We need the definition in the spec, if for any reason to avoid getting the wrong interpretation.
Yes, some platforms align on words (I have seen 16-, 32-, and 64-bit alignment), but for PWG (CUPS) Raster we want 8-bit (octet) alignment. In practice this means that we only have extra/leftover bits for the 1-bit grayscale/black case since the other depths supported in PWG Raster are 8- and 16-bits per color.
On Apr 28, 2011, at 1:22 PM, Petrie, Glen wrote:
> Mike,
>> Question on your definition of bytes-per-line (BPL): You have it ending at an octet (8-bit) but I have seen cases where the boundary is at the word or 32-bit level. In fact, I have seen were people clip a line by changing the number of pixel per line but not the bytes-per-line. What has been your experience? Suggestion: Leave the equation out of specification and it is understood or is stated that new raster lines begin at multiples of bpl.
>> Glen
>>> From: Michael Sweet [mailto:msweet at apple.com]
> Sent: Thursday, April 28, 2011 10:27 AM
> To: Petrie, Glen
> Cc: ipp at pwg.org> Subject: Re: [IPP] (PWG) Raster Question on what is required
>> On Apr 28, 2011, at 10:21 AM, Petrie, Glen wrote:
>> ...
>> libtiff (the most widely-used TIFF library) supports 16-bits per color.
>>>> I must be looking at the wrong version because TIFF 6.0 shows only <8,8,8> http://www.libtiff.org/support.html>> Hmm, they must have removed 16-bit support at one point - back when I was doing print software for SGI workstations the "Sam Leffler" version of libtiff supported it...
>>> ...
> I think for interoperability we want a minimum set for interoperability (and to address the use cases/design requirements). But most values of color space and bit depth should be optional.
>> Ok, then from your color-spaces, the required bits-per-color would 1 and 8. Also, the required bits-per-pixel would be 1, 8, 24
>> Right.
>>> One more time. Does conformance to pwg-raster-back-side mean “the printer will perform the indicated transforms” or this is an identifier stating what the “state” of the back-side image is?
>> Conformance for a printer means that it will advertise what it needs. For a client it means the client will transform the back side images as indicated by the printer.
>> ________________________________________________________________________
> Michael Sweet, Senior Printing System Engineer, PWG Chair
>
__________________________________________________
Michael Sweet, Senior Printing System Engineer, PWG Chair
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