QImageIOHandler¶

PyQt5.QtGui.QImageIOHandler

Description¶

The QImageIOHandler class defines the common image I/O interface for all image formats in Qt.

Qt uses QImageIOHandler for reading and writing images through QImageReader and QImageWriter. You can also derive from this class to write your own image format handler using Qt’s plugin mechanism.

Call setDevice() to assign a device to the handler, and setFormat() to assign a format to it. One QImageIOHandler may support more than one image format. canRead() returns true if an image can be read from the device, and read() and write() return true if reading or writing an image was completed successfully.

QImageIOHandler also has support for animations formats, through the functions loopCount(), imageCount(), nextImageDelay() and currentImageNumber().

In order to determine what options an image handler supports, Qt will call supportsOption() and setOption(). Make sure to reimplement these functions if you can provide support for any of the options in the ImageOption enum.

To write your own image handler, you must at least reimplement canRead() and read(). Then create a QImageIOPlugin that can create the handler. Finally, install your plugin, and QImageReader and QImageWriter will then automatically load the plugin, and start using it.

Classes¶

Transformations

Enums¶

ImageOption

This enum describes the different options supported by QImageIOHandler. Some options are used to query an image for properties, and others are used to toggle the way in which an image should be written.

Member	Value	Description
Animation	12	Image formats that support animation return true for this value in supportsOption(); otherwise, false is returned.
BackgroundColor	13	Certain image formats allow the background color to be specified. A handler that supports initializes the background color to this option (a QColor) when reading an image.
ClipRect	1	The clip rect, or ROI (Region Of Interest). A handler that supports this option is expected to only read the provided QRect area from the original image in read(), before any other transformation is applied.
CompressionRatio	5	The compression ratio of the image data. A handler that supports this option is expected to set its compression rate depending on the value of this option (an int) when writing.
Description	2	The image description. Some image formats, such as GIF and PNG, allow embedding of text or comments into the image data (e.g., for storing copyright information). It’s common that the text is stored in key-value pairs, but some formats store all text in one continuous block. QImageIOHandler returns the text as one QString, where keys and values are separated by a ‘:’, and keys-value pairs are separated by two newlines (\n\n). For example, “Title: Sunset\n\nAuthor: Jim Smith\nSarah Jones\n\n”. Formats that store text in a single block can use “Description” as the key.
Endianness	11	The endianness of the image. Certain image formats can be stored as BigEndian or LittleEndian. A handler that supports Endianness uses the value of this option to determine how the image should be stored.
Gamma	6	The gamma level of the image. A handler that supports this option is expected to set the image gamma level depending on the value of this option (a float) when writing.
ImageTransformation	TODO	. A handler which supports this option can read the transformation metadata of an image. A handler that supports this option should not apply the transformation itself.
IncrementalReading	10	A handler that supports this option is expected to read the image in several passes, as if it was an animation. QImageReader will treat the image as an animation.
Name	8	The name of the image. A handler that supports this option is expected to read the name from the image metadata and return this as a QString, or when writing an image it is expected to store the name in the image metadata.
OptimizedWrite	TODO	. A handler which supports this option is expected to turn on optimization flags when writing.
ProgressiveScanWrite	TODO	. A handler which supports this option is expected to write the image as a progressive scan image.
Quality	7	The quality level of the image. A handler that supports this option is expected to set the image quality level depending on the value of this option (an int) when writing.
ScaledClipRect	3	The scaled clip rect (or ROI, Region Of Interest) of the image. A handler that supports this option is expected to apply the provided clip rect (a QRect), after applying any scaling (ScaleSize) or regular clipping (). If the handler does not support this option, QImageReader will apply the scaled clip rect after the image has been read.
ScaledSize	4	The scaled size of the image. A handler that supports this option is expected to scale the image to the provided size (a QSize), after applying any clip rect transformation (). If the handler does not support this option, QImageReader will perform the scaling after the image has been read.
Size	0	The original size of an image. A handler that supports this option is expected to read the size of the image from the image metadata, and return this size from option() as a QSize.
SubType	9	The subtype of the image. A handler that supports this option can use the subtype value to help when reading and writing images. For example, a PPM handler may have a subtype value of “ppm” or “ppmraw”.
SupportedSubTypes	TODO	Image formats that support different saving variants should return a list of supported variant names (QList<QByteArray>) in this option.
TransformedByDefault	TODO	. A handler that reports support for this feature will have image transformation metadata applied by default on read.

Transformation

TODO

Member	Value	Description
TransformationFlip	TODO	TODO
TransformationFlipAndRotate90	TODO	TODO
TransformationMirror	TODO	TODO
TransformationMirrorAndRotate90	TODO	TODO
TransformationNone	TODO	TODO
TransformationRotate180	TODO	TODO
TransformationRotate270	TODO	TODO
TransformationRotate90	TODO	TODO

Methods¶

__init__(): Constructs a QImageIOHandler object.

canRead() → bool: TODO

currentImageNumber() → int

For image formats that support animation, this function returns the sequence number of the current image in the animation. If this function is called before any image is read(), -1 is returned. The number of the first image in the sequence is 0.

If the image format does not support animation, 0 is returned.