The QImage class provides a hardware-independent pixmap
representation with direct access to the pixel data.
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Detailed Description
The QImage class provides a hardware-independent pixmap
representation with direct access to the pixel data.
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
This enum type is used to describe the endianness of the CPU and
graphics hardware.
- 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
The functions scale() and smoothScale() use different modes for
scaling the image. The purpose of these modes is to retain the
ratio of the image if this is required.
- 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 ()
Constructs a null image.
See also isNull().
QImage::QImage ( int w, int h, int depth, int numColors = 0, Endian bitOrder = IgnoreEndian )
Constructs an image with w width, h height, depth bits
per pixel, numColors colors and bit order bitOrder.
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 )
Constructs an image with size size pixels, depth depth bits,
numColors and bitOrder endianness.
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 )
Constructs an image and tries to load the image from the file fileName.
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[] )
Constructs an image from xpm, which must be a valid XPM image.
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 )
Constructs an image from the binary data array. It tries to
guess the file format.
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 )
Constructs an image w pixels wide, h pixels high with a
color depth of depth, that uses an existing memory buffer, yourdata. The buffer must remain valid throughout the life of the
QImage. The image does not delete the buffer at destruction.
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 )
Constructs an image that uses an existing memory buffer. The
buffer must remain valid for the life of the QImage. The image
does not delete the buffer at destruction. The buffer is passed as
yourdata. The image's width is w and its height is h. The
color depth is depth. bpl specifies the number of bytes per
line.
If colortable is 0, a color table sufficient for numColors
will be allocated (and destructed later).
The endianness is specified by bitOrder.
QImage::QImage ( const QImage & image )
Constructs a shallow copy of image.
QImage::~QImage ()
Destroys the image and cleans up.
bool QImage::allGray () const
Returns TRUE if all the colors in the image are shades of gray
(i.e. their red, green and blue components are equal); otherwise
returns FALSE.
This function is slow for large 16-bit and 32-bit images.
See also isGrayscale().
Endian QImage::bitOrder () const
Returns the bit order for the image.
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
Returns a pointer to the first pixel data. This is equivalent to
scanLine(0).
See also numBytes(), scanLine(), and jumpTable().
Example: opengl/texture/gltexobj.cpp.
int QImage::bytesPerLine () const
Returns the number of bytes per image scanline. This is equivalent
to numBytes()/height().
See also numBytes() and scanLine().
QRgb QImage::color ( int i ) const
Returns the color in the color table at index i. The first
color is at index 0.
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
Returns a pointer to the color table.
See also numColors().
QImage QImage::convertBitOrder ( Endian bitOrder ) const
Converts the bit order of the image to bitOrder and returns the
converted image. The original image is not changed.
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
Converts the depth (bpp) of the image to depth and returns the
converted image. The original image is not changed.
The depth argument must be 1, 8, 16 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
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
QImage QImage::convertDepthWithPalette ( int d, QRgb * palette, int palette_count, int conversion_flags = 0 ) const
Returns an image with depth d, using the palette_count
colors pointed to by palette. If d is 1 or 8, the returned
image will have its color table ordered the same as palette.
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
Returns a deep copy of the image.
See also detach().
QImage QImage::copy ( int x, int y, int w, int h, int conversion_flags = 0 ) const
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
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
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
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 )
Sets the image width, height, depth, its number of colors
(in numColors), and bit order. Returns TRUE if successful, or
FALSE if the parameters are incorrect or if memory cannot be
allocated.
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 )
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
QImage QImage::createAlphaMask ( int conversion_flags = 0 ) const
Builds and returns a 1-bpp mask from the alpha buffer in this
image. Returns a null image if alpha buffer mode is disabled.
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
Creates and returns a 1-bpp heuristic mask for this image. It
works by selecting a color from one of the corners, then chipping
away pixels of that color starting at all the edges.
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
Returns the depth of the image.
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 and 32.
See also convertDepth().
void QImage::detach ()
Detaches from shared image data and makes sure that this image is
the only one referring to the data.
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
Returns the number of pixels that fit horizontally in a physical
meter. This and dotsPerMeterY() define the intended scale and
aspect ratio of the image.
See also setDotsPerMeterX().
int QImage::dotsPerMeterY () const
Returns the number of pixels that fit vertically in a physical
meter. This and dotsPerMeterX() define the intended scale and
aspect ratio of the image.
See also setDotsPerMeterY().
void QImage::fill ( uint pixel )
Fills the entire image with the pixel value 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]
Convenience function. Gets the data associated with the absolute
name abs_name from the default mime source factory and decodes it
to an image.
See also QMimeSourceFactory, QImage::fromMimeSource(), and QImageDrag::decode().
bool QImage::hasAlphaBuffer () const
Returns TRUE if alpha buffer mode is enabled; otherwise returns
FALSE.
See also setAlphaBuffer().
int QImage::height () const
Returns the height of the image.
See also width(), size(), and rect().
Examples: canvas/canvas.cpp and opengl/texture/gltexobj.cpp.
const char * QImage::imageFormat ( const QString & fileName ) [static]
Returns a string that specifies the image format of the file fileName, or 0 if the file cannot be read or if the format is not
recognized.
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]
Returns a list of image formats that are supported for image
input.
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]
Returns a list of image formats that are supported for image
input.
See also outputFormats(), inputFormatList(), and QImageIO.
void QImage::invertPixels ( bool invertAlpha = TRUE )
Inverts all pixel values in the image.
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 16-bit and 32-bit images, this function is equivalent to
allGray().
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
Returns TRUE if it is a null image; otherwise returns FALSE.
A null image has all parameters set to zero and no allocated data.
Example: showimg/showimg.cpp.
uchar ** QImage::jumpTable () const
Returns a pointer to the scanline pointer table.
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 )
Loads an image from the file fileName. Returns TRUE if the
image was successfully loaded; otherwise returns FALSE.
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 )
Loads an image from the first len bytes of binary data in buf. Returns TRUE if the image was successfully loaded; otherwise
returns FALSE.
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 )
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Loads an image from the QByteArray buf.
QImage QImage::mirror () const
Returns a QImage which is a vertically mirrored copy of this
image. The original QImage is not changed.
QImage QImage::mirror ( bool horizontal, bool vertical ) const
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
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
Returns the number of bytes occupied by the image data.
See also bytesPerLine() and bits().
int QImage::numColors () const
Returns the size of the color table for the image.
Notice that numColors() returns 0 for 16-bpp 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
Returns the number of pixels by which the image is intended to be
offset by when positioning relative to other images.
bool QImage::operator!= ( const QImage & i ) const
Returns TRUE if this image and image i have different contents;
otherwise returns FALSE. The comparison can be slow, unless there
is some obvious difference, such as different widths, in which
case the function will return quickly.
See also operator=().
QImage & QImage::operator= ( const QImage & image )
Assigns a shallow copy of image to
this image and returns a reference to this image.
See also copy().
QImage & QImage::operator= ( const QPixmap & pixmap )
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
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
Returns TRUE if this image and image i have the same contents;
otherwise returns FALSE. The comparison can be slow, unless there
is some obvious difference, such as different widths, in which
case the function will return quickly.
See also operator=().
QStringList QImage::outputFormatList () [static]
Returns a list of image formats that are supported for image
output.
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]
Returns a list of image formats that are supported for image
output.
See also inputFormats(), outputFormatList(), and QImageIO.
Example: showimg/showimg.cpp.
QRgb QImage::pixel ( int x, int y ) const
Returns the color of the pixel at the coordinates (x, y).
If (x, y) is not on the image, the
results are undefined.
See also setPixel(), qRed(), qGreen(), qBlue(), and valid().
Examples: canvas/canvas.cpp and qmag/qmag.cpp.
int QImage::pixelIndex ( int x, int y ) const
Returns the pixel index at the given coordinates.
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
Returns the enclosing rectangle (0, 0, width(), height()) of the
image.
See also width(), height(), and size().
void QImage::reset ()
Resets all image parameters and deallocates the image data.
bool QImage::save ( const QString & fileName, const char * format, int quality = -1 ) const
Saves the image to the file fileName, using the image file
format format and a quality factor of quality. quality
must be in the range 0..100 or -1. Specify 0 to obtain small
compressed files, 100 for large uncompressed files, and -1 (the
default) to use the default settings.
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 is an overloaded member function, provided for convenience. It behaves essentially like the above function.
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
Returns a copy of the image scaled to a rectangle of width w
and height h according to the ScaleMode mode.
- 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
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
The requested size of the image is s.
QImage QImage::scaleHeight ( int h ) const
Returns a scaled copy of the image. The returned image has a
height of h pixels. This function automatically calculates the
width of the image so that the ratio of the image is preserved.
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
Returns a scaled copy of the image. The returned image has a width
of w pixels. This function automatically calculates the height
of the image so that the ratio of the image is preserved.
If w is 0 or negative a null image is
returned.
See also scale(), scaleHeight(), smoothScale(), and xForm().
uchar * QImage::scanLine ( int i ) const
Returns a pointer to the pixel data at the scanline with index i. The first scanline is at index 0.
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.
See also bytesPerLine(), bits(), and jumpTable().
Example: desktop/desktop.cpp.
void QImage::setAlphaBuffer ( bool enable )
Enables alpha buffer mode if enable is TRUE, otherwise disables
it. The default setting is disabled.
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 )
Sets a color in the color table at index i to 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: desktop/desktop.cpp and themes/wood.cpp.
void QImage::setDotsPerMeterX ( int x )
Sets the value returned by dotsPerMeterX() to x.
void QImage::setDotsPerMeterY ( int y )
Sets the value returned by dotsPerMeterY() to y.
void QImage::setNumColors ( int numColors )
Resizes the color table to numColors colors.
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 )
Sets the value returned by offset() to p.
void QImage::setPixel ( int x, int y, uint index_or_rgb )
Sets the pixel index or color at the coordinates (x, y) to
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 )
Records string s for the keyword key. The key should be
a portable keyword recognizable by other software - some suggested
values can be found in
the PNG specification. s can be any text. lang should
specify the language code (see
RFC 1766) or 0.
QSize QImage::size () const
Returns the size of the image, i.e. its width and height.
See also width(), height(), and rect().
QImage QImage::smoothScale ( int w, int h, ScaleMode mode = ScaleFree ) const
Returns a smoothly scaled copy of the image. The returned image
has a size of width w by height h pixels if mode is ScaleFree. The modes ScaleMin and ScaleMax may be used to
preserve the ratio of the image: if mode is ScaleMin, the
returned image is guaranteed to fit into the rectangle specified
by w and h (it is as large as possible within the
constraints); if mode is ScaleMax, the returned image fits
at least into the specified rectangle (it is a small as possible
within the constraints).
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
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
The requested size of the image is s.
QImage QImage::swapRGB () const
Returns a QImage in which the values of the red and blue
components of all pixels have been swapped, effectively converting
an RGB image to a BGR image. The original QImage is not changed.
Endian QImage::systemBitOrder () [static]
Determines the bit order of the display hardware. Returns
QImage::LittleEndian (LSB first) or QImage::BigEndian (MSB first).
See also systemByteOrder().
Endian QImage::systemByteOrder () [static]
Determines the host computer byte order. Returns
QImage::LittleEndian (LSB first) or QImage::BigEndian (MSB first).
See also systemBitOrder().
QString QImage::text ( const char * key, const char * lang = 0 ) const
Returns the string recorded for the keyword key in language lang, or in a default language if lang is 0.
QString QImage::text ( const QImageTextKeyLang & kl ) const
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
Returns the string recorded for the keyword and language kl.
QStringList QImage::textKeys () const
Returns the keywords for which some texts are recorded.
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
Returns the language identifiers for which some texts are
recorded.
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
Returns a list of QImageTextKeyLang objects that enumerate all the
texts key/language pairs set by setText() for this image.
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
Returns TRUE if ( x, y ) is a valid coordinate in the image;
otherwise returns FALSE.
See also width(), height(), and pixelIndex().
Examples: canvas/canvas.cpp and qmag/qmag.cpp.
int QImage::width () const
Returns the width of the image.
See also height(), size(), and rect().
Examples: canvas/canvas.cpp and opengl/texture/gltexobj.cpp.
QImage QImage::xForm ( const QWMatrix & matrix ) const
Returns a copy of the image that is transformed using the
transformation matrix, matrix.
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 Functions
Writes the image image to the stream s as a PNG image, or as a
BMP image if the stream's version is 1.
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.
Reads an image from the stream s and stores it in image.
See also QImage::load() and Format of the QDataStream operators.
This file is part of the Qt toolkit.
Copyright © 1995-2003
Trolltech. All Rights Reserved.
