QImageWriter class provides a format independent interface for writing images to files or other devices. 更多...
Header: | #include <QImageWriter> |
qmake: | QT += gui |
注意: 此类的所有函数 可重入 .
enum | ImageWriterError { DeviceError, UnsupportedFormatError, InvalidImageError, UnknownError } |
QImageWriter () | |
QImageWriter (QIODevice * device , const QByteArray & format ) | |
QImageWriter (const QString & fileName , const QByteArray & format = QByteArray()) | |
~QImageWriter () | |
bool | canWrite () const |
int | compression () const |
QIODevice * | device () const |
QImageWriter::ImageWriterError | error () const |
QString | errorString () const |
QString | fileName () const |
QByteArray | format () const |
float | gamma () const |
bool | optimizedWrite () const |
bool | progressiveScanWrite () const |
int | quality () const |
void | setCompression (int compression ) |
void | setDevice (QIODevice * device ) |
void | setFileName (const QString & fileName ) |
void | setFormat (const QByteArray & format ) |
void | setGamma (float gamma ) |
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 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 () 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 the gamma level (by calling
setGamma
()) and 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.
例如:
QString imagePath(QStringLiteral("path/image.jpeg")); QImage image(64, 64, QImage::Format_RGB32); image.fill(Qt::red); { QImageWriter writer(imagePath); writer.write(image); } QFile::rename(imagePath, QStringLiteral("path/other_image.jpeg"));
另请参阅 QImageReader , QImageIOHandler ,和 QImageIOPlugin .
This enum describes errors that can occur when writing images with QImageWriter .
常量 | 值 | 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 . |
构造空 QImageWriter object. Before writing, you must call setFormat () to set an image format, then setDevice () 或 setFileName ().
构造 QImageWriter object using the device device and image format format .
构造 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 .
销毁 QImageWriter 对象。
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 ().
Returns the compression of the image.
另请参阅 setCompression ().
Returns the device currently assigned to QImageWriter , 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 ImageWriterError and errorString ().
返回最近发生错误的人类可读描述。
另请参阅 error ().
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 被返回。
另请参阅 setFileName () 和 setDevice ().
Returns the format QImageWriter uses for writing images.
另请参阅 setFormat ().
Returns the gamma level of the image.
另请参阅 setGamma ().
[static]
QList
<
QByteArray
> QImageWriter::
imageFormatsForMimeType
(const
QByteArray
&
mimeType
)
Returns the list of image formats corresponding to mimeType .
注意: QGuiApplication instance must be created before this function is called.
This function was introduced in Qt 5.12.
另请参阅 supportedImageFormats () 和 supportedMimeTypes ().
Returns whether optimization has been turned on for writing the image.
This function was introduced in Qt 5.5.
另请参阅 setOptimizedWrite ().
Returns whether the image should be written as a progressive image.
This function was introduced in Qt 5.5.
另请参阅 setProgressiveScanWrite ().
返回图像格式的品质设置。
另请参阅 setQuality ().
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).
另请参阅 compression ().
集 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 ().
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 ().
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");
可以调用 supportedImageFormats () for the full list of formats QImageWriter supports.
另请参阅 format ().
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.
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。
This function was introduced in Qt 5.5.
另请参阅 optimizedWrite ().
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。
This function was introduced in Qt 5.5.
另请参阅 progressiveScanWrite ().
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 ().
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)) writer.setSubType("A8R8G8B8"); writer.write(image);
This function was introduced in Qt 5.4.
另请参阅 subType ().
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 .
This function was introduced in Qt 4.1.
另请参阅 QImage::setText () 和 QImageReader::text ().
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.
This function was introduced in Qt 5.5.
另请参阅 transformation () 和 write ().
Returns the subtype of the image.
This function was introduced in Qt 5.4.
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:
Format | MIME type | 描述 |
---|---|---|
BMP | image/bmp | Windows Bitmap |
JPG | image/jpeg | Joint Photographic Experts Group |
PNG | image/png | Portable Network Graphics |
PBM | image/x-portable-bitmap | Portable Bitmap |
PGM | image/x-portable-graymap | Portable Graymap |
PPM | image/x-portable-pixmap | Portable Pixmap |
XBM | image/x-xbitmap | X11 Bitmap |
XPM | image/x-xpixmap | X11 Pixmap |
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 instance must be created before this function is called.
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 instance must be created before this function is called.
另请参阅 supportedImageFormats () 和 QImageReader::supportedMimeTypes ().
Returns the list of subtypes supported by an image.
This function was introduced in Qt 5.4.
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.
This function was introduced in Qt 4.2.
另请参阅 QImageReader::supportsOption () 和 setFormat ().
Returns the transformation and orientation the image has been set to written with.
This function was introduced in Qt 5.5.
另请参阅 setTransformation ().
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 ().