pdfSetDeviceNChannelMask
Set or clear one channel in the DeviceN channel mask.
void pdfSetDeviceNChannelMask(PDFHandle pdf, int channelIdx, int on)
This function sets one channel in the DeviceN channel mask to "on" or
"off". The
channelIdx argument specifies the channel
number, and the on argument is non-zero for "on" or zero
for "off".
The pdfGetDeviceNToRGBBitmap uses a mask that controls which color
channels are included in the conversion. Channels that are "on" are
included; channels that are "off" do not contribute to the output
pixels. The channels are the same as reported by
pdfGetDeviceNChannelName. The mask only affects the output of
pdfGetDeviceNToRGBBitmap.
The DeviceN channel mask is automatically reset (all channels "on") on
each call to pdfConvertPageToDeviceNImage,
pdfConvertPageToDeviceNImageWithAlpha,
pdfConvertRegionToDeviceNImage, or
pdfConvertRegionToDeviceNImageWithAlpha.
C:
int nChannels, i;
char *channelName;
unsigned int channelCMYK;
PDFImageHeader hdr;
char *bits;
int err;
err = pdfConvertPageToDeviceNImage(pdf, pageNum, dpi);
if (err != pdfOk) {
/* handle the error */
...
}
pdfResetDeviceNChannelMask(pdf);
nChannels = pdfGetNumDeviceNChannels(pdf);
for (i = 0; i < nChannels; ++i) {
channelName = pdfGetDeviceNChannelName(pdf, i);
if ( ... ) {
pdfSetDeviceNChannelMask(pdf, 1);
} else {
pdfSetDeviceNChannelMask(pdf, 0);
}
}
pdfGetDeviceNToRGBBitmap(pdf, 4, &hdr, &bits);
... use the bitmap ...
/* the bitmap memory must be freed when you are finished */
pdfFreeMemory(bits);
/* free the internal storage used by pdfConvertPageToDeviceNImage */
pdfClearDeviceNImage(pdf);