Man pages matching name qwtplotrasteritem in section 3:

QwtPlotRasterItem.3.en	debian 10 / libqwt-doc
QwtPlotRasterItem.3.en	debian 10 / libqwt5-doc
QwtPlotRasterItem.3.en	debian 11 / libqwt-doc
QwtPlotRasterItem.3.en	debian 12 / libqwt-doc