Luminous Landscape Forum

Raw & Post Processing, Printing => Printing: Printers, Papers and Inks => Topic started by: paulbk on April 04, 2006, 06:40:12 pm

Title: Hahnemühle "black point compensation" off
Post by: paulbk on April 04, 2006, 06:40:12 pm
re: Black Point Compensation: Off

This from the Hahnemühle ICC-Profile site:
"Intent: Perceptual, Black Point Compensation: Off."

Go here Hahnemuehle (http://72.14.203.104/search?q=cache:WanC4ZtfMhMJ:www.hahnemuehle.com/site/en/472/epson.html+site:www.hahnemuehle.com+%22black+point+compensation%22&hl=en&gl=us&ct=clnk&cd=1)
Scroll to bottom of page.

Has anyone used these settings with Epson driver (no RIP)? Results? Comments?
Title: Hahnemühle "black point compensation" off
Post by: alainbriot on April 04, 2006, 06:56:09 pm
Quote
re: Black Point Compensation: Off
This from the Hahnemühle ICC-Profile site:
"Intent: Perceptual, Black Point Compensation: Off."
[a href=\"index.php?act=findpost&pid=61818\"][{POST_SNAPBACK}][/a]

This is the standard approach when using Perceptual Intent. Black point compensation (BPC) is not checked during conversion because Perceptual is white point and black point relative.  

BPC must be check if using Relative Colorimetric (relcol) because relcol is white point relative and black point absolute.

The 2 other intents (saturation and absolute colorimetric) are not recommended for photographic printing.

Alain
Title: Hahnemühle "black point compensation" off
Post by: paulbk on April 04, 2006, 07:22:00 pm
Thank you very much Alain. I've always been told to leave BPC 'on', no matter what the rendering intent.

p
Title: Hahnemühle "black point compensation" off
Post by: alainbriot on April 04, 2006, 07:52:00 pm
Quote
Thank you very much Alain. I've always been told to leave BPC 'on', no matter what the rendering intent.
p
[a href=\"index.php?act=findpost&pid=61825\"][{POST_SNAPBACK}][/a]

Only with relcol.  Not necesary with perceptual.

It's not a very well understood aspect of color management which explains the many different opinions that are out there.  My current work focuses on color and that's why this is important to me.  Note that these settings are valid with both the Epson (or other brand) driver and RIPs (I use imageprint).

Alain
Title: Hahnemühle "black point compensation" off
Post by: digitaldog on April 05, 2006, 10:01:44 am
I don't agree with their recommendation at all! IF there's an issue with black mapping in the profile, BPC will help a great deal. IF the profile has no issue, it does nothing. There's a PDF on my site that explains what BPC does. Unless you have a really screwed up profile, you always want it on. IOW, it either helps or does nothing.
Title: Hahnemühle "black point compensation" off
Post by: paulbk on April 05, 2006, 05:41:10 pm
It’s no wonder mere mortals like me are confused. Alain Briot makes stunning world class prints and Andrew Rodney is a world class digital color guru, and yet they don’t see BPC the same way. Oye vey!

You’d think the move to digital would make post processing and printing more scientific and therefore deterministic. Nope.
Title: Hahnemühle "black point compensation" off
Post by: Stephen Best on April 05, 2006, 07:05:41 pm
Quote
I don't agree with their recommendation at all! IF there's an issue with black mapping in the profile, BPC will help a great deal. IF the profile has no issue, it does nothing. There's a PDF on my site that explains what BPC does. Unless you have a really screwed up profile, you always want it on. IOW, it either helps or does nothing.
[{POST_SNAPBACK}][/a] (http://index.php?act=findpost&pid=61878\")
I struggled with the same thing and decided that, on the range of rag papers I use with the Epson driver, I got better results with it "Off" (Perceptual only). I note that BPC "Off" is also the recommendation of a number of paper manufacturers (Hahnemühle, Crane ... links below). I don't think they propose this simply to inflate apparent Dmax. Maybe if your shadows were clipped, BPC "On" may be more useful. With Rel/Col however and the Epson driver, BPC "Off" is a disaster.

I'd be interested to know your reasoning why you think BPC could be beneficial with Perceptual. The results I've seen don't seem to bear this out.

[a href=\"http://www.hahnemuehle.com/site/en/470/epson.html]http://www.hahnemuehle.com/site/en/470/epson.html[/url]
http://www.crane.com/museo/profiles.aspx (http://www.crane.com/museo/profiles.aspx)
Title: Hahnemühle "black point compensation" off
Post by: digitaldog on April 05, 2006, 07:18:32 pm
Quote
I'd be interested to know your reasoning why you think BPC could be beneficial with Perceptual. The results I've seen don't seem to bear this out.

The rendering intent should be immaterial. Now I don't know who's profiles you're using or how they are handling a Perceptual intent. There is absolutely no standard in how a manufacturer builds a perceptual rendering. To Quote myself:

Because there is no standard specification for how ICC profiles map solid black from the source color space to the destination color space, there are cases where the solid black of an image can produce less than solid black in the resulting converted image.
To correct these possible problems,Adobe has a switch in the ACE CMM called Black Point
Compensation. Turning this switch on causes ACE to ignore the actual luminance of black in
the source color space.With this switch on,the darkest black in the source space is mapped to
the darkest black in the destination.

So, is there a compelling reason you don't want to map Black this way? I've seen some wacky RGB profiles that produce poor results with BPC but I haven't run into one in years. As I said, if there's an issue with the black mapping, BPC helps. If there isn't, it does nothing. If you uncheck it, you'll either see no change, or you'll see why you generally want it turned on.
Title: Hahnemühle "black point compensation" off
Post by: digitaldog on April 05, 2006, 07:25:53 pm
One company is using Fuji's ColorKit to build the profiles. I have a copy but dont' use it (it's OK but not anywhere near the top of my list).

The other is using ProfileMaker Pro. I imported the profile so I can see the settings they are using. I can't fathom why they are using the settings they are (Logo Classic, Neutral Paper, small profile size). They may have a reason and I don't think this has anything to do with BPC but these are settings I personally wouldn't nor do not use when I build profiles.
Title: Hahnemühle "black point compensation" off
Post by: Stephen Best on April 05, 2006, 07:43:27 pm
Quote
So, is there a compelling reason you don't want to map Black this way?
I agree, it sounds like the logical thing ... but practice is different. I found on rag BPC "On" either did nothing or pushed the shadows way too high. The same with both custom and downloaded profiles. Some other manufacturer (which currently eludes me) stated that BPC "On" or "Off" was a judgment call and they wouldn't want to make a recommendation either way. It all sounds like voodoo to me. Anyway, I'll stick with what gives me the best results for now until I can afford to move to a RIP and build my own CMYK profiles.
Title: Hahnemühle "black point compensation" off
Post by: Stephen Best on April 06, 2006, 12:49:18 am
Quote
There's a PDF on my site that explains what BPC does. Unless you have a really screwed up profile, you always want it on.
Obviously not this one:

http://www.digitaldog.net/files/Black_Point_Compensation.pdf (http://www.digitaldog.net/files/Black_Point_Compensation.pdf)

:-)
Title: Hahnemühle "black point compensation" off
Post by: Brian Gilkes on April 07, 2006, 06:26:34 pm
The plot and perhaps the air thickens.
I received my first roll of Silver Rag yesterday. Last night I downloaded the Crane canned profile (perceptual and BPC off). I'm about to print test charts per Crane recommendation and with my standard settings , print both on the 9800, and send to Les Walkling to read and build custom profiles.
We'll see what comes up. I would strongly suspect that with a colour space big enough to encompass the K3 ink gamut the answer is a custom profile using Rel Col and BPC on.
Cheers
Brian.
www.pharoseditions.com.au
Title: Hahnemühle "black point compensation" off
Post by: Landscapes on April 07, 2006, 09:45:57 pm
Hey Brian,

I'm waiting for my roll of Silver Rag to come in as well.  Its coming by accident actually cause I first ordered it, but then cancelled it after reading about the Fine Art Pearl paper, but I guess its on its way nevertheless.  Anyway, I'm reading about how glossy it is, and I wonder if you can give me your personal description.  I now have an Epson 4800 cause my 4000 had to be replared by Epson, and I'm missing my matte paper.  I really hoped that these new papers would be a substitute for matte in that you can print on it with the PK ink, but that they had a matte (non shinny) surface.

So I realize its kind of like a pearl now, but can you elborate any?  I have experience with Epson's Premium Luster and Semi-matte.  What I'd want is something close to enhanced matte, or ultra smooth fine art paper, but I think I'm dreaming.  So should I even open the box up.. will I be dissapointed?  I just don't like the reflections from these papers under glass.

Kiran
Title: Hahnemühle "black point compensation" off
Post by: TomTom60 on April 08, 2006, 02:09:27 am
Kiran,

Are you wondering whether Crane Silver rag is "like a pearl"?? is that correct?

Silver rag is nothing like a pearl surface. It is a glossy, bumpy surface on a warm, heavy base sheet. Think semi-matte only with bigger bumps. If it is not illuminated correctly it will pick up highlights in the bumps...stipples, whatever you want to call them. It has a defined texture that seems to become more apparent when you lay ink onto it. You can make beautiful prints with it and as long as they are lit properly (from above with the light source about 30 or so degrees from the wall) they will look grand. I dont like the texture. Im much more interested in the offerings from Innova/Da Vinci and perhaps the Hannemuhley "Pearl" surface...not sure what this describes yet...I have to see it i think.

These papers are not a substitute for matte papers where you can print with the blacker PK ink. they are the beginnings of an answer for a real, bw, fine art printing stock.

 In some sense..matte papers were a replacement for these papers because these papers didnt exist before. These papers are designed to fill a gap that has existed since high quality digital printing was available. The need for a paper that really looked as good as a traditional black and white print.

Matte papers became the go to paper because they looked better than the rc papers AND because they didnt show itches like gloss differential or bronzing. the trade off here is the lack of real black in the MK ink. K3 inks have almost eliminated..almost...these problems so now these "traditional gloss" papers are coming out in droves. Thanks be to those who finally have put effort towards designing a paper that looks close to a real black and white print.
Title: Hahnemühle "black point compensation" off
Post by: Hermie on April 08, 2006, 04:41:59 pm
Quote
Obviously not this one:

http://www.digitaldog.net/files/Black_Point_Compensation.pdf (http://www.digitaldog.net/files/Black_Point_Compensation.pdf)

:-)
[{POST_SNAPBACK}][/a] (http://index.php?act=findpost&pid=61989\")


This one explains what BPC does:
[a href=\"http://www.color.org/Adobe1bpc.pdf]http://www.color.org/Adobe1bpc.pdf[/url]

Herman
Title: Hahnemühle "black point compensation" off
Post by: Stephen Best on April 08, 2006, 06:37:29 pm
Quote
This one explains what BPC does:
http://www.color.org/Adobe1bpc.pdf (http://www.color.org/Adobe1bpc.pdf)

Herman
[a href=\"index.php?act=findpost&pid=62172\"][{POST_SNAPBACK}][/a]
Thanks for the detailed description. Obviously this isn't a precise science, it depends on the shape of the space etc., which explains why the results are variable.

I was only pointing out to Andrew that his recommendations today contradict those from his earlier paper, written then for PS5.
Title: Hahnemühle "black point compensation" off
Post by: Mark D Segal on April 09, 2006, 11:04:01 am
Fraser, Murphy and Bunting as well as Fraser & Blatner (Real World Color Management and Real World Photoshop CS2 respectively) are unequivocal that BPC should be enabled at all times, unless one is experimenting to see what difference it makes. Fraser and Blatner have a particularly lucid explanation for this recommendation in their inset on page 210 titled "Black is Black (or Is It?). Nothing in any of these explanations suggests that the decision whether or not to use BPC depends on the paper. Of course newer inkjet printing papers have appeared on the market since these books were published, but the principles described therein don't indicate a logic that would be influenced by the characteristics of the paper - at least none that is not obvious to me.
Title: Hahnemühle "black point compensation" off
Post by: Wills on April 09, 2006, 02:40:56 pm
I have all my papers and inksets custom profiled and I see little if any difference on the BPC state. However initially using stock profiles, well I could yeah there are cases for using and not using it.
Title: Hahnemühle "black point compensation" off
Post by: bruce fraser on April 16, 2006, 10:29:01 pm
Black Point Compensation in Photoshop 5.x was unsafe for RGB-to-RGB conversions and often produced hideous results, which is probably why Andrew recommended leaving it turned off for inkjet printing from Photoshop 5.x.

It got fixed in Photoshop 6. Now it either does nothing, or it makes sure that black in the source is mapped to black in the image. I've yet to find a situation where this wasn't desirable behavior, though it has sometimes led me to edit the image to close the shadows down a little.

Compressing shadows is pretty much always a safe operation. But if the shadow detail has been clipped, which often happens with BPC turned off, there's nothing you can do to open them up again.

While its effect is usually more subtle with Perceptual rendering than with relcol, it's equally necessary with some pairs of source and destination profile in perceptual and in relcol. If an image looks significantly better with BPC turned off, the first thing I'd do is to check all the profiles involved....
Title: Hahnemühle "black point compensation" off
Post by: Stephen Best on April 17, 2006, 12:33:30 am
Quote
While its effect is usually more subtle with Perceptual rendering than with relcol ...

Why is there a difference at all between the two? This to me implies that perceptual munges the black point along with the gamut and what you're getting with BPC is (sometimes) a double adjustment ... whereas relcol by itself has no means to adjust the black point and is reliant on outside help (BPC) to address it.

Why, if I soft-proof an image with a profile for rag (with an obvious difference in the blacks and a value set for the black point tristimulus) don't I see a change on-screen when I toggle BPC with perceptual rendering?

Lastly why, since there's an obvious requirement, hasn't this been incorporated into the ICC specs?

Questions, questions ... :-)
Title: Hahnemühle "black point compensation" off
Post by: 32BT on April 17, 2006, 06:33:50 am
At the current state of affairs there is a difference between relcol and perceptual, because most profiling sw incorporate a form of BPC in the perceptual tables, which basically means that the blackest black is noted as having an L = 0 value. In such cases, Photoshop will skip its own routines for BPC, even if it's switched on.

BPC is not incorporated in the ICC specs, since it is not an obvious requirement other than for perceptual renderings. And for perceptual intent, the ICC can not make a recommendation, because it is then still open what curve is used for the compensation. A simple linear scaling? Or some form of shadow compression as is the case with Adobe's bpc. In other words, it becomes a judgement call.

And also there is one very important case where BPC is very much NOT a requirement and is to be switched off: namely If you want to make a press proof where the proofing printer blackpoint is darker than the press print blackpoint. In order to faithfully reproduce the lighter black point, you need to switch BPC off.

If you truly want to see the effect of BPC including its shadow compression, you always need to use the Photoshop softproof feature and switch the Black Point Simulation on. This will lighten the blacks if applicable, and allows you to better judge the effect of blacks relative to saturation. If you leave this off, some dark saturated colors may look oversaturated in preview. This is particularly apparent in dark, shadowed skintones...!

Having said all this, I must admit that the first profile I tried from the HM website (FineArt Canvas at the bottom) is indeed influenced by Photoshop BPC, even with Perceptual intent. However, not necessarily in a bad way, and likely because of a less than optimal perceptual table in the profile.


Quote
Why is there a difference at all between the two?

Lastly why, since there's an obvious requirement, hasn't this been incorporated into the ICC specs?

Questions, questions ... :-)
[a href=\"index.php?act=findpost&pid=62771\"][{POST_SNAPBACK}][/a]
Title: Hahnemühle "black point compensation" off
Post by: Stephen Best on April 17, 2006, 08:13:46 am
Quote
At the current state of affairs there is a difference between relcol and perceptual, because most profiling sw incorporate a form of BPC in the perceptual tables, which basically means that the blackest black is noted as having an L = 0 value. In such cases, Photoshop will skip its own routines for BPC, even if it's switched on.

BPC is not incorporated in the ICC specs, since it is not an obvious requirement other than for perceptual renderings. And for perceptual intent, the ICC can not make a recommendation, because it is then still open what curve is used for the compensation. A simple linear scaling? Or some form of shadow compression as is the case with Adobe's bpc. In other words, it becomes a judgement call.

And also there is one very important case where BPC is very much NOT a requirement and is to be switched off: namely If you want to make a press proof where the proofing printer blackpoint is darker than the press print blackpoint. In order to faithfully reproduce the lighter black point, you need to switch BPC off.

If you truly want to see the effect of BPC including its shadow compression, you always need to use the Photoshop softproof feature and switch the Black Point Simulation on. This will lighten the blacks if applicable, and allows you to better judge the effect of blacks relative to saturation. If you leave this off, some dark saturated colors may look oversaturated in preview. This is particularly apparent in dark, shadowed skintones...!

Having said all this, I must admit that the first profile I tried from the HM website (FineArt Canvas at the bottom) is indeed influenced by Photoshop BPC, even with Perceptual intent. However, not necessarily in a bad way, and likely because of a less than optimal perceptual table in the profile.
[a href=\"index.php?act=findpost&pid=62778\"][{POST_SNAPBACK}][/a]

The fact that perceptual tables incorporate some form of compensation of their own is borne out by my experience. The way I interpret Adobe's implementation of BPC however is that it's not just shadow compression, but an overall luminance compression of the image (see the referenced Adobe description). I still don't see a change in the soft-proof when toggling BPC when Simulate Black Ink (which I assume is what you meant) is on, even though the profile's black point isn't L=0 ... though I admit I haven't tested whether it makes a difference on output with the current paper/profile combination I'm using.

So to clarify, if the perceptual table is doing BPC it will set the black point L=0 which will nullify Photoshop's BPC (since there's no adjustment). And if it isn't, then you do want Photoshop to do it. What concerns me is that it seems some profiles are doing some compensation but still affected by Photoshop's. I'm not sure that hard and fast rules such as "always use BPC" applies in the last case and it seems best to test which gives the optimum results.

Thanks for your input.
Title: Hahnemühle "black point compensation" off
Post by: 32BT on April 17, 2006, 08:53:15 am
Agreed. Testing is paramount in such a case. Though I also agree with the idea that if you run into such a profile, then its usually the profile that is suspect. So if you build your own custom profiles and BPC does indeed affect the perceptual rendering, then it may be useful to review the profile build settings. For example, the max density discussed in another thread might be a culprit, and selecting a different papertype in the printer driver prior to profiling may alleviate the problem.

Quote
What concerns me is that it seems some profiles are doing some compensation but still affected by Photoshop's. I'm not sure that hard and fast rules such as "always use BPC" applies in the last case and it seems best to test which gives the optimum results.
Title: Hahnemühle "black point compensation" off
Post by: Hermie on December 26, 2006, 09:30:20 am
This is what Adobe says about BPC and rendering intents:

"Typically, BPC is performed for conversions using the Relative Colorimetric intent. BPC is not available for conversions using Absolute Colorimetric intent.

Color conversion using Perceptual intent already maps source white to destination white and source black to destination black. Because this mapping preserves the relationships of the shades, it is unlikely that a whole shadow section will be mapped to the same black value. Therefore, BPC should not be necessary. BPC is available, however, for this rendering intent, to be used with malformed profiles. For a given picture, the user can decide whether using BPC improves the color conversion and can select it or deselect it accordingly.

BPC is available for color conversion using the Saturation intent. As with Perceptual intent, the user may or may not find that selecting BPC improves the conversion of a given image."

Source: 'Adobe Systems' Implementation of Black Point Compensation' http://partners.adobe.com/public/developer...df/AdobeBPC.pdf (http://partners.adobe.com/public/developer/en/pdf/AdobeBPC.pdf) See paragraph 6.2

Herman
Title: Hahnemühle "black point compensation" off
Post by: jjlphoto on December 26, 2006, 11:03:26 am
Why not look at the image in soft proof and see whether on or off looks best? Theory only gets you so far, the rest is personal taste and making tests.