What exactly is black point compensation?

Yes I 've Googled this and still can't work out what it does when printing
from Photoshop.
A simple explanation would be great.
regards
PeterH

My View

Re: What exactly is black point compensation?

I sure hope I am not the reason for the Perkoff Pop OFF of late
I can't see his posts (he is blocked and I catch his new nicks easily
now........ ) see he duped a few noobs into sparring.

KatWoman

Re: What exactly is black point compensation?

On Mon, 24 Jul 2006 16:46:09 -0400, "KatWoman"
of course I care for yours, Kat. That indeed is why it came to mind.
Like you said, I gave no surname, maybe that was clever -
and you said the trolls are quited, did you not, Kat...

Sari

Re: What exactly is black point compensation?

Geez! The guy was excited to find the answer to his question and he
gets slammed for picking the wrong name from a guy who's name is
similar to two first names. Wow.

BobLake

Re: What exactly is black point compensation?

hmm now that suggestion of nick is that implying you don't care for mine?
If it's any consolation I fill out all net inquiries with
first name: Kat
last name: Woman
so to insult me according to your rule I would be "woman"
"hey woman get me some pie!"
or if you love me I am Kat?
It is not safe to go on NG with my real name due to perverts and trolls
BTW DAVE you give no last name
so we can't call you by the sur
anyhow NG is not the most polite place as you may have noticed..at least the
trolls are quieted and not too much spam..

KatWoman

Re: What exactly is black point compensation?

Sometimes it makes a clearly observable difference sometimes just a
barely observable difference and sometimes it does not affect at all.
E.g. when converting between normal/common RGB working-spaces and
between RGB and Lab the BPC has no affect since in these profiles the
blackpoint tag is either missing or is set to 0.
When converting from/to a device ICC profile the BPC can affect (but not
always affects, depends on the information in the profile).
You can easily inspect if the BPC has an effect:
1)make two dupes of an image
2)convert dupe1 with BPC and dupe 2 without BPC
3)drag+shift dupe2 as a layer on top of dupe 1
4)put dupe 2 into difference layer mode
5)merge the layers, apperance is rather dark after this
6)do some scaling up using levels
7)Inspect the histogram. If the BPC affected the histogram shows it,
else the histogram is just a vertical line at level 0.
Because the output profiles are results of a huge amount of
interpolation + approximations it can happen with some profiles that the
BPC affects in such way that device RGB in the dark end will not be used
at all, e.g. once I found a profile of an online photoprinting service
that did not give any device RGB data in the range from level 0 to level
9. Since then I have been inspecting the behaviour of new output
profiles rather closely and finally I make a test run using the various
combinations (mainly intent and BPC).
I normally use relative intent and never use the perceptual intent.
Perceptual intent is just a perceptual tweak over the relative intent
but it is perceptual for the person who created the profile or profiler.
In my opinion that person has no perceptual say on my printing
experience (so, when required, I apply my own intent using an Action
that also convert to the printing space).
Timo Autiokari

Timo Autiokari

Re: What exactly is black point compensation?

On Sun, 23 Jul 2006 15:30:43 -0400, "KatWoman"
lol...!!! You did not miss the name I suggested, Katwoman.... surely
you didn't miss it :-O
Dave

Dave

Re: What exactly is black point compensation?

what a whack-job you are Dave!
never figured you'd get so fired up over a name thing but the explanation
was really interesting, not the usual NG chat..

KatWoman

Re: What exactly is black point compensation?

When I soft proof with Epson's 2200 profiles in PS CS, I can't seem to
notice any difference with BPC on and off. Nor can I see any difference
in the prints. What does that say about these profiles, or my eyesight?
Also, when converting from another color space to srgb in PS CS, BPC is
an option. Similarly, I can't see any difference in Preview with it
on/off.
For his profiles, I think Bill Atkinson turns BPC off for Perceptual
rendering, and on for Relative Colorimetric rendering. So BPC does make
a difference to him. I could be wrong here.
Should BPC make any observable difference to the mere mortals?

Elementary@att.net

Re: What exactly is black point compensation?

rote:
It is obvious Peter, that I have been to much in a hurry in replying,
and not the first time:-(
2 reasons for it this time, which may be mitigating (w?) -
I simply hate it when somebody get called by his surname, and Mike's
answer to you made it very clear that Russell is his surname. It
recalls the time in the army where officers called a troopy by his
surname, and getting sent to detention barracks if they do attack
an officer because of it. When talking about people like mugabe
(zimbabwe) you do it by his surname because of the contempt he
deserves.
You did not even post under a name. There was somebody posting on
this group with a question regarding something and he needed a file.
I sent it to him, finding he used a false address, which he should
have explained, if he was looking for a file. His reaction when I
pointed it out to him, was sarcastic. Never mind, I then posted this
file to my homepage, and gave him the URL, and he downloaded it,
without even coming back with a thank you. Whether he posted
again, is unknown.
He posted without a name as well.
This morning I had two calls, one from a woman (not lady but simply
woman) and the other from a man, in reaction to an advert in a
newspaper for property to let. Both telephone numbers showed
'withheld' on my cell phone, and after telling them the property was
already taken, they simply dropped the line.
Why? Because they phoned nameless - without even a number to trace.
I wish my advice could have been (half as much) worth following like
Mike's, but it's not. Mike have already forgotten what I still should
learn.
Sorry for calling you a stupid fool. If you was one, you would not
have replied. Don't write without using a name. Even if calling
yourself *dogman*, use a name.
Keep well,
Dave
Here are the links to those much-talked-about
Crime Reporting Websites :
http://www.crimexposouthafrica.co.za
http://www.southafricaiscrap.blogspot.com
http://deathofjohannesburg.blogspot.com
http://www.wea.co.za/

Dave

Re: What exactly is black point compensation?

On Sat, 22 Jul 2006 22:55:41 GMT, "My View" <no spam ple@se.com>
wrote:
It is obvious Peter, that I have been to much in a hurry in replying,
and not the first time:-(
2 reasons for it this time, which may be mitigating (w?) -
I simply hate it when somebody get called by his surname, and Mike's
answer to you made it very clear that Russel is his surname. It
recalls the time in the army where officers called a troopy by his
surname, and getting sent to detention barracks if they do attack
an officer because of it. When talking about people like mugabe
(zimbabwe) you do it by his surname because of the contempt he
deserves.
You did not even post under a name. There was somebody posting on
this group with a question regarding something and he needed a file.
I sent it to him, finding he used a false address, which he should
have explained, if he was looking for a file. His reaction when I
pointed it out to him, was sarcastic. Never mind, I then posted this
file to my homepage, and gave him the URL, and he downloaded it,
without even coming back with a thank you. Whether he posted
again, is unknown.
He posted without a name as well.
This morning I had two calls, one from a woman (not lady but simply
woman) and the other from a man, in reaction to an advert in a
newspaper for property to let. Both telephone numbers showed
'withheld' on my cell phone, and after telling them the property was
already taken, they simply dropped the line.
Why? Because they phoned nameless - without even a number to trace.
I wish my advice could have been (half as much) worth following like
Mike's, but it's not. Mike have already forgotten what I still should
learn.
Sorry for calling you a stupid fool. If you was one, you would not
have replied. Don't write without using a name. Even if calling
yourself *dogman*, use a name.
Keep well,
Dave
Here are the links to those much-talked-about
Crime Reporting Websites :
http://www.crimexposouthafrica.co.za
http://www.southafricaiscrap.blogspot.com
http://deathofjohannesburg.blogspot.com
http://www.wea.co.za/