convertRegionToDeviceNImageWithAlpha
The rectangular region is specified by the x,y coordinates of its upper-left corner and its width and height - in bitmap coordinates, not PDF coordinates. That is, if the whole-page bitmap would have been 1000 pixels wide and 2000 pixels high, and you request a region with (x,y) = (0,0) and (w,h) = (1000,500), the resulting bitmap will be the top fourth of the page.
This function differs from convertRegionToDeviceNImage
in that it
skips the final page compositing step, and maintains an alpha bitmap.
The alpha bitmap can be retrieved with getDeviceNAlphaPicture
.
Note: The alpha bitmap is only useful with PDF files that have been constructed with a transparent background.
After calling convertRegionToDeviceNImage
:
- call
getNumDeviceNChannels
to retrieve the number of color channels - call
getDeviceNChannelName
andgetDeviceNChannelCMYK
to get the name and CMYK value for a particular channel - call
getDeviceNPicture
to get a bitmap for a particular channel - call
getDeviceNAlphaPicture
to get the alpha channel bitmap
clearDeviceNImage
to release the memory used by
convertRegionToDeviceNImageWithAlpha
.
To enable an overprint preview rasterization, call setConfig
to
set the overprintPreview
parameter before
calling convertRegionToDeviceNImage
: