[IPP] (PWG) Raster Question on what is required

[IPP] (PWG) Raster Question on what is required

Michael Sweet msweet at apple.com
Thu Apr 28 20:44:22 UTC 2011


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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