class QPixelFormat

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

Synopsis

Methods

Note

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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.

class FieldWidth
class Field
class ColorModel

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

Constant

Description

QPixelFormat.RGB

The color model is RGB.

QPixelFormat.BGR

This is logically the opposite endian version of RGB. However, for ease of use it has its own model.

QPixelFormat.Indexed

The color model uses a color palette.

QPixelFormat.Grayscale

The color model is Grayscale.

QPixelFormat.CMYK

The color model is CMYK.

QPixelFormat.HSL

The color model is HSL.

QPixelFormat.HSV

The color model is HSV.

QPixelFormat.YUV

The color model is YUV.

QPixelFormat.Alpha

There is no color model, only alpha is used.
class 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

Description

QPixelFormat.IgnoresAlpha

The alpha channel is not used.

QPixelFormat.UsesAlpha

The alpha channel is used.
class AlphaPosition

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

Constant

Description

QPixelFormat.AtBeginning

The alpha channel will be put in front of the color channels . E.g. ARGB.

QPixelFormat.AtEnd

The alpha channel will be put in the back of the color channels. E.g. RGBA.
class AlphaPremultiplied

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

Constant

Description

QPixelFormat.NotPremultiplied

The alpha channel is not multiplied into the color channels.

QPixelFormat.Premultiplied

The alpha channel is multiplied into the color channels.
class 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.

../../_images/qpixelformat-argb32buffer.png

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

Description

QPixelFormat.UnsignedInteger

QPixelFormat.UnsignedShort

QPixelFormat.UnsignedByte

QPixelFormat.FloatingPoint
class 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 separate color channels invalid. Instead the different YUV layouts are described with this enum.

Constant

Description

QPixelFormat.YUV444

QPixelFormat.YUV422

QPixelFormat.YUV411

QPixelFormat.YUV420P

QPixelFormat.YUV420SP

QPixelFormat.YV12

QPixelFormat.UYVY

QPixelFormat.YUYV

QPixelFormat.NV12

QPixelFormat.NV21

QPixelFormat.IMC1

QPixelFormat.IMC2

QPixelFormat.IMC3

QPixelFormat.IMC4

QPixelFormat.Y8

QPixelFormat.Y16
class 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

Description

QPixelFormat.LittleEndian

The byte order is little endian.

QPixelFormat.BigEndian

The byte order is big endian.

QPixelFormat.CurrentSystemEndian

This enum will not be stored, but is converted in the constructor to the endian enum that matches the enum of the current system.
__init__()

Creates a null pixelformat. This format maps to Format_Invalid .

__init__(colorModel, firstSize, secondSize, thirdSize, fourthSize, fifthSize, alphaSize, alphaUsage, alphaPosition, premultiplied, typeInterpretation[, byteOrder=QPixelFormat.ByteOrder.CurrentSystemEndian[, subEnum=0]])
Parameters:

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.

alphaPosition()
Return type:

AlphaPosition

Accessor function for alphaPosition.

alphaSize()
Return type:

int

Accessor function for the alpha channel size.

alphaUsage()
Return type:

AlphaUsage

Accessor function for alphaUsage.

bitsPerPixel()
Return type:

int

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

blackSize()
Return type:

int

Accessor function for the black/key color channel.

blueSize()
Return type:

int

Accessor function for the size of the blue color channel.

brightnessSize()
Return type:

int

Accessor function for the brightness channel size.

byteOrder()
Return type:

ByteOrder

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 CurrentSystemEndian as this value is translated to a endian value in the constructor.

channelCount()
Return type:

int

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.

colorModel()
Return type:

ColorModel

Accessor function for getting the colorModel.

cyanSize()
Return type:

int

Accessor function for the cyan color channel.

greenSize()
Return type:

int

Accessor function for the size of the green color channel.

hueSize()
Return type:

int

Accessor function for the hue channel size.

lightnessSize()
Return type:

int

Accessor function for the lightness channel size.

magentaSize()
Return type:

int

Accessor function for the megenta color channel.

__ne__(fmt2)
Parameters:

fmt2 – QPixelFormat

Return type:

bool

__eq__(fmt2)
Parameters:

fmt2 – QPixelFormat

Return type:

bool

premultiplied()
Return type:

AlphaPremultiplied

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

redSize()
Return type:

int

Accessor function for the size of the red color channel.

saturationSize()
Return type:

int

Accessor function for the saturation channel size.

subEnum()
Return type:

int

typeInterpretation()
Return type:

TypeInterpretation

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

yellowSize()
Return type:

int

Accessor function for the yellow color channel.

yuvLayout()
Return type:

YUVLayout

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.