QImageIO

NAME

SYNOPSIS

Public Members

Static Public Members

DESCRIPTION

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 ()

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

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

QImageIO::~QImageIO ()

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

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.

The regexp is only applied on the first 14 bytes of the file.

Note that Qt assumes that there is only one handler per format; if two handlers support the same format, Qt will choose one arbitrarily. It is not possible to have one handler support reading, and another support writing.  

QString QImageIO::description () const

See also setDescription().  

QString QImageIO::fileName () const

See also setFileName().  

const char * QImageIO::format () const

float QImageIO::gamma () const

See also setGamma().  

const QImage & QImageIO::image () const

See also setImage().  

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

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

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]

QIODevice * QImageIO::ioDevice () const

See also setIODevice().  

QStrList QImageIO::outputFormats () [static]

Example: scribble/scribble.cpp.  

const char * QImageIO::parameters () const

See also setParameters().  

int QImageIO::quality () const

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

bool QImageIO::read ()

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 )

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

void QImageIO::setFileName ( const QString & fileName )

See also setIODevice().  

void QImageIO::setFormat ( const char * format )

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 )

The default value is 0.0.

See also gamma().  

void QImageIO::setIODevice ( QIODevice * ioDevice )

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 )

See also image().  

void QImageIO::setParameters ( const char * 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 )

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 )

See also status().  

int QImageIO::status () const

See also setStatus().  

bool QImageIO::write ()

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().

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