The QImageReader class provides a format independent interface for reading images from files or other devices. 更多...
The QImageReader class provides a format independent interface for reading images from files or other devices.
读取图像的最常见方式是透过 QImage and QPixmap 's constructors, or by calling QImage.load () 和 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 ()，和 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.
若读取图像时发生任何错误， read () 将返回 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.
调用 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, 通过调用 setAutoDetectImageFormat ().
This enum describes the different types of errors that can occur when reading images with QImageReader .
| 常量 | 值 | 描述 |
|---|---|---|
| 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 Qt. |
| 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 | Qt 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 . |
构造空 QImageReader object. Before reading an image, call setDevice () 或 setFileName ().
构造 QImageReader object with the device device 和图像格式 format .
构造 QImageReader object with the file name fileName 和图像格式 format .
另请参阅 setFileName ().
Returns true if image format autodetection is enabled on this image reader; otherwise returns false. By default, autodetection is enabled.
另请参阅 setAutoDetectImageFormat ().
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.
该函数在 Qt 4.1 引入。
另请参阅 setBackgroundColor () 和 read ().
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.
另请参阅 read () 和 supportedImageFormats ().
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 被返回。
另请参阅 setClipRect ().
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.
此函数返回 -1，若发生错误。
另请参阅 supportsAnimation (), QImageIOHandler.currentImageNumber (), and canRead ().
For image formats that support animation, this function returns the rect for the current frame. Otherwise, a null rect is returned.
另请参阅 supportsAnimation () 和 QImageIOHandler.currentImageRect ().
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.
另请参阅 setDecideFormatFromContent ().
Returns the device currently assigned to QImageReader , or 0 if no device has been assigned.
另请参阅 setDevice ().
返回最后发生的错误类型。
另请参阅 ImageReaderError and errorString ().
Returns a human readable description of the last error that occurred.
另请参阅 error ().
若目前赋值设备是 QFile ，或者若 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 被返回。
另请参阅 setFileName () 和 setDevice ().
返回格式 QImageReader 用于读取图像。
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().
另请参阅 setFormat () 和 supportedImageFormats ().
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.
此函数返回 -1，若发生错误。
另请参阅 supportsAnimation (), QImageIOHandler.imageCount (), and canRead ().
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.
该函数在 Qt 4.5 引入。
另请参阅 QImageIOHandler.ImageOption , QImageIOHandler.option ()，和 QImageIOHandler.supportsOption ().
If supported, this function returns the image format of the file fileName . Otherwise, an empty string is returned.
If supported, this function returns the image format of the device device . Otherwise, an empty string is returned.
另请参阅 QImageReader.autoDetectImageFormat ().
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.
另请参阅 jumpToNextImage () 和 QImageIOHandler.jumpToImage ().
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.
默认实现调用 read (), then discards the resulting image, but the image handler may have a more efficient way of implementing this operation.
另请参阅 jumpToImage () 和 QImageIOHandler.jumpToNextImage ().
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 () 将返回 false。
另请参阅 supportsAnimation (), QImageIOHandler.loopCount (), and canRead ().
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 被返回。
此函数返回 -1，若发生错误。
另请参阅 supportsAnimation (), QImageIOHandler.nextImageDelay (), and canRead ().
Returns the quality level of the image.
该函数在 Qt 4.2 引入。
另请参阅 setQuality ().
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.
另请参阅 canRead (), supportedImageFormats (), supportsAnimation ()，和 QMovie .
这是重载函数。
Reads an image from the device into image , which must point to a QImage . Returns true on success; otherwise, returns false.
若 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.
另请参阅 canRead (), supportedImageFormats (), supportsAnimation ()，和 QMovie .
Returns the scaled clip rect of the image.
另请参阅 setScaledClipRect ().
返回图像的比例缩放尺寸。
另请参阅 setScaledSize ().
若 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:
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).
另请参阅 autoDetectImageFormat (), QImageIOHandler.canRead ()，和 QImageIOPlugin.capabilities ().
Sets the background color to color . Image formats that support this operation are expected to initialize the background to color before reading an image.
该函数在 Qt 4.1 引入。
另请参阅 backgroundColor () 和 read ().
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 ().
另请参阅 clipRect (), setScaledSize ()，和 setScaledClipRect ().
若 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.
这还禁用自动检测图像格式。
另请参阅 decideFormatFromContent ().
集 QImageReader 's device to device . If a device has already been set, the old device is removed from QImageReader and is otherwise left unchanged.
若设备尚未打开， 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.
另请参阅 device () and setFileName ().
Sets the file name of QImageReader to fileName . 内部， QImageReader will create a QFile object and open it in QIODevice.ReadOnly mode, and use this when reading images.
若 fileName does not include a file extension (e.g., .png or .bmp), QImageReader will cycle through all supported extensions until it finds a matching 文件。
另请参阅 fileName (), setDevice ()，和 supportedImageFormats ().
设置格式 QImageReader will use when reading images, to format . format 是 case insensitive text string. Example:
QImageReader reader; reader.setFormat("png"); // same as reader.setFormat("PNG");
可以调用 supportedImageFormats () for the full list of formats QImageReader 支持。
另请参阅 format ().
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).
该函数在 Qt 4.2 引入。
另请参阅 quality ().
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.
另请参阅 scaledClipRect () 和 setScaledSize ().
将图像的比例缩放尺寸设为 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.
另请参阅 scaledSize (), setClipRect ()，和 setScaledClipRect ().
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.
另请参阅 QImageIOHandler.ImageOption , QImageIOHandler.option ()，和 QImageIOHandler.supportsOption ().
Returns the list of image formats supported by QImageReader .
默认情况下，Qt 可以读取以下格式：
| Format | 描述 |
|---|---|
| BMP | Windows 位图 |
| GIF | Graphic Interchange Format (图形互换格式) 可选 |
| JPG | Joint Photographic Experts Group (联合摄影专家组) |
| JPEG | Joint Photographic Experts Group (联合摄影专家组) |
| MNG | 多图像网络图形 |
| PNG | Portable Network Graphics (便携式网络图形) |
| PBM | Portable Bitmap (便携式位图) |
| PGM | Portable Graymap (便携式灰度图) |
| PPM | Portable Pixmap (便携式像素图) |
| TIFF | 标签化图像文件格式 |
| XBM | X11 Bitmap (X11 位图) |
| XPM | X11 Pixmap (X11 像素图) |
| SVG | SVG (可伸缩向量图形) |
| 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 到 configure script or check the appropriate option in the graphical installer.
注意： QApplication 实例必须被创建在调用此函数之前。
另请参阅 setFormat (), QImageWriter.supportedImageFormats (), and QImageIOPlugin .
Returns true if the image format supports animation; otherwise, false is returned.
该函数在 Qt 4.1 引入。
另请参阅 QMovie.supportedFormats ().
Returns true if the reader supports option ；否则 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();
该函数在 Qt 4.2 引入。
另请参阅 QImageWriter.supportsOption ().
返回的图像文本关联 key .
支持此选项的实现是透过 QImageIOHandler.Description .
该函数在 Qt 4.1 引入。
另请参阅 textKeys () 和 QImageWriter.setText ().
Returns the text keys for this image. You can use these keys with text () to list the image text for a certain key.
支持此选项的实现是透过 QImageIOHandler.Description .
该函数在 Qt 4.1 引入。
另请参阅 text (), QImageWriter.setText (), and QImage.textKeys ().
