The QImage class provides a hardware-independent pixmap representation with direct access to the pixel data. More...
#include <qimage.h>
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 QPixmp; 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 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 maximum 2 colors. There are two different formats; big endian (MSB first) or little endian (LSB first) bit order. To access a single bit, you will have to do some bitshifts:
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 and 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);
The scanlines are 32-bit aligned for all depths.
The QImage class uses explicit sharing, similar to that of QArray and QString.
See also: QImageIO, QPixmap and Shared Classes
Examples: qtimage/qtimage.cpp desktop/desktop.cpp qmag/qmag.cpp
Constructs a null image.
See also: isNull().
Constructs a shallow copy of image.
Constructs an image from loading fileName and an optional format.
See also: load().
Constructs an image from xpm, which must be a valid XPM image.
Errors are silently ignored.
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().
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
Destroys the image and cleans up.
Returns TRUE if all the colors in the image are shades of gray, that is their R, G, and B components are equal. This function is slow for large 32-bit images.
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().
Returns a pointer to the first pixel data. Equivalent to scanLine(0).
See also: scanLine().
Returns the number of bytes per image scanline. This is equivalent to numBytes()/height().
Returns the color in the color table at index i.
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() and QColor.
Returns a pointer to the color table.
Converts the bit order of the image to bitOrder and returns the converted image.
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() and setBitOrder().
Converts the depth (bpp) of the image to depth and returns the converted image. The original image is left undisturbed.
The depth argument must be 1, 8 or 32.
See QPixmap::convertFromImage for a description of the conversion_flags argument.
Returns *this if depth is equal to the image depth, or a null
image if this image cannot be converted.
See also: depth() and isNull().
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
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, as it may change in future implementations.
Currently inefficient for non 32-bit images.
Returns a deep copy of the image.
Returns a deep copy of a sub-area of the image.
See also: bitBlt().
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
Sets the image width, height, depth, number of colors 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, then 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: width(), height(), depth(), numColors(), bitOrder(), jumpTable(), scanLine(), bits(), bytesPerLine() and numBytes().
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
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().
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 over 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 voting results are undocumented.
The returned image has little-endian bit order, which you can convert to big-endianness using convertBitOrder().
This function disregards the alpha buffer.
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 and 32.
Detaches from shared image data and makes sure that this image is the only one referring 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.
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.
Returns TRUE if alpha buffer mode is enabled, otherwise FALSE.
See also: setAlphaBuffer().
Returns the height of the image.
See also: width(), size() and rect().
[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 cannot be recognized.
The QImageIO documentation lists the guaranteed supported image formats, or use the QImage::inputFormats() QImage::outputFormats() to get lists that include installed formats.
[static]Returns a list of image formats which are supported for image input.
Returns TRUE if the image is allGray(), and if the image is 32-bpp or a 256-color 8-bpp image for which color(i) is QRgb(i,i,i).
Returns TRUE if it is a null image.
A null image has all parameters set to zero and no allocated data.
Examples: qtimage/qtimage.cpp
Returns a pointer to the scanline pointer table.
This is the beginning of the data block for the image.
Loads an image from the file fileName. Returns TRUE if successful, or FALSE if the image could not be loaded.
If format is specified, the loader attempts to read the image using the specified format. If format is not specified (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.
Loads an image from the binary data in buf (len bytes). Returns TRUE if successful, or FALSE if the image could not be loaded.
If format is specified, the loader attempts to read the image using the specified format. If format is not specified (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.
This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.
Returns the number of bytes occupied by the image data.
See also: bytesPerLine().
Returns the size of the color table for the image.
Notice that numColors() returns 0 for 32-bpp images, since these images do not use color tables, but instead encode pixel values as RGB triplets.
Returns TRUE if this image and i have different contents, and FALSE if they they have the same. This can be slow. Of course, this function returns quickly if e.g. the two images' widths are different.
See also: operator=().
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().
Assigns a shallow copy of image to this image and returns a reference to this image.
See also: copy().
Returns TRUE if this image and i have the same contents, and FALSE if they differ. This can be slow. Of course, this function returns quickly if e.g. the two images' widths are different.
See also: operator=().
[static]Returns a list of image formats which are supported for image output.
Returns the actual color of the pixel at the given coordinates.
If (x,y) is not on the image, the results are undefined.
Examples: qmag/qmag.cpp
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.
Returns the enclosing rectangle (0,0,width(),height()) of the image.
See also: width(), height() and size().
Resets all image parameters and deallocates the image data.
Examples: qtimage/qtimage.cpp
Saves the image to the file fileName, using the image file format format. Returns TRUE if successful, or FALSE if the image could not be saved.
See also: load(), loadFromData(), imageFormat(), QPixmap::save() and QImageIO.
Returns a pointer to the pixel data at the i'th scanline.
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() and friends (qcolor.h)
to access the pixels.
See also: bits().
Examples: desktop/desktop.cpp
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().
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().
Examples: desktop/desktop.cpp
Resizes the color table to numColors colors.
If the color table is expanded, then all new colors will be set to black (RGB 0,0,0).
See also: color() and setColor().
Sets the pixel index or color at the given coordinates.
If (x,y) is not valid, or if the image is a paletted image (depth() <= 8) and index_or_rgb >= numColors(), the results are undefined.
Returns the size of the image.
See also: width(), height() and rect().
Returns a copy of the image smoothly scaled to width by height pixels. For 32-bpp images, and 1-bpp/8-bpp color images, the result will be 32-bpp, while 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 - 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.
[static]Determines the bit order of the display hardware. Returns QImage::LittleEndian (LSB first) or QImage::BigEndian (MSB first).
[static]Determines the host computer byte order. Returns QImage::LittleEndian (LSB first) or QImage::BigEndian (MSB first).
Tests if the ( x, y ) is a valid coordinate in the image.
Examples: qmag/qmag.cpp
Returns the width of the image.
See also: heigth(), size() and rect().
Writes an image to the stream as a BMP image.
See also: QImage::save().
Reads an image from the stream.
See also: QImage::load().
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