White Point & Black Point

F
Posted By
frankg
Oct 17, 2005
Views
350
Replies
4
Status
Closed
I’ve been asked for some stock images, and for them to be scanned with a White point of less than 252 and a Black point no less than 3. This keeps the rgb values slightly less than the full 256 range, and helps limit extreme values that will not print. And it helps limit errors when values fall outside the boundaries of an 8 bit file.
However, I have some files that are already scanned and saved as 16 bit. I do not want to have to go back and scan again, so how do I accomplish the same in PS?
Do I go to Levels and move the bottom Output Levels slider in at both ends by 3 points?
And if so, is this only true for files which have the Levels histogram showing
that the values touch the end on one or on both sides ? If they dont touch the
end then they’re less than the maximum/extreme of 0 & 256 anyway – correct?

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N
nomail
Oct 17, 2005
frankg wrote:

I’ve been asked for some stock images, and for them to be scanned with a White point of less than 252 and a Black point no less than 3. This keeps the rgb values slightly less than the full 256 range, and helps limit extreme values that will not print. And it helps limit errors when values fall outside the boundaries of an 8 bit file.
However, I have some files that are already scanned and saved as 16 bit. I do not want to have to go back and scan again, so how do I accomplish the same in PS?
Do I go to Levels and move the bottom Output Levels slider in at both ends by 3 points?

You can do that, but if one or both ends are clipped, it only means you push the clipped values inwards. It doesn’t give you back the detail that was clipped.

And if so, is this only true for files which have the Levels histogram showing that the values touch the end on one or on both sides ? If they dont touch the end then they’re less than the maximum/extreme of 0 & 256 anyway – correct?

Correct.

—
Johan W. Elzenga johan<<at>>johanfoto.nl Editor / Photographer http://www.johanfoto.nl/
F
frankg
Oct 17, 2005
I’ve been asked for some stock images, and for them to be scanned with a White point of less than 252 and a Black point no less than 3. This keeps the rgb values slightly less than the full 256 range, and helps
limit extreme values that will not print. And it helps limit errors when values fall outside the boundaries of an 8 bit file.
However, I have some files that are already scanned and saved as 16 bit. I
do not want to have to go back and scan again, so how do I accomplish the same in PS?
Do I go to Levels and move the bottom Output Levels slider in at both ends
by 3 points?

You can do that, but if one or both ends are clipped, it only means you push the clipped values inwards. It doesn’t give you back the detail that was clipped.

And if so, is this only true for files which have the Levels histogram showing that the values touch the end on one or on both sides ? If they dont touch the end then they’re less than the maximum/extreme of 0 & 256 anyway – correct?

Correct.
==============
if one or both ends are clipped, it only means you
push the clipped values inwards

but on Curves for example, if you grap the very top (highlight) of the line and drag it straight down, then you bring down that value, from 256 to whatever. And conversely for the black or bottom of the line
DD
Dave Du Plessis
Oct 17, 2005
On Mon, 17 Oct 2005 14:36:57 -0400, "frankg"
wrote:

if one or both ends are clipped, it only means you
push the clipped values inwards

but on Curves for example, if you grap the very top (highlight) of the line and drag it straight down, then you bring down that value, from 256 to whatever. And conversely for the black or bottom of the line

somebody recently said something of great value here (could have been tacit,and it sounded as if it was a relieve for the Kat as well); something to the effect that,* ìf the colours are not clipped*, and said points is not moved out of their corners, the colours can not be clipped via the curve dialog. Sometimes I lean heavy on this advice.

Dave
N
nomail
Oct 17, 2005
frankg wrote:

but on Curves for example, if you grap the very top (highlight) of the line and drag it straight down, then you bring down that value, from 256 to whatever. And conversely for the black or bottom of the line

Correct, but that is the same as using Levels, and also with the same restrictions.

—
Johan W. Elzenga johan<<at>>johanfoto.nl Editor / Photographer http://www.johanfoto.nl/

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