QImageIO Class

Qt 3.0.5

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QImageIO Class Reference

The QImageIO class contains parameters for loading and saving images. More...

#include <qimage.h>

List of all member functions.

Public Members

Static Public Members

Detailed Description

The QImageIO class contains parameters for loading and saving images.

QImageIO contains a QIODevice object that is used for image data I/O. The programmer can install new image file formats in addition to those that Qt provides.

Qt currently supports the following image file formats: PNG, BMP, XBM, XPM and PNM. It may also support JPEG, MNG and GIF, if specially configured during compilation. The different PNM formats are: PBM (P1 or P4), PGM (P2 or P5), and PPM (P3 or P6).

You don't normally need to use this class; QPixmap::load(), QPixmap::save(), and QImage contain sufficient functionality.

For image files that contain sequences of images, only the first is read. See QMovie for loading multiple images.

PBM, PGM, and PPM format output is always in the more condensed raw format. PPM and PGM files with more than 256 levels of intensity are scaled down when reading.

Warning: If you are in a country which recognizes software patents and in which Unisys holds a patent on LZW compression and/or decompression and you want to use GIF, Unisys may require you to license the technology. Such countries include Canada, Japan, the USA, France, Germany, Italy and the UK.

GIF support may be removed completely in a future version of Qt. We recommend using the PNG format.

See also QImage, QPixmap, QFile, QMovie, Graphics Classes, Image Processing Classes and Input/Output and Networking.

Member Function Documentation

QImageIO::QImageIO ()

Constructs a QImageIO object with all parameters set to zero.

QImageIO::QImageIO ( QIODevice * ioDevice, const char * format )

Constructs a QImageIO object with the I/O device ioDevice and a format tag.

QImageIO::QImageIO ( const QString & fileName, const char * format )

Constructs a QImageIO object with the file name fileName and a format tag.

QImageIO::~QImageIO ()

Destroys the object and all related data.

void QImageIO::defineIOHandler ( const char * format, const char * header, const char * flags, image_io_handler readImage, image_io_handler writeImage ) [static]

Defines an image I/O handler for the image format called format, which is recognized using the regular expression header, read using readImage and written using writeImage.

flags is a string of single-character flags for this format. The only flag defined currently is T (upper case), so the only legal value for flags are "T" and the empty string. The "T" flag means that the image file is a text file, and Qt should treat all newline conventions as equivalent. (XPM files and some PPM files are text files for example.)

format is used to select a handler to write a QImage; header is used to select a handler to read an image file.

If readImage is a null pointer, the QImageIO will not be able to read images in format. If writeImage is a null pointer, the QImageIO will not be able to write images in format. If both are null, the QImageIO object is valid but useless.

Example: 

        void readGIF( QImageIO *image )
        {
        // read the image using the image->ioDevice()
        }

        void writeGIF( QImageIO *image )
        {
        // write the image using the image->ioDevice()
        }

        // add the GIF image handler

        QImageIO::defineIOHandler( "GIF",
                                   "^GIF[0-9][0-9][a-z]",
                                   0,
                                   readGIF,
                                   writeGIF );

Before the regex test, all the 0 bytes in the file header are converted to 1 bytes. This is done because when Qt was ASCII-based, QRegExp could not handle 0 bytes in strings.

(Note that if one handlerIO supports writing a format and another supports reading it, Qt supports both reading and writing. If two handlers support the same operation, Qt chooses one arbitrarily.)

QString QImageIO::description () const

Returns the image description string.

See also setDescription().

QString QImageIO::fileName () const

Returns the file name currently set.

See also setFileName().

const char * QImageIO::format () const

Returns the image format string or 0 if no format has been explicitly set.

float QImageIO::gamma () const

Returns the gamma value at which the image will be viewed.

See also setGamma().

const QImage & QImageIO::image () const

Returns the image currently set.

See also setImage().

const char * QImageIO::imageFormat ( const QString & fileName ) [static]

Returns a string that specifies the image format of the file fileName, or null if the file cannot be read or if the format is not recognized.

const char * QImageIO::imageFormat ( QIODevice * d ) [static]

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Returns a string that specifies the image format of the image read from IO device d, or 0 if the device cannot be read or if the format is not recognized.

Make sure that d is at the right position in the device (for example, at the beginning of the file).

See also QIODevice::at().

QStrList QImageIO::inputFormats () [static]

Returns a sorted list of image formats that are supported for image input.

QIODevice * QImageIO::ioDevice () const

Returns the IO device currently set.

See also setIODevice().

QStrList QImageIO::outputFormats () [static]

Returns a sorted list of image formats that are supported for image output.

Example: scribble/scribble.cpp.

const char * QImageIO::parameters () const

Returns the image's parameters string.

See also setParameters().

int QImageIO::quality () const

Returns the quality of the written image, related to the compression ratio.

See also setQuality() and QImage::save().

bool QImageIO::read ()

Reads an image into memory and returns TRUE if the image was successfully read; otherwise returns FALSE.

Before reading an image you must set an IO device or a file name. If both an IO device and a file name have been set, the IO device will be used.

Setting the image file format string is optional.

Note that this function does not set the format used to read the image. If you need that information, use the imageFormat() static functions.

Example: 

        QImageIO iio;
        QPixmap  pixmap;
        iio.setFileName( "vegeburger.bmp" );
        if ( image.read() )        // ok
            pixmap = iio.image();  // convert to pixmap

See also setIODevice(), setFileName(), setFormat(), write() and QPixmap::load().

void QImageIO::setDescription ( const QString & description )

Sets the image description string for image handlers that support image descriptions to description.

Currently, no image format supported by Qt uses the description string.

void QImageIO::setFileName ( const QString & fileName )

Sets the name of the file to read or write an image from to fileName.

See also setIODevice().

void QImageIO::setFormat ( const char * format )

Sets the image format to format for the image to be read or written.

It is necessary to specify a format before writing an image, but it is not necessary to specify a format before reading an image.

If no format has been set, Qt guesses the image format before reading it. If a format is set the image will only be read if it has that format.

See also read(), write() and format().

void QImageIO::setGamma ( float gamma )

Sets the gamma value at which the image will be viewed to gamma. If the image format stores a gamma value for which the image is intended to be used, then this setting will be used to modify the image. Setting to 0.0 will disable gamma correction (i.e. any specification in the file will be ignored).

The default value is 0.0.

See also gamma().

void QImageIO::setIODevice ( QIODevice * ioDevice )

Sets the IO device to be used for reading or writing an image.

Setting the IO device allows images to be read/written to any block-oriented QIODevice.

If ioDevice is not null, this IO device will override file name settings.

See also setFileName().

void QImageIO::setImage ( const QImage & image )

Sets the image to image.

See also image().

void QImageIO::setParameters ( const char * parameters )

Sets the image's parameter string to parameters. This is for image handlers that require special parameters.

Although the current image formats supported by Qt ignore the parameters string, it may be used in future extensions or by contributions (for example, JPEG).

See also parameters().

void QImageIO::setQuality ( int q )

Sets the quality of the written image to q, related to the compression ratio.

q must be in the range -1..100. Specify 0 to obtain small compressed files, 100 for large uncompressed files. (-1 signifies the default compression.)

See also quality() and QImage::save().

void QImageIO::setStatus ( int status )

Sets the image IO status to status. A non-zero value indicates an error, whereas 0 means that the IO operation was successful.

See also status().

int QImageIO::status () const

Returns the image's IO status. A non-zero value indicates an error, whereas 0 means that the IO operation was successful.

See also setStatus().

bool QImageIO::write ()

Writes an image to an IO device and returns TRUE if the image was successfully written; otherwise returns FALSE.

Before writing an image you must set an IO device or a file name. If both an IO device and a file name have been set, the IO device will be used.

The image will be written using the specified image format.

Example: 

        QImageIO iio;
        QImage   im;
        im = pixmap; // convert to image
        iio.setImage( im );
        iio.setFileName( "vegeburger.bmp" );
        iio.setFormat( "BMP" );
        if ( iio.write() )
            // returned TRUE if written successfully

See also setIODevice(), setFileName(), setFormat(), read() and QPixmap::save().

This file is part of the Qt toolkit. Copyright © 1995-2002 Trolltech. All Rights Reserved.

Copyright © 2002 TrolltechTrademarks
Qt version 3.0.5

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