QPixelFormat Class

QPixelFormat is a class for describing different pixel layouts in graphics buffers. More...

Header:	#include <QPixelFormat>
qmake:	QT += gui
Since:	Qt 5.4

This class was introduced in Qt 5.4.

• List of all members, including inherited members

Public Types

enum	AlphaPosition { AtBeginning, AtEnd }
enum	AlphaPremultiplied { NotPremultiplied, Premultiplied }
enum	AlphaUsage { IgnoresAlpha, UsesAlpha }
enum	ByteOrder { LittleEndian, BigEndian, CurrentSystemEndian }
enum	ColorModel { RGB, BGR, Indexed, Grayscale, CMYK, …, Alpha }
enum	TypeInterpretation { UnsignedInteger, UnsignedShort, UnsignedByte, FloatingPoint }
enum	YUVLayout { YUV444, YUV422, YUV411, YUV420P, YUV420SP, …, Y16 }

Public Functions

	QPixelFormat(QPixelFormat::ColorModel colorModel, uchar firstSize, uchar secondSize, uchar thirdSize, uchar fourthSize, uchar fifthSize, uchar alphaSize, QPixelFormat::AlphaUsage alphaUsage, QPixelFormat::AlphaPosition alphaPosition, QPixelFormat::AlphaPremultiplied premultiplied, QPixelFormat::TypeInterpretation typeInterpretation, QPixelFormat::ByteOrder byteOrder = CurrentSystemEndian, uchar subEnum = 0)
	QPixelFormat()
QPixelFormat::AlphaPosition	alphaPosition() const
uchar	alphaSize() const
QPixelFormat::AlphaUsage	alphaUsage() const
uchar	bitsPerPixel() const
uchar	blackSize() const
uchar	blueSize() const
uchar	brightnessSize() const
QPixelFormat::ByteOrder	byteOrder() const
uchar	channelCount() const
QPixelFormat::ColorModel	colorModel() const
uchar	cyanSize() const
uchar	greenSize() const
uchar	hueSize() const
uchar	lightnessSize() const
uchar	magentaSize() const
QPixelFormat::AlphaPremultiplied	premultiplied() const
uchar	redSize() const
uchar	saturationSize() const
QPixelFormat::TypeInterpretation	typeInterpretation() const
uchar	yellowSize() const
QPixelFormat::YUVLayout	yuvLayout() const

Related Non-Members

QPixelFormat	qPixelFormatAlpha(uchar channelSize, QPixelFormat::TypeInterpretation typeInterpretation = QPixelFormat::UnsignedInteger)
QPixelFormat	qPixelFormatCmyk(uchar channelSize, uchar alphaSize = 0, QPixelFormat::AlphaUsage alphaUsage = QPixelFormat::IgnoresAlpha, QPixelFormat::AlphaPosition alphaPosition = QPixelFormat::AtBeginning, QPixelFormat::TypeInterpretation typeInterpretation = QPixelFormat::UnsignedInteger)
QPixelFormat	qPixelFormatGrayscale(uchar channelSize, QPixelFormat::TypeInterpretation typeInterpretation = QPixelFormat::UnsignedInteger)
QPixelFormat	qPixelFormatHsl(uchar channelSize, uchar alphaSize = 0, QPixelFormat::AlphaUsage alphaUsage = QPixelFormat::IgnoresAlpha, QPixelFormat::AlphaPosition alphaPosition = QPixelFormat::AtBeginning, QPixelFormat::TypeInterpretation typeInterpretation = QPixelFormat::FloatingPoint)
QPixelFormat	qPixelFormatHsv(uchar channelSize, uchar alphaSize = 0, QPixelFormat::AlphaUsage alphaUsage = QPixelFormat::IgnoresAlpha, QPixelFormat::AlphaPosition alphaPosition = QPixelFormat::AtBeginning, QPixelFormat::TypeInterpretation typeInterpretation = QPixelFormat::FloatingPoint)
QPixelFormat	qPixelFormatRgba(uchar redSize, uchar greenSize, uchar blueSize, uchar alphaSize, QPixelFormat::AlphaUsage alphaUsage, QPixelFormat::AlphaPosition alphaPosition, QPixelFormat::AlphaPremultiplied premultiplied = QPixelFormat::NotPremultiplied, QPixelFormat::TypeInterpretation typeInterpretation = QPixelFormat::UnsignedInteger)
QPixelFormat	qPixelFormatYuv(QPixelFormat::YUVLayout yuvLayout, uchar alphaSize = 0, QPixelFormat::AlphaUsage alphaUsage = QPixelFormat::IgnoresAlpha, QPixelFormat::AlphaPosition alphaPosition = QPixelFormat::AtBeginning, QPixelFormat::AlphaPremultiplied premultiplied = QPixelFormat::NotPremultiplied, QPixelFormat::TypeInterpretation typeInterpretation = QPixelFormat::UnsignedByte, QPixelFormat::ByteOrder byteOrder = QPixelFormat::LittleEndian)

Detailed Description

In Qt there is a often a need to represent the layout of the pixels in a graphics buffer. Internally QPixelFormat stores everything in a 64 bit datastructure. This gives performance but also some limitations.

QPixelFormat can describe 5 color channels and 1 alpha channel, each can use 6 bits to describe the size of the color channel.

The position of the alpha channel is described with a separate enum. This is to make it possible to describe QImage formats like ARGB32, and also describe typical OpenGL formats like RBGA8888.

How pixels are suppose to be read is determined by the TypeInterpretation enum. It describes if color values are suppose to be read byte per byte, or if a pixel is suppose to be read as a complete int and then masked.

There is no support for describing YUV's macro pixels. Instead a list of YUV formats has been made. When a QPixelFormat is describing a YUV format, the bitsPerPixel value has been deduced by the YUV Layout enum. Also, the color channels should all be set to zero except the fifth color channel that should store the bitsPerPixel value.

See also TypeInterpretation.

Member Type Documentation

enum QPixelFormat::AlphaPosition

This enum type is used to describe the alpha channels position relative to the color channels.

Constant	Value	Description
QPixelFormat::AtBeginning	0	The alpha channel will be put in front of the color channels . E.g. ARGB.
QPixelFormat::AtEnd	1	The alpha channel will be put in the back of the color channels. E.g. RGBA.

enum QPixelFormat::AlphaPremultiplied

This enum type describes the boolean state if the alpha channel is multiplied into the color channels or not.

Constant	Value	Description
QPixelFormat::NotPremultiplied	0	The alpha channel is not multiplied into the color channels.
QPixelFormat::Premultiplied	1	The alpha channel is multiplied into the color channels.

enum QPixelFormat::AlphaUsage

This enum describes if the alpha channel is used or not. Sometimes the pixelformat will have a size for the alpha channel, but the pixel format does actually not use the alpha channel. For example RGB32 is such a format. The RGB channels are 8 bits each, and there is no alpha channel. But the complete size for each pixel is 32. Therefore the alpha channel size is 8, but the alpha channel is ignored. Its important to note that in such situations the position of the alpha channel is significant.

Constant	Value	Description
QPixelFormat::IgnoresAlpha	1	The alpha channel is not used.
QPixelFormat::UsesAlpha	0	The alpha channel is used.

enum QPixelFormat::ByteOrder

This enum describes the ByteOrder of the pixel format. This enum is mostly ignored but have some use cases for YUV formats. BGR formats have their own color model, and should not be described by using the opposite endianness on an RGB format.

Constant	Value	Description
QPixelFormat::LittleEndian	0	The byte order is little endian.
QPixelFormat::BigEndian	1	The byte order is big endian.
QPixelFormat::CurrentSystemEndian	2	This enum will not be stored, but is converted in the constructor to the endian enum that matches the enum of the current system.

enum QPixelFormat::ColorModel

This enum type is used to describe the color model of the pixelformat. Alpha was added in 5.5.

Constant	Value	Description
QPixelFormat::RGB	0	The color model is RGB.
QPixelFormat::BGR	1	This is logically the opposite endian version of RGB. However, for ease of use it has its own model.
QPixelFormat::Indexed	2	The color model uses a color palette.
QPixelFormat::Grayscale	3	The color model is Grayscale.
QPixelFormat::CMYK	4	The color model is CMYK.
QPixelFormat::HSL	5	The color model is HSL.
QPixelFormat::HSV	6	The color model is HSV.
QPixelFormat::YUV	7	The color model is YUV.
QPixelFormat::Alpha	8	There is no color model, only alpha is used.

enum QPixelFormat::TypeInterpretation

This enum describes how each pixel is interpreted. If a pixel is read as a full 32 bit unsigned integer and then each channel is masked out, or if each byte is read as unsigned char values. Typically QImage formats interpret one pixel as an unsigned integer and then the color channels are masked out. OpenGL on the other hand typically interpreted pixels "one byte after the other", Ie. unsigned byte.

QImage also have the format Format_RGBA8888 (and its derivatives), where the pixels are interpreted as unsigned bytes. OpenGL has extensions that makes it possible to upload pixel buffers in an unsigned integer format.

The image above shows a ARGB pixel in memory read as an unsigned integer. However, if this pixel was read byte for byte on a little endian system the first byte would be the byte containing the B-channel. The next byte would be the G-channel, then the R-channel and finally the A-channel. This shows that on little endian systems, how each pixel is interpreted is significant for integer formats. This is not the case on big endian systems.

Constant	Value
QPixelFormat::UnsignedInteger	0
QPixelFormat::UnsignedShort	1
QPixelFormat::UnsignedByte	2
QPixelFormat::FloatingPoint	3

enum QPixelFormat::YUVLayout

YUV is not represented by describing the size of the color channels. This is because YUV often use macro pixels, making the concept of sperate color channels invalid. Instead the different YUV layouts are described with this enum.

Constant	Value
QPixelFormat::YUV444	0
QPixelFormat::YUV422	1
QPixelFormat::YUV411	2
QPixelFormat::YUV420P	3
QPixelFormat::YUV420SP	4
QPixelFormat::YV12	5
QPixelFormat::UYVY	6
QPixelFormat::YUYV	7
QPixelFormat::NV12	8
QPixelFormat::NV21	9
QPixelFormat::IMC1	10
QPixelFormat::IMC2	11
QPixelFormat::IMC3	12
QPixelFormat::IMC4	13
QPixelFormat::Y8	14
QPixelFormat::Y16	15

Member Function Documentation

QPixelFormat::QPixelFormat(QPixelFormat::ColorModel colorModel, uchar firstSize, uchar secondSize, uchar thirdSize, uchar fourthSize, uchar fifthSize, uchar alphaSize, QPixelFormat::AlphaUsage alphaUsage, QPixelFormat::AlphaPosition alphaPosition, QPixelFormat::AlphaPremultiplied premultiplied, QPixelFormat::TypeInterpretation typeInterpretation, QPixelFormat::ByteOrder byteOrder = CurrentSystemEndian, uchar subEnum = 0)

Creates a QPixelFormat which assigns its data to the attributes. colorModel will be put into a buffer which is 4 bits long.

firstSize secondSize thirdSize fourthSize fifthSize alphaSize are all meant to represent the size of a channel. The channels will be used for different uses dependent on the colorModel. For RGB the firstSize will represent the Red channel. On CMYK it will represent the value of the Cyan channel.

alphaUsage represents if the alpha channel is used or not.

alphaPosition is the position of the alpha channel.

premultiplied represents if the alpha channel is already multiplied with the color channels.

typeInterpretation is how the pixel is interpreted.

byteOrder represents the endianness of the pixelformat. This defaults to CurrentSystemEndian.

subEnum is used for colorModels that have to store some extra information with supplying an extra enum. This is used by YUV to store the YUV type The default value is 0.

QPixelFormat::QPixelFormat()

Creates a null pixelformat. This format maps to QImage::Format_Invalid.

QPixelFormat::AlphaPosition QPixelFormat::alphaPosition() const

Accessor function for alphaPosition.

uchar QPixelFormat::alphaSize() const

Accessor function for the alpha channel size.

QPixelFormat::AlphaUsage QPixelFormat::alphaUsage() const

Accessor function for alphaUsage.

uchar QPixelFormat::bitsPerPixel() const

Accessor function for the bits used per pixel. This function returns the sum of the color channels + the size of the alpha channel.

uchar QPixelFormat::blackSize() const

Accessor function for the black/key color channel.

uchar QPixelFormat::blueSize() const

Accessor function for the size of the blue color channel.

uchar QPixelFormat::brightnessSize() const

Accessor function for the brightness channel size.

QPixelFormat::ByteOrder QPixelFormat::byteOrder() const

The byte order is almost always set the byte order of the current system. However, it can be useful to describe some YUV formats. This function should never return QPixelFormat::CurrentSystemEndian as this value is translated to a endian value in the constructor.

uchar QPixelFormat::channelCount() const

Accessor function for getting the channelCount. Channel Count is deduced by color channels with a size > 0 and if the size of the alpha channel is > 0.

QPixelFormat::ColorModel QPixelFormat::colorModel() const

Accessor function for getting the colorModel.

uchar QPixelFormat::cyanSize() const

Accessor function for the cyan color channel.

uchar QPixelFormat::greenSize() const

Accessor function for the size of the green color channel.

uchar QPixelFormat::hueSize() const

Accessor function for the hue channel size.

uchar QPixelFormat::lightnessSize() const

Accessor function for the lightness channel size.

uchar QPixelFormat::magentaSize() const

Accessor function for the megenta color channel.

QPixelFormat::AlphaPremultiplied QPixelFormat::premultiplied() const

Accessor function for the AlphaPremultiplied enum. This indicates if the alpha channel is multiplied in to the color channels.

uchar QPixelFormat::redSize() const

Accessor function for the size of the red color channel.

uchar QPixelFormat::saturationSize() const

Accessor function for the saturation channel size.

QPixelFormat::TypeInterpretation QPixelFormat::typeInterpretation() const

Accessor function for the type representation of a color channel or a pixel.

See also TypeInterpretation.

uchar QPixelFormat::yellowSize() const

Accessor function for the yellow color channel.

QPixelFormat::YUVLayout QPixelFormat::yuvLayout() const

Accessor function for the YUVLayout. It is difficult to describe the color channels of a YUV pixel format since YUV color model uses macro pixels. Instead the layout of the pixels are stored as an enum.