What exactly is black point compensation?

It means that black in the source image's color space will be mapped to
black in the destination color space.

For example, because of paper reflectivity, a printed black is typically
brighter than black
on a monitor. Instead of converting printed black to something like
RGB(10,10,10) value, black will be converted to the black of the destination
color space, RGB(0,0,0).

--
Mike Russell
www.curvemeister.com/forum/

My View

2006-07-22 02:33:57 UTC

Thanks Russell

Post by Mike Russell
It means that black in the source image's color space will be mapped to
black in the destination color space.
For example, because of paper reflectivity, a printed black is typically
brighter than black
on a monitor. Instead of converting printed black to something like
RGB(10,10,10) value, black will be converted to the black of the
destination color space, RGB(0,0,0).
--
Mike Russell
www.curvemeister.com/forum/

Dave

2006-07-22 16:04:24 UTC

Post by My View
Thanks Russell

Pity you answered this stupid fool, Mike.
Maybe we should have a kind of houserule here
like only reacting to calls placed by people with names.
Sorry for this explosion, but you carry this kind of weight here,
that it irritates when a *nobody* does not even have the decency
of saying thanks to you by your name but calling you by the surname.

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/

Mike Russell

2006-07-22 16:14:03 UTC

Post by Dave
Pity you answered this stupid fool, Mike.
Maybe we should have a kind of houserule here
like only reacting to calls placed by people with names.
Sorry for this explosion, but you carry this kind of weight here,
that it irritates when a *nobody* does not even have the decency
of saying thanks to you by your name but calling you by the surname.

No offense taken for thanks of any kind. At least he spelled it with two
l's! :-)

--
Mike Russell
www.curvemeister.com/forum/

My View

2006-07-22 22:55:41 UTC

That time of the month Dave? I hope I spelt that correctly.

Thanks anyway Dave for pointing that out. I'm sure your heart is in the
right place.

My apologies Mike for quickly replying with your surname - honest mistake.

Don't you hate it when people are human and make honest mistakes.

Mike, your reply was exactly what I wanted to know as I tried Googling it
and all I got was a list of sites that explained how to print from PS with
"Black Point Compensation" selected. They did not state what BPC was - now I
know. I get all my prints done at professional labs and have never used the
PS print option. Simple printing at home is done using the printer software.
Hence my lack of knowledge on this particular subject.

I've received many great replies from you and always take your replies as an
excellent source to learn the finer points of PS.

I once again appreciate you realising that the main reason people use
newsgroups is because firstly they don't know or cannot find the exact
answer to a simple or complex question and secondly because they are looking
toward people like yourself to progressively improve their
knowledge in the use of this great package.

Mike once again keep up the great work - I always look for your name in
replies to this newsgroup as a source of good and reliable knowledge on
these subjects. Your website is on my favourites as well.

I hope you will continue to reply to "stupid fools" like myself so one day
we will all be as proficient in PS as Dave is.

Dave, I will also be looking out for your replies in the future so I can
make my own judgement as to whether or not you are also worth following like
Mike.

regards

Peter

Post by My View
Thanks Russell

Pity you answered this stupid fool, Mike.
Maybe we should have a kind of houserule here
like only reacting to calls placed by people with names.
Sorry for this explosion, but you carry this kind of weight here,
that it irritates when a *nobody* does not even have the decency
of saying thanks to you by your name but calling you by the surname.
Dave
Here are the links to those much-talked-about
http://www.crimexposouthafrica.co.za
http://www.southafricaiscrap.blogspot.com
http://deathofjohannesburg.blogspot.com
http://www.wea.co.za/

Dave

2006-07-23 12:38:51 UTC

Post by My View
That time of the month Dave? I hope I spelt that correctly.
Thanks anyway Dave for pointing that out. I'm sure your heart is in the
right place.

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.

Post by My View
Dave, I will also be looking out for your replies in the future so I can
make my own judgement as to whether or not you are also worth following like
Mike.

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.

Post by My View
regards
Peter

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/

KatWoman

2006-07-23 19:30:43 UTC

Post by My View
That time of the month Dave? I hope I spelt that correctly.
Thanks anyway Dave for pointing that out. I'm sure your heart is in the
right place.

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.

Post by My View
Dave, I will also be looking out for your replies in the future so I can
make my own judgement as to whether or not you are also worth following like
Mike.

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.

Post by My View
regards
Peter

Keep well,
Dave

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..

Dave

2006-07-23 20:24:33 UTC

On Sun, 23 Jul 2006 15:30:43 -0400, "KatWoman"

Post by My View
That time of the month Dave? I hope I spelt that correctly.
Thanks anyway Dave for pointing that out. I'm sure your heart is in the
right place.

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.

Post by My View
Dave, I will also be looking out for your replies in the future so I can
make my own judgement as to whether or not you are also worth following like
Mike.

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.

Post by My View
regards
Peter

Keep well,
Dave

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..

lol...!!! You did not miss the name I suggested, Katwoman.... surely
you didn't miss it :-O

Dave

KatWoman

2006-07-24 20:46:09 UTC

Post by Dave
On Sun, 23 Jul 2006 15:30:43 -0400, "KatWoman"

Post by My View
That time of the month Dave? I hope I spelt that correctly.
Thanks anyway Dave for pointing that out. I'm sure your heart is in the
right place.

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.

Post by My View
Dave, I will also be looking out for your replies in the future so I can
make my own judgement as to whether or not you are also worth following like
Mike.

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.

Post by My View
regards
Peter

Keep well,
Dave

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..

lol...!!! You did not miss the name I suggested, Katwoman.... surely
you didn't miss it :-O
Dave

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..

Sari

2006-07-25 20:35:34 UTC

On Mon, 24 Jul 2006 16:46:09 -0400, "KatWoman"

Post by Dave
On Sun, 23 Jul 2006 15:30:43 -0400, "KatWoman"

Post by My View
That time of the month Dave? I hope I spelt that correctly.
Thanks anyway Dave for pointing that out. I'm sure your heart is in the
right place.

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.

Post by My View
Dave, I will also be looking out for your replies in the future so I can
make my own judgement as to whether or not you are also worth following like
Mike.

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.

Post by My View
regards
Peter

Keep well,
Dave

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..

lol...!!! You did not miss the name I suggested, Katwoman.... surely
you didn't miss it :-O
Dave

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..

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...

KatWoman

2006-07-27 20:59:04 UTC

Post by Sari
On Mon, 24 Jul 2006 16:46:09 -0400, "KatWoman"

Post by Dave
On Sun, 23 Jul 2006 15:30:43 -0400, "KatWoman"

Post by My View
That time of the month Dave? I hope I spelt that correctly.
Thanks anyway Dave for pointing that out. I'm sure your heart is in the
right place.

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.

Post by My View
Dave, I will also be looking out for your replies in the future so I can
make my own judgement as to whether or not you are also worth
following
like
Mike.

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.

Post by My View
regards
Peter

Keep well,
Dave

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..

lol...!!! You did not miss the name I suggested, Katwoman.... surely
you didn't miss it :-O
Dave

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..

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..

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.

Dave

2006-07-23 14:14:50 UTC

Post by My View
That time of the month Dave? I hope I spelt that correctly.
Thanks anyway Dave for pointing that out. I'm sure your heart is in the
right place.

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.

Post by My View
Dave, I will also be looking out for your replies in the future so I can
make my own judgement as to whether or not you are also worth following like
Mike.

Post by My View
regards
Peter

BobLake

2006-07-25 15:38:27 UTC

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.

Post by My View
Thanks Russell

Pity you answered this stupid fool, Mike.
Maybe we should have a kind of houserule here
like only reacting to calls placed by people with names.
Sorry for this explosion, but you carry this kind of weight here,
that it irritates when a *nobody* does not even have the decency
of saying thanks to you by your name but calling you by the surname.
Dave
Here are the links to those much-talked-about
http://www.crimexposouthafrica.co.za
http://www.southafricaiscrap.blogspot.com
http://deathofjohannesburg.blogspot.com
http://www.wea.co.za/

Timo Autiokari

2006-07-23 07:10:27 UTC

Post by Mike Russell
It means that black in the source image's color space
will be mapped to black in the destination color space.

That is correct.

BPC is a proprietary color management addition to the ICC
color-management. It can be (but not always is) useful when profiles
that conform with v.2 ICC spec are being used since the blackpoint is
not properly managed in them. The v.4 ICC spec does specify device the
device blackpoint unambiguously so the effect of the BPC could be
(usually is) different when v.4 profiles are in use.

Also the v.2 ICC profiles can affect to the conversion of the device
blackpoint but this goes by approximation (where the v.4 profiles
provides the accurate blackpoint tag). Some/many profilers (that output
v.2 profiles) do such approximation, some do not. Therefore it is a very
good idea to check behavior of a new printing path, in respect to the
BPC, using a suitable test chart.

The problem with v.4 ICC profiling is that most of the
spectrophotometers are not good enough to measure the blackpoint
accurately, only the most expensive laboratory grade spectros have good
enough dynamic range.

Timo Autiokari
http://www.aim-dtp.net

e***@att.net

2006-07-23 14:19:15 UTC

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?

Post by Timo Autiokari

Post by Mike Russell
It means that black in the source image's color space
will be mapped to black in the destination color space.

That is correct.
BPC is a proprietary color management addition to the ICC
color-management. It can be (but not always is) useful when profiles
that conform with v.2 ICC spec are being used since the blackpoint is
not properly managed in them. The v.4 ICC spec does specify device the
device blackpoint unambiguously so the effect of the BPC could be
(usually is) different when v.4 profiles are in use.
Also the v.2 ICC profiles can affect to the conversion of the device
blackpoint but this goes by approximation (where the v.4 profiles
provides the accurate blackpoint tag). Some/many profilers (that output
v.2 profiles) do such approximation, some do not. Therefore it is a very
good idea to check behavior of a new printing path, in respect to the
BPC, using a suitable test chart.
The problem with v.4 ICC profiling is that most of the
spectrophotometers are not good enough to measure the blackpoint
accurately, only the most expensive laboratory grade spectros have good
enough dynamic range.
Timo Autiokari
http://www.aim-dtp.net

Timo Autiokari

2006-07-24 14:57:20 UTC

Post by e***@att.net
Should BPC make any observable difference to the mere mortals?

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

Mohamed Al-Dabbagh

2006-07-23 08:46:05 UTC