Qt Reference Documentation

# Obsolete Members for QImage

The following class members are obsolete. They are provided to keep old source code working. We strongly advise against using them in new code.

- QImage class reference

## Public Functions

QImage | alphaChannel () const`(obsolete)`
int | serialNumber () const`(obsolete)`
void | setAlphaChannel ( const QImage & alphaChannel )`(obsolete)`

## Member Function Documentation

### QImage QImage::alphaChannel () const

Returns the alpha channel of the image as a new grayscale QImage in which each pixel's red, green, and blue values are given the alpha value of the original image. The color depth of the returned image is 8-bit.

You can see an example of use of this function in QPixmap's alphaChannel(), which works in the same way as this function on QPixmaps.

Most usecases for this function can be replaced with QPainter and using composition modes.

Warning: This is an expensive function.

See also setAlphaChannel(), hasAlphaChannel(), Pixmap, and Image Transformations.

### int QImage::serialNumber () const

Returns a number that identifies the contents of this QImage object. Distinct QImage objects can only have the same serial number if they refer to the same contents (but they don't have to).

Use cacheKey() instead.

Warning: The serial number doesn't necessarily change when the image is altered. This means that it may be dangerous to use it as a cache key.

See also operator==().

### void QImage::setAlphaChannel ( const QImage & alphaChannel )

Sets the alpha channel of this image to the given alphaChannel.

If alphaChannel is an 8 bit grayscale image, the intensity values are written into this buffer directly. Otherwise, alphaChannel is converted to 32 bit and the intensity of the RGB pixel values is used.

Note that the image will be converted to the Format_ARGB32_Premultiplied format if the function succeeds.

Use one of the composition modes in QPainter::CompositionMode instead.

Warning: This function is expensive.

See also alphaChannel(), Image Transformations, and Image Formats.