QImageWriter Class

The QImageWriter class provides a format independent interface for writing images to files or other devices. 更多...

Header: #include <QImageWriter>
CMake: find_package(Qt6 COMPONENTS Gui REQUIRED)
target_link_libraries(mytarget PRIVATE Qt6::Gui)
qmake: QT += gui

注意: 此类的所有函数 可重入 .


enum ImageWriterError { DeviceError, UnsupportedFormatError, InvalidImageError, UnknownError }


QImageWriter (const QString & fileName , const QByteArray & format = QByteArray())
QImageWriter (QIODevice * device , const QByteArray & format )
QImageWriter ()
~QImageWriter ()
bool canWrite () const
int 压缩 () const
QIODevice * device () const
QImageWriter::ImageWriterError error () const
QString errorString () const
QString fileName () const
QByteArray format () const
bool optimizedWrite () const
bool progressiveScanWrite () const
int quality () const
void setCompression (int 压缩 )
void setDevice (QIODevice * device )
void setFileName (const QString & fileName )
void setFormat (const QByteArray & format )
void setOptimizedWrite (bool optimize )
void setProgressiveScanWrite (bool progressive )
void setQuality (int quality )
void setSubType (const QByteArray & type )
void setText (const QString & key , const QString & text )
void setTransformation (QImageIOHandler::Transformations transform )
QByteArray subType () const
QList<QByteArray> supportedSubTypes () const
bool supportsOption (QImageIOHandler::ImageOption option ) const
QImageIOHandler::Transformations transformation () const
bool write (const QImage & image )


QList<QByteArray> imageFormatsForMimeType (const QByteArray & mimeType )
QList<QByteArray> supportedImageFormats ()
QList<QByteArray> supportedMimeTypes ()


QImageWriter supports setting format specific options, such as compression level and quality, prior to storing the image. If you do not need such options, you can use QImage::save () 或 QPixmap::save () 代替。

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 quality (by calling setQuality ()). canWrite () 返回 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.

调用 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.

注意: QImageWriter assumes exclusive control over the file or device that is assigned. Any attempts to modify the assigned file or device during the lifetime of the QImageWriter object will yield undefined results. If immediate access to a resource is desired, the use of a scope is the recommended method.


QString imagePath(QStringLiteral("path/image.jpeg"));
QImage image(64, 64, QImage::Format_RGB32);
    QImageWriter writer(imagePath);

另请参阅 QImageReader , QImageIOHandler , QImageIOPlugin ,和 QColorSpace .


enum QImageWriter:: ImageWriterError

This enum describes errors that can occur when writing images with QImageWriter .

常量 描述
QImageWriter::DeviceError 1 QImageWriter encountered a device error when writing the image data. Consult your device for more details on what went wrong.
QImageWriter::UnsupportedFormatError 2 Qt 不支持请求的图像格式。
QImageWriter::InvalidImageError 3 An attempt was made to write an invalid QImage . An example of an invalid image would be a null QImage .
QImageWriter::UnknownError 0 An unknown error occurred. If you get this value after calling write (), it is most likely caused by a bug in QImageWriter .


QImageWriter:: QImageWriter (const QString & fileName , const QByteArray & format = QByteArray())

Constructs a QImageWriter objects that will write to a file with the name fileName , using the image format format 。若 format is not provided, QImageWriter will detect the image format by inspecting the extension of fileName .

QImageWriter:: QImageWriter ( QIODevice * device , const QByteArray & format )

Constructs a QImageWriter object using the device device and image format format .

QImageWriter:: QImageWriter ()

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

QImageWriter:: ~QImageWriter ()

销毁 QImageWriter 对象。

bool QImageWriter:: canWrite () const

返回 true if QImageWriter can write the image; i.e., the image format is supported and the assigned device is open for reading.

另请参阅 write (), setDevice (),和 setFormat ().

int QImageWriter:: 压缩 () const

Returns the compression of the image.

另请参阅 setCompression ().

QIODevice *QImageWriter:: device () const

Returns the device currently assigned to QImageWriter ,或 nullptr 若没有设备被赋值。

另请参阅 setDevice ().

QImageWriter::ImageWriterError QImageWriter:: error () const


另请参阅 ImageWriterError and errorString ().

QString QImageWriter:: errorString () const


另请参阅 error ().

QString QImageWriter:: fileName () const

若目前赋值设备是 QFile ,或者若 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 被返回。

另请参阅 setFileName () 和 setDevice ().

QByteArray QImageWriter:: format () const

返回格式 QImageWriter uses for writing images.

另请参阅 setFormat ().

[static, since 5.12] QList < QByteArray > QImageWriter:: imageFormatsForMimeType (const QByteArray & mimeType )

Returns the list of image formats corresponding to mimeType .

注意, QGuiApplication 实例必须被创建在调用此函数之前。

该函数在 Qt 5.12 引入。

另请参阅 supportedImageFormats () 和 supportedMimeTypes ().

[since 5.5] bool QImageWriter:: optimizedWrite () const

Returns whether optimization has been turned on for writing the image.

该函数在 Qt 5.5 引入。

另请参阅 setOptimizedWrite ().

[since 5.5] bool QImageWriter:: progressiveScanWrite () const

Returns whether the image should be written as a progressive image.

该函数在 Qt 5.5 引入。

另请参阅 setProgressiveScanWrite ().

int QImageWriter:: quality () const


另请参阅 setQuality ().

void QImageWriter:: setCompression ( int 压缩 )

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

另请参阅 压缩 ().

void QImageWriter:: setDevice ( QIODevice * device )

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

若设备尚未打开, 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.

另请参阅 device () 和 setFileName ().

void QImageWriter:: setFileName (const QString & 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.

另请参阅 fileName () 和 setDevice ().

void QImageWriter:: setFormat (const QByteArray & format )

设置格式 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");

可以调用 supportedImageFormats () for the full list of formats QImageWriter 支持。

另请参阅 format ().

[since 5.5] void QImageWriter:: setOptimizedWrite ( bool optimize )

This is an image format-specific function which sets the optimize flags when writing images. For image formats that do not support setting an optimize flag, this value is ignored.

默认为 false。

该函数在 Qt 5.5 引入。

另请参阅 optimizedWrite ().

[since 5.5] void QImageWriter:: setProgressiveScanWrite ( bool progressive )

This is an image format-specific function which turns on progressive scanning when writing images. For image formats that do not support setting a progressive scan flag, this value is ignored.

默认为 false。

该函数在 Qt 5.5 引入。

另请参阅 progressiveScanWrite ().

void QImageWriter:: setQuality ( int quality )

将图像格式的品质设置设为 quality .

Some image formats, in particular lossy ones, entail a tradeoff between a) visual quality of the resulting image, and b) encoding execution time and compression level. This function sets the level of that tradeoff for image formats that support it. For other formats, 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 visual quality, high compression) to 100 (high visual quality, low compression).

另请参阅 quality ().

[since 5.4] void QImageWriter:: setSubType (const QByteArray & type )

This is an image format specific function that sets the subtype of the image to type . Subtype can be used by a handler to determine which format it should use while saving the image.

For example, saving an image in DDS format with A8R8G8R8 subtype:

QImageWriter writer("some/image.dds");
if (writer.supportsOption(QImageIOHandler::SubType))

该函数在 Qt 5.4 引入。

另请参阅 subType ().

void QImageWriter:: setText (const QString & key , const QString & 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");

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 ().

支持此选项的实现是透过 QImageIOHandler::Description .

另请参阅 QImage::setText () 和 QImageReader::text ().

[since 5.5] void QImageWriter:: setTransformation ( QImageIOHandler::Transformations transform )

Sets the image transformations metadata including orientation to transform .

If transformation metadata is not supported by the image format, the transform is applied before writing.

该函数在 Qt 5.5 引入。

另请参阅 transformation () 和 write ().

[since 5.4] QByteArray QImageWriter:: subType () const


该函数在 Qt 5.4 引入。

另请参阅 setSubType ().

[static] QList < QByteArray > QImageWriter:: supportedImageFormats ()

Returns the list of image formats supported by QImageWriter .

By default, Qt can write the following formats:

格式 MIME 类型 描述
BMP image/bmp Windows 位图
JPG image/jpeg Joint Photographic Experts Group (联合摄影专家组)
PNG image/png PNG (便携式网络图形)
PBM image/x-portable-bitmap PBM (便携式位图)
PGM image/x-portable-graymap PGM (便携式灰度图)
PPM image/x-portable-pixmap Portable Pixmap (便携式像素图)
XBM image/x-xbitmap X11 Bitmap (X11 位图)
XPM image/x-xpixmap X11 Pixmap (X11 像素图)

Reading and writing SVG files is supported through the Qt SVG 模块。 Qt Image Formats module provides support for additional image formats.

注意, QApplication 实例必须被创建在调用此函数之前。

另请参阅 setFormat (), QImageReader::supportedImageFormats (),和 QImageIOPlugin .

[static] QList < QByteArray > QImageWriter:: supportedMimeTypes ()

Returns the list of MIME types supported by QImageWriter .

注意, QApplication 实例必须被创建在调用此函数之前。

另请参阅 supportedImageFormats () 和 QImageReader::supportedMimeTypes ().

[since 5.4] QList < QByteArray > QImageWriter:: supportedSubTypes () const


该函数在 Qt 5.4 引入。

bool QImageWriter:: supportsOption ( QImageIOHandler::ImageOption option ) const

返回 true if the writer supports option ;否则返回 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.

另请参阅 QImageReader::supportsOption () 和 setFormat ().

[since 5.5] QImageIOHandler::Transformations QImageWriter:: transformation () const

Returns the transformation and orientation the image has been set to written with.

该函数在 Qt 5.5 引入。

另请参阅 setTransformation ().

bool QImageWriter:: write (const QImage & image )

写入图像 image to the assigned device or file name. Returns true 当成功时;否则返回 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.

另请参阅 canWrite (), error (),和 errorString ().