Controling bit-depth of gs output

[Tomasz Koprowski]

Hello,
I've developed a rastertospp filter that supports Samsung SPP-2020 photo printer. It works well enough on my config: DDK 1.2.3 + CUPS 1.2.8 + EPS GS 8.15.3, however a user with CUPS 1.3.6 and GPL GS 8.61 (with cups support) reports a problem I can't track down.

>From the logs it seems that for some reason cups-raster produced by gs is 1-bit per pixel instead of expected 24-bpp. (It makes no sense to support anything else on a photo-only printer anyway).

The PPD file has following lines regarding color models:
------------------------------8<---------------------------------------
*ColorDevice: True
*DefaultColorSpace: RGB
*OpenUI *ColorModel/Color Mode: PickOne
*OrderDependency: 10.0 AnySetup *ColorModel
*DefaultColorModel: RGB
*ColorModel RGB/Color: "<</cupsColorSpace 1/cupsColorOrder 0/cupsCompression 0>>setpagedevice"
*CloseUI: *ColorModel
*OpenUI *Resolution: PickOne
*DefaultResolution: 300dpi
*Resolution 300dpi/300 DPI: "<</HWResolution[300 300]/cupsBitsPerColor 8/cupsRowCount 0/cupsRowFeed 0/cupsRowStep 0>>setpagedevice"
*CloseUI: *Resolution
*CloseUI: *Resolution
------------------------------8<---------------------------------------

I've done some tests and on my system gs works correctly when called _from inside of cups_ (generates 24-bpp) so printing works as expected, which is not the case with the aforementioned user.

However when I call gs by hand I can't force it generate 24-bpp cups-raster and it outputs 1-bpp even though PPD file is set through env variable.

Therefore I conclude there is something I don't grasp regarding setting the gs output mode. Could anyone please clarify how it works?

Cheers,
Tomek