and canRead().

new int QtGui.QImageReader.NextImageDelay

(

)

For image formats that support animation, this function returns the number of milliseconds to wait until displaying the next frame in the animation. If the image format doesn't support animation, 0 is returned.

This function returns -1 if an error occurred.

See also supportsAnimation(), QImageIOHandler::nextImageDelay(), and canRead().

new QImage QtGui.QImageReader.Read

(

)

Reads an image from the device. On success, the image that was read is returned; otherwise, a null QImage is returned. You can then call error() to find the type of error that occurred, or errorString() to get a human readable description of the error.

For image formats that support animation, calling read() repeatedly will return the next frame. When all frames have been read, a null image will be returned.

See also canRead(), supportedImageFormats(), supportsAnimation(), and QMovie.

new bool QtGui.QImageReader.Read

(

QImage

image

)

This is an overloaded function.

Reads an image from the device into image, which must point to a QImage. Returns true on success; otherwise, returns false.

If image has same format and size as the image data that is about to be read, this function may not need to allocate a new image before reading. Because of this, it can be faster than the other read() overload, which always constructs a new image; especially when reading several images with the same format and size.

QImage icon(64, 64, QImage::Format_RGB32);

QImageReader reader("icon_64x64.bmp");

if (reader.read(&icon)) {

// Display icon

}

For image formats that support animation, calling read() repeatedly will return the next frame. When all frames have been read, a null image will be returned.

See also canRead(), supportedImageFormats(), supportsAnimation(), and QMovie.

new QSize QtGui.QImageReader.Size

(

)

Returns the size of the image, without actually reading the image contents.

If the image format does not support this feature, this function returns an invalid size. Qt's built-in image handlers all support this feature, but custom image format plugins are not required to do so.

See also QImageIOHandler::ImageOption, QImageIOHandler::option(), and QImageIOHandler::supportsOption().

static System.Collections.Generic.List<QByteArray> QtGui.QImageReader.SupportedImageFormats ( )

static

Returns the list of image formats supported by QImageReader.

By default, Qt can read the following formats:

FormatDescription

BMP Windows Bitmap

GIF Graphic Interchange Format (optional)

JPG Joint Photographic Experts Group

JPEG Joint Photographic Experts Group

MNG Multiple-image Network Graphics

PNG Portable Network Graphics

PBM Portable Bitmap

PGM Portable Graymap

PPM Portable Pixmap

TIFF Tagged Image File Format

XBM X11 Bitmap

XPM X11 Pixmap

SVG Scalable Vector Graphics

TGA Targa Image Format

Reading and writing SVG files is supported through Qt's SVG Module.

TGA support only extends to reading non-RLE compressed files. In particular calls to capabilities for the tga plugin returns only QImageIOPlugin::CanRead, not QImageIOPlugin::CanWrite.

To configure Qt with GIF support, pass -qt-gif to the configure script or check the appropriate option in the graphical installer.

Note that the QApplication instance must be created before this function is called.

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

new bool QtGui.QImageReader.SupportsAnimation

(

)

Returns true if the image format supports animation; otherwise, false is returned.

This function was introduced in Qt 4.1.

See also QMovie::supportedFormats().

new bool QtGui.QImageReader.SupportsOption

(

QImageIOHandler.ImageOption

option

)

Returns true if the reader 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()), and the BMP format allows you to determine the image's size without loading the whole image into memory (see size()).

QImageReader reader(":/image.png");

if (reader.supportsOption(QImageIOHandler::Size))

qDebug() << "Size:" << reader.size();

This function was introduced in Qt 4.2.

See also QImageWriter::supportsOption().

new string QtGui.QImageReader.Text

(

string

key

)

Returns the image text associated with key.

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

This function was introduced in Qt 4.1.

See also textKeys() and QImageWriter::setText().

new System.Collections.Generic.List<string> QtGui.QImageReader.TextKeys

(

)

Returns the text keys for this image. You can use these keys with text() to list the image text for a certain key.

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

This function was introduced in Qt 4.1.

See also text(), QImageWriter::setText(), and QImage::textKeys().

Member Data Documentation

SmokeInvocation QtGui.QImageReader.interceptor

protected

Property Documentation

new bool QtGui.QImageReader.AutoDetectImageFormat

getset

Returns true if image format autodetection is enabled on this image reader; otherwise returns false. By default, autodetection is enabled.

If enabled is true, image format autodetection is enabled; otherwise, it is disabled. By default, autodetection is enabled.

QImageReader uses an extensive approach to detecting the image format; firstly, if you pass a file name to QImageReader, it will attempt to detect the file extension if the given file name does not point to an existing file, by appending supported default extensions to the given file name, one at a time. It then uses the following approach to detect the image format:

Image plugins are queried first, based on either the optional format string, or the file name suffix (if the source device is a file). No content detection is done at this stage. QImageReader will choose the first plugin that supports reading for this format.

If no plugin supports the image format, Qt's built-in handlers are checked based on either the optional format string, or the file name suffix.

If no capable plugins or built-in handlers are found, each plugin is tested by inspecting the content of the data stream.

If no plugins could detect the image format based on data contents, each built-in image handler is tested by inspecting the contents.

Finally, if all above approaches fail, QImageReader will report failure when trying to read the image.

By disabling image format autodetection, QImageReader will only query the plugins and built-in handlers based on the format string (i.e., no file name extensions are tested).

new QColor QtGui.QImageReader.BackgroundColor

getset

Returns the background color that's used when reading an image. If the image format does not support setting the background color an invalid color is returned.

This function was introduced in Qt 4.1.

Sets the background color to color. Image formats that support this operation are expected to initialize the background to color before reading an image.

This function was introduced in Qt 4.1.

new QRect QtGui.QImageReader.ClipRect

getset

Returns the clip rect (also known as the ROI, or Region Of Interest) of the image. If no clip rect has been set, an invalid QRect is returned.

Sets the image clip rect (also known as the ROI, or Region Of Interest) to rect. The coordinates of rect are relative to the untransformed image size, as returned by size().

new bool QtGui.QImageReader.DecideFormatFromContent

getset

Returns whether the image reader should decide which plugin to use only based on the contents of the datastream rather than on the file extension.

If ignored is set to true, then the image reader will ignore specified formats or file extensions and decide which plugin to use only based on the contents in the datastream.

Setting this flag means that all image plugins gets loaded. Each plugin will read the first bytes in the image data and decide if the plugin is compatible or not.

This also disables auto detecting the image format.

new QIODevice QtGui.QImageReader.Device

getset

Returns the device currently assigned to QImageReader, or 0 if no device has been assigned.

Sets QImageReader's device to device. If a device has already been set, the old device is removed from QImageReader and is otherwise left unchanged.

If the device is not already open, QImageReader will attempt to open the device in QIODevice::ReadOnly 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.

new string QtGui.QImageReader.FileName

getset

If the currently assigned device is a QFile, or if setFileName() has been called, this function returns the name of the file QImageReader reads from. Otherwise (i.e., if no device has been assigned or the device is not a QFile), an empty QString is returned.

Sets the file name of QImageReader to fileName. Internally, QImageReader will create a QFile object and open it in QIODevice::ReadOnly mode, and use this when reading images.

If fileName does not include a file extension (e.g., .png or .bmp), QImageReader will cycle through all supported extensions until it finds a matching file.

new QByteArray QtGui.QImageReader.Format

getset

Returns the format QImageReader uses for reading images.

You can call this function after assigning a device to the reader to determine the format of the device. For example:

QImageReader reader("image.png");

// reader.format() == "png"

If the reader cannot read any image from the device (e.g., there is no image there, or the image has already been read), or if the format is unsupported, this function returns an empty QByteArray().

Sets the format QImageReader will use when reading images, to format. format is a case insensitive text string. Example:

QImageReader reader;

reader.setFormat("png"); // same as reader.setFormat("PNG");

You can call supportedImageFormats() for the full list of formats QImageReader supports.

new int QtGui.QImageReader.Quality

getset

Returns the quality level of the image.

This function was introduced in Qt 4.2.

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).

This function was introduced in Qt 4.2.

new QRect QtGui.QImageReader.ScaledClipRect

getset

Returns the scaled clip rect of the image.

Sets the scaled clip rect to rect. The scaled clip rect is the clip rect (also known as ROI, or Region Of Interest) that is applied after the image has been scaled.

new QSize QtGui.QImageReader.ScaledSize

getset

Returns the scaled size of the image.

Sets the scaled size of the image to size. The scaling is performed after the initial clip rect, but before the scaled clip rect is applied. The algorithm used for scaling depends on the image format. By default (i.e., if the image format does not support scaling), QImageReader will use QImage::scale() with Qt::SmoothScaling.

virtual System.IntPtr QtGui.QImageReader.SmokeObject

getset