How do I convert QImage in Format_ARGB32 data to a pointer unsigned int*?



  • I want to convert a QImage of format RGB888 to ARGB32 & fetch pixel data as unsigned int*.

    I can do the following to convert to ARGB32

    @QImage new = old.convertToFormat(QImage::Format_ARGB32);@

    However, are the pixels stored signed or unsigned?

    I need a pointer unsigned int* data, such that,

    an unsigned int (32 bits) holds a pixel in ARGB format, which from left to right is as follows:

    • the first 8 bits are for the alpha channel (and are ignored)
    • the next 8 bits are for the red channel
    • the next 8 bits are for the green channel
    • the last 8 bits are for the blue channel
      How do I do this?

  • Lifetime Qt Champion

    Hi,

    @quint32 argbPtr = reinterpret_cast<quint32>(newImage.bits())@

    And you should be good to go.

    EDIT: corrected cast type, sorry for the error



  • Then I will need to convert from quint32* to uint* or unsigned int*. How will I do that?
    [quote author="SGaist" date="1381869224"]Hi,

    @quint32 argbPtr = static_cast<quint32>(newImage.bits())@

    And you should be good to go.[/quote]



  • You should avoid using an int in this case, since you want it to be explicitly 32 bits. quint32 is exactly what you want and will be platform/compiler independent.



  • Umm.... 1st of all, doing
    quint32 argbPtr = static_cast<quint32>(newImage.bits())
    gives me an error.

    Secondly, I need to get uint*, since I have to pass it through another function belonging to some other library.

    [quote author="Timothy" date="1382019170"]You should avoid using an int in this case, since you want it to be explicitly 32 bits. quint32 is exactly what you want and will be platform/compiler independent.[/quote]



  • bq. quint32 argbPtr = static_cast<quint32>(newImage.bits())
    you forgot the *'s :-)



  • I still get an error:
    error: invalid static_cast from type 'uchar*' to type 'quint32*'
    [quote author="Timothy" date="1382020222"]bq. quint32 argbPtr = static_cast<quint32>(newImage.bits())
    you forgot the *'s :-)
    [/quote]



  • @uint bits = reinterpret_cast<uint>(image.bits());@

    or

    @uint bits = (uint)image.bits();@

    and check the sizeof(uint) to be sure is 4


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