QImage

NAME

SYNOPSIS

Public Members

Static Public Members

RELATED FUNCTION DOCUMENTATION

DESCRIPTION

It is one of the two classes Qt provides for dealing with images, the other being QPixmap. QImage is designed and optimized for I/O and for direct pixel access/manipulation. QPixmap is designed and optimized for drawing. There are (slow) functions to convert between QImage and QPixmap: QPixmap::convertToImage() and QPixmap::convertFromImage().

An image has the parameters width, height and depth (bits per pixel, bpp), a color table and the actual pixels. QImage supports 1-bpp, 8-bpp and 32-bpp image data. 1-bpp and 8-bpp images use a color lookup table; the pixel value is a color table index.

32-bpp images encode an RGB value in 24 bits and ignore the color table. The most significant byte is used for the alpha buffer.

An entry in the color table is an RGB triplet encoded as a uint. Use the qRed(), qGreen() and qBlue() functions (qcolor.h) to access the components, and qRgb to make an RGB triplet (see the QColor class documentation).

1-bpp (monochrome) images have a color table with a most two colors. There are two different formats: big endian (MSB first) or little endian (LSB first) bit order. To access a single bit you will must do some bit shifts:

    QImage image;


    // sets bit at (x,y) to 1


    if ( image.bitOrder() == QImage::LittleEndian )


        *(image.scanLine(y) + (x >> 3)) |= 1 << (x & 7);


    else


        *(image.scanLine(y) + (x >> 3)) |= 1 << (7 - (x & 7));

If this looks complicated, it might be a good idea to convert the 1-bpp image to an 8-bpp image using convertDepth().

8-bpp images are much easier to work with than 1-bpp images because they have a single byte per pixel:

    QImage image;


    // set entry 19 in the color table to yellow


    image.setColor( 19, qRgb(255,255,0) );


    // set 8 bit pixel at (x,y) to value yellow (in color table)


    *(image.scanLine(y) + x) = 19;

32-bpp images ignore the color table; instead, each pixel contains the RGB triplet. 24 bits contain the RGB value; the most significant byte is reserved for the alpha buffer.

    QImage image;


    // sets 32 bit pixel at (x,y) to yellow.


    uint *p = (uint *)image.scanLine(y) + x;


    *p = qRgb(255,255,0);

On Qt/Embedded, scanlines are aligned to the pixel depth and may be padded to any degree, while on all other platforms, the scanlines are 32-bit aligned for all depths. The constructor taking a uchar* argument always expects 32-bit aligned data. On Qt/Embedded, an additional constructor allows the number of bytes-per-line to be specified.

QImage supports a variety of methods for getting information about the image, for example, colorTable(), allGray(), isGrayscale(), bitOrder(), bytesPerLine(), depth(), dotsPerMeterX() and dotsPerMeterY(), hasAlphaBuffer(), numBytes(), numColors(), and width() and height().

Pixel colors are retrieved with pixel() and set with setPixel().

QImage also supports a number of functions for creating a new image that is a transformed version of the original. For example, copy(), convertBitOrder(), convertDepth(), createAlphaMask(), createHeuristicMask(), mirror(), scale(), smoothScale(), swapRGB() and xForm(). There are also functions for changing attributes of an image in-place, for example, setAlphaBuffer(), setColor(), setDotsPerMeterX() and setDotsPerMeterY() and setNumColors().

Images can be loaded and saved in the supported formats. Images are saved to a file with save(). Images are loaded from a file with load() (or in the constructor) or from an array of data with loadFromData(). The lists of supported formats are available from inputFormatList() and outputFormatList().

Strings of text may be added to images using setText().

The QImage class uses explicit sharing, similar to that used by QMemArray.

New image formats can be added as plugins.

See also QImageIO, QPixmap, Shared Classes, Graphics Classes, Image Processing Classes, and Implicitly and Explicitly Shared Classes.  

Member Type Documentation

QImage::Endian

QImage::IgnoreEndian - Endianness does not matter. Useful for some operations that are independent of endianness.

QImage::BigEndian - Network byte order, as on SPARC and Motorola CPUs.

QImage::LittleEndian - PC/Alpha byte order.

QImage::ScaleMode

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QImage::ScaleFree - The image is scaled freely: the resulting image fits exactly into the specified size; the ratio will not necessarily be preserved.

QImage::ScaleMin - The ratio of the image is preserved and the resulting image is guaranteed to fit into the specified size (it is as large as possible within these constraints) - the image might be smaller than the requested size.

QImage::ScaleMax - The ratio of the image is preserved and the resulting image fills the whole specified rectangle (it is as small as possible within these constraints) - the image might be larger than the requested size.

MEMBER FUNCTION DOCUMENTATION

QImage::QImage ()

See also isNull().  

QImage::QImage ( int w, int h, int depth, int numColors = 0, Endian bitOrder = IgnoreEndian )

Using this constructor is the same as first constructing a null image and then calling the create() function.

See also create().  

QImage::QImage ( const QSize & size, int depth, int numColors = 0, Endian bitOrder = IgnoreEndian )

Using this constructor is the same as first constructing a null image and then calling the create() function.

See also create().  

QImage::QImage ( const QString & fileName, const char * format = 0 )

If format is specified, the loader attempts to read the image using the specified format. If format is not specified (which is the default), the loader reads a few bytes from the header to guess the file format.

If the loading of the image failed, this object is a null image.

The QImageIO documentation lists the supported image formats and explains how to add extra formats.

See also load(), isNull(), and QImageIO.  

QImage::QImage ( const char * const xpm[] )

Errors are silently ignored.

Note that it's possible to squeeze the XPM variable a little bit by using an unusual declaration:

        static const char * const start_xpm[]={


            "16 15 8 1",


            "a c #cec6bd",


        ....

The extra const makes the entire definition read-only, which is slightly more efficient (e.g. when the code is in a shared library) and ROMable when the application is to be stored in ROM.  

QImage::QImage ( const QByteArray & array )

If the loading of the image failed, this object is a null image.

See also loadFromData(), isNull(), and imageFormat().  

QImage::QImage ( uchar * yourdata, int w, int h, int depth, QRgb * colortable, int numColors, Endian bitOrder )

If colortable is 0, a color table sufficient for numColors will be allocated (and destructed later).

Note that yourdata must be 32-bit aligned.

The endianness is given in bitOrder.  

QImage::QImage ( uchar * yourdata, int w, int h, int depth, int bpl, QRgb * colortable, int numColors, Endian bitOrder )

If colortable is 0, a color table sufficient for numColors will be allocated (and destructed later).

The endianness is specified by bitOrder.

Warning: This constructor is only available on Qt/Embedded.  

QImage::QImage ( const QImage & image )

QImage::~QImage ()

bool QImage::allGray () const

This function is slow for large 16-bit (Qt/Embedded only) and 32-bit images.

See also isGrayscale().  

Endian QImage::bitOrder () const

If it is a 1-bpp image, this function returns either QImage::BigEndian or QImage::LittleEndian.

If it is not a 1-bpp image, this function returns QImage::IgnoreEndian.

See also depth().  

uchar * QImage::bits () const

See also numBytes(), scanLine(), and jumpTable().

Example: opengl/texture/gltexobj.cpp.  

int QImage::bytesPerLine () const

See also numBytes() and scanLine().  

QRgb QImage::color ( int i ) const

A color value is an RGB triplet. Use the qRed(), qGreen() and qBlue() functions (defined in qcolor.h) to get the color value components.

See also setColor(), numColors(), and QColor.

Example: themes/wood.cpp.  

QRgb * QImage::colorTable () const

See also numColors().  

QImage QImage::convertBitOrder ( Endian bitOrder ) const

Returns *this if the bitOrder is equal to the image bit order, or a null image if this image cannot be converted.

See also bitOrder(), systemBitOrder(), and isNull().  

QImage QImage::convertDepth ( int depth, int conversion_flags ) const

The depth argument must be 1, 8, 16 (Qt/Embedded only) or 32.

Returns *this if depth is equal to the image depth, or a null image if this image cannot be converted.

If the image needs to be modified to fit in a lower-resolution result (e.g. converting from 32-bit to 8-bit), use the conversion_flags to specify how you'd prefer this to happen.

See also Qt::ImageConversionFlags, depth(), and isNull().  

QImage QImage::convertDepth ( int depth ) const

QImage QImage::convertDepthWithPalette ( int d, QRgb * palette, int palette_count, int conversion_flags = 0 ) const

If the image needs to be modified to fit in a lower-resolution result (e.g. converting from 32-bit to 8-bit), use the conversion_flags to specify how you'd prefer this to happen.

Note: currently no closest-color search is made. If colors are found that are not in the palette, the palette may not be used at all. This result should not be considered valid because it may change in future implementations.

Currently inefficient for non-32-bit images.

See also Qt::ImageConversionFlags.  

QImage QImage::copy () const

See also detach().  

QImage QImage::copy ( int x, int y, int w, int h, int conversion_flags = 0 ) const

Returns a deep copy of a sub-area of the image.

The returned image is always w by h pixels in size, and is copied from position x, y in this image. In areas beyond this image pixels are filled with pixel 0.

If the image needs to be modified to fit in a lower-resolution result (e.g. converting from 32-bit to 8-bit), use the conversion_flags to specify how you'd prefer this to happen.

See also bitBlt() and Qt::ImageConversionFlags.  

QImage QImage::copy ( const QRect & r ) const

Returns a deep copy of a sub-area of the image.

The returned image always has the size of the rectangle r. In areas beyond this image pixels are filled with pixel 0.  

bool QImage::create ( int width, int height, int depth, int numColors = 0, Endian bitOrder = IgnoreEndian )

The width and height is limited to 32767. depth must be 1, 8, or 32. If depth is 1, bitOrder must be set to either QImage::LittleEndian or QImage::BigEndian. For other depths bitOrder must be QImage::IgnoreEndian.

This function allocates a color table and a buffer for the image data. The image data is not initialized.

The image buffer is allocated as a single block that consists of a table of scanline pointers (jumpTable()) and the image data (bits()).

See also fill(), width(), height(), depth(), numColors(), bitOrder(), jumpTable(), scanLine(), bits(), bytesPerLine(), and numBytes().  

bool QImage::create ( const QSize &, int depth, int numColors = 0, Endian bitOrder = IgnoreEndian )

QImage QImage::createAlphaMask ( int conversion_flags = 0 ) const

See QPixmap::convertFromImage() for a description of the conversion_flags argument.

The returned image has little-endian bit order, which you can convert to big-endianness using convertBitOrder().

See also createHeuristicMask(), hasAlphaBuffer(), and setAlphaBuffer().  

QImage QImage::createHeuristicMask ( bool clipTight = TRUE ) const

The four corners vote for which color is to be masked away. In case of a draw (this generally means that this function is not applicable to the image), the result is arbitrary.

The returned image has little-endian bit order, which you can convert to big-endianness using convertBitOrder().

If clipTight is TRUE the mask is just large enough to cover the pixels; otherwise, the mask is larger than the data pixels.

This function disregards the alpha buffer.

See also createAlphaMask().  

int QImage::depth () const

The image depth is the number of bits used to encode a single pixel, also called bits per pixel (bpp) or bit planes of an image.

The supported depths are 1, 8, 16 (Qt/Embedded only) and 32.

See also convertDepth().  

void QImage::detach ()

If multiple images share common data, this image makes a copy of the data and detaches itself from the sharing mechanism. Nothing is done if there is just a single reference.

See also copy().

Example: themes/wood.cpp.  

int QImage::dotsPerMeterX () const

See also setDotsPerMeterX().  

int QImage::dotsPerMeterY () const

See also setDotsPerMeterY().  

void QImage::fill ( uint pixel )

If the depth of this image is 1, only the lowest bit is used. If you say fill(0), fill(2), etc., the image is filled with 0s. If you say fill(1), fill(3), etc., the image is filled with 1s. If the depth is 8, the lowest 8 bits are used.

If the depth is 32 and the image has no alpha buffer, the pixel value is written to each pixel in the image. If the image has an alpha buffer, only the 24 RGB bits are set and the upper 8 bits (alpha value) are left unchanged.

Note: QImage::pixel() returns the color of the pixel at the given coordinates; QColor::pixel() returns the pixel value of the underlying window system (essentially an index value), so normally you will want to use QImage::pixel() to use a color from an existing image or QColor::rgb() to use a specific color.

See also invertPixels(), depth(), hasAlphaBuffer(), and create().  

QImage QImage::fromMimeSource ( const QString & abs_name ) [static]

See also QMimeSourceFactory, QImage::fromMimeSource(), and QImageDrag::decode().  

bool QImage::hasAlphaBuffer () const

See also setAlphaBuffer().  

int QImage::height () const

See also width(), size(), and rect().

Examples:  

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

The QImageIO documentation lists the guaranteed supported image formats, or use QImage::inputFormats() and QImage::outputFormats() to get lists that include the installed formats.

See also load() and save().  

QStringList QImage::inputFormatList () [static]

Note that if you want to iterate over the list, you should iterate over a copy, e.g.

    QStringList list = myImage.inputFormatList();


    QStringList::Iterator it = list.begin();


    while( it != list.end() ) {


        myProcessing( *it );


        ++it;


    }

See also outputFormatList(), inputFormats(), and QImageIO.

Example: showimg/showimg.cpp.  

QStrList QImage::inputFormats () [static]

See also outputFormats(), inputFormatList(), and QImageIO.  

void QImage::invertPixels ( bool invertAlpha = TRUE )

If the depth is 32: if invertAlpha is TRUE, the alpha bits are also inverted, otherwise they are left unchanged.

If the depth is not 32, the argument invertAlpha has no meaning.

Note that inverting an 8-bit image means to replace all pixels using color index i with a pixel using color index 255 minus i. Similarly for a 1-bit image. The color table is not changed.

See also fill(), depth(), and hasAlphaBuffer().  

bool QImage::isGrayscale () const

For 8-bpp images, this function returns TRUE if color(i) is QRgb(i,i,i) for all indices of the color table; otherwise returns FALSE.

See also allGray() and depth().  

bool QImage::isNull () const

A null image has all parameters set to zero and no allocated data.

Example: showimg/showimg.cpp.  

uchar ** QImage::jumpTable () const

This is the beginning of the data block for the image.

See also bits() and scanLine().  

bool QImage::load ( const QString & fileName, const char * format = 0 )

If format is specified, the loader attempts to read the image using the specified format. If format is not specified (which is the default), the loader reads a few bytes from the header to guess the file format.

The QImageIO documentation lists the supported image formats and explains how to add extra formats.

See also loadFromData(), save(), imageFormat(), QPixmap::load(), and QImageIO.  

bool QImage::loadFromData ( const uchar * buf, uint len, const char * format = 0 )

If format is specified, the loader attempts to read the image using the specified format. If format is not specified (which is the default), the loader reads a few bytes from the header to guess the file format.

The QImageIO documentation lists the supported image formats and explains how to add extra formats.

See also load(), save(), imageFormat(), QPixmap::loadFromData(), and QImageIO.  

bool QImage::loadFromData ( QByteArray buf, const char * format = 0 )

Loads an image from the QByteArray buf.  

QImage QImage::mirror () const

QImage QImage::mirror ( bool horizontal, bool vertical ) const

Returns a mirror of the image, mirrored in the horizontal and/or the vertical direction depending on whether horizontal and vertical are set to TRUE or FALSE. The original image is not changed.

See also smoothScale().  

int QImage::numBytes () const

See also bytesPerLine() and bits().  

int QImage::numColors () const

Notice that numColors() returns 0 for 16-bpp (Qt/Embedded only) and 32-bpp images because these images do not use color tables, but instead encode pixel values as RGB triplets.

See also setNumColors() and colorTable().

Example: themes/wood.cpp.  

QPoint QImage::offset () const

bool QImage::operator!= ( const QImage & i ) const

See also operator=().  

QImage & QImage::operator= ( const QImage & image )

See also copy().  

QImage & QImage::operator= ( const QPixmap & pixmap )

Sets the image bits to the pixmap contents and returns a reference to the image.

If the image shares data with other images, it will first dereference the shared data.

Makes a call to QPixmap::convertToImage().  

bool QImage::operator== ( const QImage & i ) const

See also operator=().  

QStringList QImage::outputFormatList () [static]

Note that if you want to iterate over the list, you should iterate over a copy, e.g.

    QStringList list = myImage.outputFormatList();


    QStringList::Iterator it = list.begin();


    while( it != list.end() ) {


        myProcessing( *it );


        ++it;


    }

See also inputFormatList(), outputFormats(), and QImageIO.  

QStrList QImage::outputFormats () [static]

See also inputFormats(), outputFormatList(), and QImageIO.

Example: showimg/showimg.cpp.  

QRgb QImage::pixel ( int x, int y ) const

If (x, y) is not on the image, the results are undefined.

See also setPixel(), qRed(), qGreen(), qBlue(), and valid().

Examples:  

int QImage::pixelIndex ( int x, int y ) const

If (x, y) is not valid, or if the image is not a paletted image (depth() > 8), the results are undefined.

See also valid() and depth().  

QRect QImage::rect () const

See also width(), height(), and size().  

void QImage::reset ()

bool QImage::save ( const QString & fileName, const char * format, int quality = -1 ) const

Returns TRUE if the image was successfully saved; otherwise returns FALSE.

See also load(), loadFromData(), imageFormat(), QPixmap::save(), and QImageIO.  

bool QImage::save ( QIODevice * device, const char * format, int quality = -1 ) const

This function writes a QImage to the QIODevice, device. This can be used, for example, to save an image directly into a QByteArray:

    QImage image;


    QByteArray ba;


    QBuffer buffer( ba );


    buffer.open( IO_WriteOnly );


    image.save( &buffer, "PNG" ); // writes image into ba in PNG format

QImage QImage::scale ( int w, int h, ScaleMode mode = ScaleFree ) const

If mode is ScaleFree, the image is scaled to (w, h).

If mode is ScaleMin, the image is scaled to a rectangle as large as possible inside (w, h), preserving the aspect ratio.

If mode is ScaleMax, the image is scaled to a rectangle as small as possible outside (w, h), preserving the aspect ratio.

If either the width w or the height h is 0 or negative, this function returns a null image.

This function uses a simple, fast algorithm. If you need better quality, use smoothScale() instead.

See also scaleWidth(), scaleHeight(), smoothScale(), and xForm().  

QImage QImage::scale ( const QSize & s, ScaleMode mode = ScaleFree ) const

The requested size of the image is s.  

QImage QImage::scaleHeight ( int h ) const

If h is 0 or negative a null image is returned.

See also scale(), scaleWidth(), smoothScale(), and xForm().

Example: table/small-table-demo/main.cpp.  

QImage QImage::scaleWidth ( int w ) const

If w is 0 or negative a null image is returned.

See also scale(), scaleHeight(), smoothScale(), and xForm().  

uchar * QImage::scanLine ( int i ) const

The scanline data is aligned on a 32-bit boundary.

Warning: If you are accessing 32-bpp image data, cast the returned pointer to QRgb* (QRgb has a 32-bit size) and use it to read/write the pixel value. You cannot use the uchar* pointer directly, because the pixel format depends on the byte order on the underlying platform. Hint: use qRed(), qGreen() and qBlue(), etc. (qcolor.h) to access the pixels.

Warning: If you are accessing 16-bpp image data, you must handle endianness yourself. (Qt/Embedded only)

See also bytesPerLine(), bits(), and jumpTable().

Example: desktop/desktop.cpp.  

void QImage::setAlphaBuffer ( bool enable )

An 8-bpp image has 8-bit pixels. A pixel is an index into the color table, which contains 32-bit color values. In a 32-bpp image, the 32-bit pixels are the color values.

This 32-bit value is encoded as follows: The lower 24 bits are used for the red, green, and blue components. The upper 8 bits contain the alpha component.

The alpha component specifies the transparency of a pixel. 0 means completely transparent and 255 means opaque. The alpha component is ignored if you do not enable alpha buffer mode.

The alpha buffer is used to set a mask when a QImage is translated to a QPixmap.

See also hasAlphaBuffer() and createAlphaMask().  

void QImage::setColor ( int i, QRgb c )

A color value is an RGB triplet. Use the qRgb() function (defined in qcolor.h) to make RGB triplets.

See also color(), setNumColors(), and numColors().

Examples:  

void QImage::setDotsPerMeterX ( int x )

void QImage::setDotsPerMeterY ( int y )

void QImage::setNumColors ( int numColors )

If the color table is expanded all the extra colors will be set to black (RGB 0,0,0).

See also numColors(), color(), setColor(), and colorTable().  

void QImage::setOffset ( const QPoint & p )

void QImage::setPixel ( int x, int y, uint index_or_rgb )

If (x, y) is not valid, the result is undefined.

If the image is a paletted image (depth() <= 8) and index_or_rgb >= numColors(), the result is undefined.

See also pixelIndex(), pixel(), qRgb(), qRgba(), and valid().  

void QImage::setText ( const char * key, const char * lang, const QString & s )

QSize QImage::size () const

See also width(), height(), and rect().  

QImage QImage::smoothScale ( int w, int h, ScaleMode mode = ScaleFree ) const

For 32-bpp images and 1-bpp/8-bpp color images the result will be 32-bpp, whereas all-gray images (including black-and-white 1-bpp) will produce 8-bit grayscale images with the palette spanning 256 grays from black to white.

This function uses code based on pnmscale.c by Jef Poskanzer.

pnmscale.c - read a portable anymap and scale it

Copyright (C) 1989, 1991 by Jef Poskanzer.

Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation. This software is provided "as is" without express or implied warranty.

See also scale() and mirror().  

QImage QImage::smoothScale ( const QSize & s, ScaleMode mode = ScaleFree ) const

The requested size of the image is s.  

QImage QImage::swapRGB () const

Endian QImage::systemBitOrder () [static]

See also systemByteOrder().  

Endian QImage::systemByteOrder () [static]

See also systemBitOrder().  

QString QImage::text ( const char * key, const char * lang = 0 ) const

QString QImage::text ( const QImageTextKeyLang & kl ) const

Returns the string recorded for the keyword and language kl.  

QStringList QImage::textKeys () const

Note that if you want to iterate over the list, you should iterate over a copy, e.g.

    QStringList list = myImage.textKeys();


    QStringList::Iterator it = list.begin();


    while( it != list.end() ) {


        myProcessing( *it );


        ++it;


    }

See also textList(), text(), setText(), and textLanguages().  

QStringList QImage::textLanguages () const

Note that if you want to iterate over the list, you should iterate over a copy, e.g.

    QStringList list = myImage.textLanguages();


    QStringList::Iterator it = list.begin();


    while( it != list.end() ) {


        myProcessing( *it );


        ++it;


    }

See also textList(), text(), setText(), and textKeys().  

QValueList<QImageTextKeyLang> QImage::textList () const

Note that if you want to iterate over the list, you should iterate over a copy, e.g.

    QValueList<QImageTextKeyLang> list = myImage.textList();


    QValueList<QImageTextKeyLang>::Iterator it = list.begin();


    while( it != list.end() ) {


        myProcessing( *it );


        ++it;


    }

bool QImage::valid ( int x, int y ) const

See also width(), height(), and pixelIndex().

Examples:  

int QImage::width () const

See also height(), size(), and rect().

Examples:  

QImage QImage::xForm ( const QWMatrix & matrix ) const

The transformation matrix is internally adjusted to compensate for unwanted translation, i.e. xForm() returns the smallest image that contains all the transformed points of the original image.

See also scale(), QPixmap::xForm(), QPixmap::trueMatrix(), and QWMatrix.  

RELATED FUNCTION DOCUMENTATION

void bitBlt ( QImage * dst, int dx, int dy, const QImage * src, int sx, int sy, int sw, int sh, int conversion_flags )

sx, sy is the top-left pixel in src, dx, dy is the top-left position in dst and sw, \sh is the size of the copied block.

The copying is clipped if areas outside src or dst are specified.

If sw is -1, it is adjusted to src->width(). Similarly, if sh is -1, it is adjusted to src->height().

Currently inefficient for non 32-bit images.  

QDataStream & operator<< ( QDataStream & s, const QImage & image )

Note that writing the stream to a file will not produce a valid image file.

See also QImage::save() and Format of the QDataStream operators.  

QDataStream & operator>> ( QDataStream & s, QImage & image )

See also QImage::load() and Format of the QDataStream operators.

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