The QImageReader class provides a format independent interface for reading images from files or other devices. More...
Public Types | |
| enum | ImageReaderError |
Static Public Methods | |
| static QString | imageFormat (const QString &fileName) |
| static QString | imageFormat (QIODevice *device) |
| static QList< QString > | supportedImageFormats () |
| static QList< QString > | supportedMimeTypes () |
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, QImageIOPlugin
Member Enumeration Documentation
This enum describes the different types of errors that can occur when reading images with QImageReader.
| Constant | Value | Description |
|---|---|---|
QImageReader::FileNotFoundError | 1 | 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 CopperSpice. |
QImageReader::DeviceError | 2 | QImageReader encountered a device error when reading the image. You can consult your particular device for more details on what went wrong. |
QImageReader::UnsupportedFormatError | 3 | CopperSpice does not support the requested image format. |
QImageReader::InvalidDataError | 4 | The image data was invalid, and QImageReader was unable to read an image from it. The can happen if the image file is damaged. |
QImageReader::UnknownError | 0 | An unknown error occurred. If you get this value after calling read(), it is most likely caused by a bug in QImageReader. |
Constructor & Destructor Documentation
| QImageReader::QImageReader | ( | ) |
Constructs an empty QImageReader object. Before reading an image, call setDevice() or setFileName().
Constructs a QImageReader object using the given device and the image format.
|
explicit |
Constructs a QImageReader object with the file name fileName and the image format.
- See also
- setFileName()
| QImageReader::~QImageReader | ( | ) |
Destructs the QImageReader object.
Method Documentation
| bool QImageReader::autoDetectImageFormat | ( | ) | const |
Returns true if image format autodetection is enabled on this image reader, otherwise returns false. By default, autodetection is enabled.
- See also
- setAutoDetectImageFormat()
| bool QImageReader::autoTransform | ( | ) | const |
Returns true if the image handler will apply transformation metadata on read().
- See also
- setAutoTransform(), transformation(), read()
| QColor QImageReader::backgroundColor | ( | ) | const |
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.
- See also
- setBackgroundColor(), read()
| bool QImageReader::canRead | ( | ) | const |
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(), supportedImageFormats()
| QRect QImageReader::clipRect | ( | ) | const |
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.
- See also
- setClipRect()
| int QImageReader::currentImageNumber | ( | ) | const |
For image formats that support animation, this function returns the sequence number of the current frame. If the image format does not support animation, 0 is returned.
This function returns -1 if an error occurred.
| QRect QImageReader::currentImageRect | ( | ) | const |
For image formats that support animation, this function returns the rect for the current frame. Otherwise, a null rect is returned.
| bool QImageReader::decideFormatFromContent | ( | ) | const |
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.
- See also
- setDecideFormatFromContent()
| QIODevice * QImageReader::device | ( | ) | const |
Returns the device currently assigned to QImageReader or a nullptr if no device has been assigned.
- See also
- setDevice()
| ImageReaderError QImageReader::error | ( | ) | const |
Returns the type of error that occurred last.
- See also
- ImageReaderError, errorString()
| QString QImageReader::errorString | ( | ) | const |
Returns a human readable description of the last error that occurred.
- See also
- error()
| QString QImageReader::fileName | ( | ) | const |
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.
- See also
- setFileName(), setDevice()
| QString QImageReader::format | ( | ) | const |
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.
If the reader can not 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 method returns an empty QString.
- See also
- setFormat(), supportedImageFormats()
| float QImageReader::gamma | ( | ) | const |
Returns the gamma level of the decoded image. If setGamma() has been called and gamma correction is supported it will return the gamma set. If gamma level is not supported by the image format, 0.0 is returned.
| int QImageReader::imageCount | ( | ) | const |
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.
| QImage::Format QImageReader::imageFormat | ( | ) | const |
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.
If supported, this method returns the image format of the file fileName. Otherwise, an empty string is returned.
If supported, this method returns the image format of the device. Otherwise, an empty string is returned.
| bool QImageReader::jumpToImage | ( | int | imageNumber | ) |
For image formats that support animation, this method skips to the image whose sequence number is imageNumber, returning true if successful or false if the corresponding image can not be found.
The next call to read() will attempt to read this image.
| bool 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.
| int QImageReader::loopCount | ( | ) | const |
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.
| int QImageReader::nextImageDelay | ( | ) | const |
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 does not support animation, 0 is returned.
This function returns -1 if an error occurred.
| int QImageReader::quality | ( | ) | const |
Returns the quality level of the image.
- See also
- setQuality()
| QImage 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.
| bool QImageReader::read | ( | QImage * | image | ) |
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.
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.
| QRect QImageReader::scaledClipRect | ( | ) | const |
Returns the scaled clip rect of the image.
- See also
- setScaledClipRect()
| QSize QImageReader::scaledSize | ( | ) | const |
Returns the scaled size of the image.
- See also
- setScaledSize()
| void QImageReader::setAutoDetectImageFormat | ( | bool | 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, the CopperSpice 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).
| void QImageReader::setAutoTransform | ( | bool | enabled | ) |
Determines that images returned by read() should have transformation metadata automatically applied if enabled is true.
- See also
- autoTransform(), transformation(), read()
| void QImageReader::setBackgroundColor | ( | const QColor & | color | ) |
Sets the background color to color. Image formats that support this operation are expected to initialize the background to color before reading an image.
- See also
- backgroundColor(), read()
| void QImageReader::setClipRect | ( | const QRect & | rect | ) |
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().
- See also
- clipRect(), setScaledSize(), setScaledClipRect()
| void QImageReader::setDecideFormatFromContent | ( | bool | ignored | ) |
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.
- See also
- decideFormatFromContent()
| void QImageReader::setDevice | ( | QIODevice * | device | ) |
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.
- See also
- device(), setFileName()
| void QImageReader::setFileName | ( | const QString & | fileName | ) |
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.
- See also
- fileName(), setDevice(), supportedImageFormats()
| void QImageReader::setFormat | ( | const QString & | format | ) |
Sets the format QImageReader will use when reading images to format. The format is a case insensitive text string.
You can call supportedImageFormats() for the full list of formats QImageReader supports.
- See also
- format()
| void QImageReader::setGamma | ( | float | gamma | ) |
This is an image format specific function that forces images with gamma information to be corrected to gamma. For image formats that do not support gamma correction, this value is ignored.
To gamma correct to a standard PC color-space, set gamma to 1/2.2.
- See also
- gamma()
| void QImageReader::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()
| void QImageReader::setScaledClipRect | ( | const QRect & | rect | ) |
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.
- See also
- scaledClipRect(), setScaledSize()
| void QImageReader::setScaledSize | ( | const QSize & | size | ) |
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.
- See also
- scaledSize(), setClipRect(), setScaledClipRect()
| QSize QImageReader::size | ( | ) | const |
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. the CopperSpice built-in image handlers all support this feature, but custom image format plugins are not required to do so.
| QByteArray QImageReader::subType | ( | ) | const |
Returns the subtype of the image.
Returns the list of image formats supported by QImageReader. The QApplication instance must be created before this method is called.
By default CopperSpice can read the following formats.
| Format | Description |
|---|---|
| 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 the CsSvg library.
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.
Returns the list of MIME types supported by QImageReader. The QApplication instance must be created before this method is called.
| QList< QByteArray > QImageReader::supportedSubTypes | ( | ) | const |
Returns the list of subtypes supported by an image.
| bool QImageReader::supportsAnimation | ( | ) | const |
Returns true if the image format supports animation, otherwise false is returned.
- See also
- QMovie::supportedFormats()
| bool QImageReader::supportsOption | ( | QImageIOHandler::ImageOption | option | ) | const |
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()).
- See also
- QImageWriter::supportsOption()
Returns the image text associated with key.
Support for this option is implemented through QImageIOHandler::Description.
- See also
- textKeys(), QImageWriter::setText()
| QStringList QImageReader::textKeys | ( | ) | const |
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.
- See also
- text(), QImageWriter::setText(), QImage::textKeys()
| QImageIOHandler::Transformations QImageReader::transformation | ( | ) | const |
Returns the transformation metadata of the image, including image orientation. If the format does not support transformation metadata, QImageIOHandler::TransformationNone is returned.
- See also
- setAutoTransform(), autoTransform()
- Generated on Thu Feb 29 2024 16:30 by
1.6.0