[poppler] Migrating poppler to liblcms2 from liblcms1

[Maria, Marti]

Bon dia Albert,

That makes a lot of sense. Lcms2 spends more time on optimizing the transform in order to make it faster. That means create transform is currently slower that lcms1 but applying transforms  is way faster. This was indeed a design decision, as most of time creation of transforms happens only once at the very beginning and then this transform is applied to huge amounts of raster. The performance tests I send didn't take creation time into account.

I will take this action item to review creation time in the next release. Otherwise, you may consider reusing transforms. That would speed up both  lcms1 and lcms2.  If this is not feasible, there is a flags cmsFLAGS_NOOPTIMIZE, that makes transform creation fast, at the expense of slower dotransfom operation. This is not recommended at all because you disable all optimizations, but may solve the issue when creating transforms that are applied only to few bytes.

Again, thanks for reporting. I'm putting the transform creation time issue high in my priority list.

Best regards

Marti Maria,  Color Engineer
HP Large Format Printers Division - Barcelona
marti.maria at hp.com



-----Original Message-----
From: Albert Astals Cid [mailto:tsdgeos at gmail.com] On Behalf Of Albert Astals Cid
Sent: jueves, 26 de enero de 2012 19:43
To: poppler at lists.freedesktop.org
Cc: Maria, Marti; Till Kamppeter; seb128 at ubuntu.com
Subject: Re: [poppler] Migrating poppler to liblcms2 from liblcms1

El Dilluns, 23 de gener de 2012, a les 11:16:03, Maria, Marti va escriure:
> Hi,
> In my testings lcms2 is significantly faster that lcms1 except when 
> using floating point, then lcms2 favors precision.

Is this precision is so important to justify a 10x slowliness? Maybe it'd be a good idea to have a fallback fast mode for those not willing to take that 10x hit?

> http://littlecms2.blogspot.com/2010/03/xput-comparative-119-vs-20.html
> 
> Altona test does many different color conversions it would be 
> interesting to know which transformation is going slow.

Attached the callgrind output of running poppler there, you can see the time is almost totally spent on creating the transforms.

Wild guess: I'm wondering if the thing is that not transformations are all precalculated (meaning a faster overall if you do lots of access) and previously they were done each time and thus if we end up doing "few" 
transformations it was just much faster?

Cheers,
  Albert

> 
> Regards
> Marti
> 
> ________________________________________
> From: Till Kamppeter [till.kamppeter at gmail.com]
> Sent: Monday, January 23, 2012 8:58 AM
> To: Albert Astals Cid
> Cc: poppler at lists.freedesktop.org; Maria, Marti; Sebastien Bacher; 
> Koji Otani Subject: Re: [poppler] Migrating poppler to liblcms2 from 
> liblcms1 On 01/22/2012 11:18 PM, Albert Astals Cid wrote:
> > Same thing, altona_technical_1v2_x3.pdf still goes up from x seconds 
> > to 10x seconds when going from lcms1 to lcms2.
> > 
> > That is in my opinion not acceptable (of course i'm not ruling out 
> > that we in poppler are using lcms2 wrong). Till, does your ubuntu 
> > work cover fixing the regressions of moving from lcms1 to lcms2 or 
> > all your work covers is making stuff compile?
> 
> I downloaded altona_technical_1v2_x3.pdf from 
> http://www.eci.org/doku.php?id=es:downloads and tried pdftops on 
> Ubuntu Oneiric (11.10, lcms1) and on Precise (12.04, lcms2, Koji 
> Otani's patch) and with lcms1 it takes 3.5 seconds and with lcms2 17.5 seconds.
> 
> The same problem occurs with Ghostscript: There the same transition 
> happened from Oneiric to Precise and here Oneiric is much faster with 
> this file, too. In Precise PDF rendering for printing is done by 
> Ghostscript and not by Poppler, so lcms2 is already used for printing 
> in Precise for some time. As there are no performance complaints by 
> users yet, it seems that for everyday files there is not such a 
> significant performance loss. and this
> 
> Marti, can you check what is the problem with lcms2 and this PDF file 
> and also why most files are somewhat slower with lcms2?
> 
>     Till
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