Steps From Levels?

Wilba wrote:

Forget the original. Put it this way - in the image itself as it is, if a
pixel has the value r, g, b, can I determine the RGB values for one step up
or down from that?

Only if more is known. For example how the RGB values are
translated --- linear, gamma, monitor proofed? Or are they
printed on paper with a (simple case) pure black-and-white (*not*
grayscale, *no* dithering) printer, resulting in exactly black
and white, where it depends on how black the black ink is, how
much is sprayed/painted/transferred onto the paper, how white the
paper is (is it greyish recycling paper or a superwhite one with
optical brighteners?) etc.

Or maybe you are putting the image on transparent film via laser
writer and chemical development. Then it not only depends on how
transparent and how black the film can be made, but also on how
bright the projection lamp is and how reflective the projection
screen will be.

Maybe you are viewing it on a monitor. Is that a flatscreen
or a good old CRT display? If it's a flatscreen, at what angle
are you looking at it? Is the environment dark, or is it in the
bright sun, where the same reflects in the monitor and renders
even pure black and white near identical and maybe a quarter stop
apart from each other, if you are lucky?

Say, you could be developing the photos --- what graduation
will you use with the paper? Rather soft (so everything's more
grayish and 2 given RGB values are usually closer to each other
in luminosity) or rather hard (so things seem crisper, but details
can be lost in the shadows (everything pure black) and highlights
(everything pure white) and 2 given RGB values might be identical
or further from each other in luminosity)?


And of course, each medium will have different distances
between black and white, and hence different answers for 'one
stop more' ...

-Wolfgang

Wolfgang Weisselberg wrote:
Wilba wrote:

Forget the original. Put it this way - in the image itself as it is, if a
pixel has the value r, g, b, can I determine the RGB values for
one step up or down from that?

Only if more is known. For example how the RGB values are
translated --- linear, gamma, monitor proofed?

Windows, gamma 2.2, sRGB, on a CRT calibrated under ambient light from an
open south-facing window (in the southern hemisphere). And I'm wearing light
grey underpants. :- )

The curve given by the Matlab equation on Norman Koren's Simplified Zone
System page (http://www.normankoren.com/zonesystem.html) give me everything
I want. The levels it gives for the zones are 0, 31, 55, 86, 126, 170, 212,
244, 255, and those tones look fine. (Contrast with the linear levels - 0,
32, 64, 96, 128, 160, 192, 224, 255. Here's a graphic that shows both sets -
http://www.users.on.net/~alanw/Usenet/ZoneSystem.gif.) It's easy enough to
work the maths to get an arbitrary offset from any level.

Wilba wrote:
Wolfgang Weisselberg wrote:
Wilba wrote:

Forget the original. Put it this way - in the image itself as it is, if a
pixel has the value r, g, b, can I determine the RGB values for
one step up or down from that?

Only if more is known. For example how the RGB values are
translated --- linear, gamma, monitor proofed?

Windows, gamma 2.2, sRGB, on a CRT calibrated under ambient light from an
open south-facing window (in the southern hemisphere). And I'm wearing light
grey underpants. :- )

You should try bleaching them. :-)

The curve given by the Matlab equation on Norman Koren's Simplified Zone
System page (http://www.normankoren.com/zonesystem.html) give me everything
I want. The levels it gives for the zones are 0, 31, 55, 86, 126, 170, 212,
244, 255, and those tones look fine.

OK, but why not 0, 55, 126, 212, 255? Why exactly 8 zones?
Does your monitor show exactly 2^8 times the luminance at 255
than at 0? Doesn't that change when the ambient light (which
adds the same amount to 0 and 255, but since 0 is near zero,
has great impact with 0 and much less with 255) changes, say,
from bright blue sky to dreary overcast to night?

-Wolfgang

Wolfgang Weisselberg wrote:
Wilba wrote:
Wolfgang Weisselberg wrote:
Wilba wrote:

Forget the original. Put it this way - in the image itself as it is, if
a
pixel has the value r, g, b, can I determine the RGB values for
one step up or down from that?

Only if more is known. For example how the RGB values are
translated --- linear, gamma, monitor proofed?

Windows, gamma 2.2, sRGB, on a CRT calibrated under ambient
light from an open south-facing window (in the southern hemisphere).
And I'm wearing light grey underpants. :- )

You should try bleaching them. :-)

I prefer Bart Simpson's idea.

The curve given by the Matlab equation on Norman Koren's Simplified
Zone System page (http://www.normankoren.com/zonesystem.html)
give me everything I want. The levels it gives for the zones are 0, 31,
55, 86, 126, 170, 212, 244, 255, and those tones look fine.

OK, but why not 0, 55, 126, 212, 255? Why exactly 8 zones?

See the "Zones" section at http://www.normankoren.com/zonesystem.html. "Each
zone represents a doubling or halving of the luminance" on a "properly
calibrated monitor". You'd have to ask someone like Norman if you want to
know more about that.

Does your monitor show exactly 2^8 times the luminance at 255
than at 0?

It doesn't matter what my monitor shows, since I'm measuring values from the
image data. Judgment by eye is not involved.

Doesn't that change when the ambient light (which
adds the same amount to 0 and 255, but since 0 is near zero,
has great impact with 0 and much less with 255) changes, say,
from bright blue sky to dreary overcast to night?

No. Monitor illumination is irrelevant to the values measured from the image
data, e.g. using the Info window in Photoshop.

All I want is a rough idea (a rule of thumb), about what the levels might be
like X steps from what's under the cursor. Or the other way around - roughly
how many steps are there between two points? That doesn't require laboratory
quality calibration and control of ambient illumination for every data
point.

Wilba wrote:
Wolfgang Weisselberg wrote:
Wilba wrote:
Wolfgang Weisselberg wrote:
Wilba wrote:

OK, but why not 0, 55, 126, 212, 255? Why exactly 8 zones?

See the "Zones" section at http://www.normankoren.com/zonesystem.html. "Each
zone represents a doubling or halving of the luminance" on a "properly
calibrated monitor". You'd have to ask someone like Norman if you want to
know more about that.

Does your monitor show exactly 2^8 times the luminance at 255
than at 0?

It doesn't matter what my monitor shows,

Norman says it matters, you just quoted him exactly on this!
Understand what you quote, it's important. :-)

since I'm measuring values from the
image data. Judgment by eye is not involved.

So it doesn't matter what your monitor shows, because you
don't look at your shots?

Doesn't that change when the ambient light (which
adds the same amount to 0 and 255, but since 0 is near zero,
has great impact with 0 and much less with 255) changes, say,
from bright blue sky to dreary overcast to night?

No. Monitor illumination is irrelevant to the values measured from the image
data, e.g. using the Info window in Photoshop.

Ah, you really don't look at your shots, (nor do you print them
or anything, they are just blobs of data!) and, in addition,
your monitor is not properly calibrated anyway, since it does
not exhibit the behaviour Norman says it should have for a
"properly calibrated monitor".

Why do you bother having a monitor at all, much less calibrating
it? A teletype (of the printer type) would do just as well for
looking at the data values!

All I want is a rough idea (a rule of thumb), about what the levels might be
like X steps from what's under the cursor.

2^X or 1/2^X times as bright in luminance. Easy.
As a phptographer you surely have developed an eye that can
roughly judge the contrast range in stops ...
(it's not st*e*ps, it's st*o*ps. As in "Waterhouse stop".)

Or the other way around - roughly
how many steps are there between two points?

One for each doubling or halving of luminance. Easy.

That doesn't require laboratory
quality calibration and control of ambient illumination for every data
point.

As a "rule of thumb" using just roughly ±30 on 8bit
gamma-2.2-encoded data works well enough, no need
to bother with formulas at all.

-Wolfgang

On Tue, 1 Sep 2009 01:04:06 +0200, Wolfgang Weisselberg
wrote:


Ah, you really don't look at your shots, (nor do you print them
or anything, they are just blobs of data!) and, in addition,
your monitor is not properly calibrated anyway, since it does
not exhibit the behaviour Norman says it should have for a
"properly calibrated monitor".

Why do you bother having a monitor at all, much less calibrating
it? A teletype (of the printer type) would do just as well for
looking at the data values!

You'll have to excuse this resident Wolfgang troll. He's not aware that the
data in the image file is independent of the luminosity displayed on a
monitor. He's trying to invent and guess ways that he might manipulate
people into nonsense arguments with him. A value of 127 for an R, G, or B
value in a file will read the same value in any good editor on anyone's
monitor. Though it might be represented to the eye in varying levels of
luminosity. This does not, however, change the value stored in the file and
it will be read the same with whatever "color picker" tool that you use to
read those values.

Wolfgang's not too bright, nor does he have any real experience with
photography and editors, though he desperately tries to sound like he knows
about these things. He reveals his troll's utter stupidity like this often,
if you read carefully enough.

Wolfgang Weisselberg wrote:
Wilba wrote:

[Snip heaps of irrelevant insolent trolling.]

All I want is a rough idea (a rule of thumb), about what the
levels might be like X steps from what's under the cursor.

2^X or 1/2^X times as bright in luminance. Easy.
As a phptographer you surely have developed an eye that can
roughly judge the contrast range in stops ...

As a PHP toe grapher? No. :- )

I'm not sure that I do have that ability at a good level. I'm sure I had
something like that in my monochrome wet darkroom days, but that's a long
time ago, and I doubt that I can do it accurately with colour images. And
without some objective measure, how would I know if I can?

(it's not st*e*ps, it's st*o*ps. As in "Waterhouse stop".)

Only apertures stop, and when one does it stops in steps, as does every
other way of changing exposure. Stop is an aperture-specific step, so
although it's conventional to do so, it's misleading to talk about stops of
shutter speed, ISO, or exposure compensation.

Or the other way around - roughly
how many steps are there between two points?

One for each doubling or halving of luminance. Easy.

It sounds easy until you want to measure it from the levels in an image, and
you don't know how to do that. That's where this thread started, and it's
the only point of it.

As a "rule of thumb" using just roughly ±30 on 8bit
gamma-2.2-encoded data works well enough, no need
to bother with formulas at all.

If you knew the answer all along, why didn't you just give it at an
appropriate time? :- )

32 levels represents a linear set of zones, and is not a bad approximation
up to about the third lightest zone. I don't intend to use the formula, but
it enabled me to produce the chart I posted
(http://www.users.on.net/~alanw/Usenet/ZoneSystem.gif), which is handy as a
ROT, and gives me a way to calibrate my eye. Hmm, I should do one with
colours ....

Troll Spotter wrote:
Wolfgang Weisselberg wrote:

Ah, you really don't look at your shots, (nor do you print them
or anything, they are just blobs of data!) and, in addition,
your monitor is not properly calibrated anyway, since it does
not exhibit the behaviour Norman says it should have for a
"properly calibrated monitor".

Why do you bother having a monitor at all, much less calibrating
it? A teletype (of the printer type) would do just as well for
looking at the data values!

You'll have to excuse this resident Wolfgang troll. He's not aware that
the
data in the image file is independent of the luminosity displayed on a
monitor. He's trying to invent and guess ways that he might manipulate
people into nonsense arguments with him. A value of 127 for an R, G, or B
value in a file will read the same value in any good editor on anyone's
monitor. Though it might be represented to the eye in varying levels of
luminosity. This does not, however, change the value stored in the file
and
it will be read the same with whatever "color picker" tool that you use to
read those values.

Wolfgang's not too bright, nor does he have any real experience with
photography and editors, though he desperately tries to sound like he
knows about these things. He reveals his troll's utter stupidity like this
often, if you read carefully enough.

Thanks. I worked out Wolfy as soon as he appeared here. It's fun to taunt
him occasionally. But it has been beneficial for me to think through some of
the sensible ideas that his nonsense brings to mind.

Troll Spotter wrote:
On Tue, 1 Sep 2009 01:04:06 +0200, Wolfgang Weisselberg

You'll have to excuse this resident Wolfgang troll.

Troll spotted! "Troll spotter" is a resident troll that does
nothing than denounce regulars as trolls.

He's not aware that the
data in the image file is independent of the luminosity displayed on a
monitor.

For an idiot you are doing badly with your guessing.

He's trying to invent and guess ways that he might manipulate
people into nonsense arguments with him. A value of 127 for an R, G, or B
value in a file will read the same value in any good editor on anyone's
monitor.

Even if the monitor is broken, powerless, disconnected *and*
switched off. As I said, for an idiot ...

Though it might be represented to the eye in varying levels of
luminosity. This does not, however, change the value stored in the file and
it will be read the same with whatever "color picker" tool that you use to
read those values.

Obviously, a value of 127 for R, G, or B will show up as 0 or 1
or maybe 2, once it is translated from a 12 bit RAW to 8bit sRGB.
As I said, for an idiot ...

Wolfgang's not too bright, nor does he have any real experience with
photography and editors, though he desperately tries to sound like he knows
about these things. He reveals his troll's utter stupidity like this often,
if you read carefully enough.

It only appears so to trolls and idiots. Thinking people can
follow my arguments. Well, what did you expect?

-Wolfgang

Wilba wrote:
Wolfgang Weisselberg wrote:
Wilba wrote:

[Snip heaps of irrelevant insolent trolling.]

You forgot insubordination, King "goalpost shifter" Wilba.

All I want is a rough idea (a rule of thumb), about what the
levels might be like X steps from what's under the cursor.

2^X or 1/2^X times as bright in luminance. Easy.
As a phptographer you surely have developed an eye that can
roughly judge the contrast range in stops ...

I'm not sure that I do have that ability at a good level. I'm sure I had
something like that in my monochrome wet darkroom days, but that's a long
time ago, and I doubt that I can do it accurately with colour images.

Then you should relearn it.

And without some objective measure, how would I know if I can?

You happen to have a camera, probably with a center or spot mode.
It can be used as a light meter with enough accuracy for that task.

(it's not st*e*ps, it's st*o*ps. As in "Waterhouse stop".)

Only apertures stop, and when one does it stops in steps,

Stepless aperture systems have long been invented. Look at
your eye.

as does every
other way of changing exposure.

Stepless exposure times also have been invented. In fact,
the old method of a hat over the lens is stepless.

Stop is an aperture-specific step, so
although it's conventional to do so, it's misleading to talk about stops of
shutter speed, ISO, or exposure compensation.

If you say so. Source? Or is that just your personal opinion?


Or the other way around - roughly
how many steps are there between two points?

One for each doubling or halving of luminance. Easy.

It sounds easy until you want to measure it from the levels in an image, and
you don't know how to do that. That's where this thread started, and it's
the only point of it.

You point your light meter to the parts of the image.

As a "rule of thumb" using just roughly ±30 on 8bit
gamma-2.2-encoded data works well enough, no need
to bother with formulas at all.

If you knew the answer all along, why didn't you just give it at an
appropriate time? :- )

Because you wanted to measure, nothing about roughly --- and my
point still stands: will your image in it's later representation
have 8 stops of range? Can your prints even deliver 8 ranges?

So what is the difference between 0 and 255 in the *final*
represenation of the image?

-Wolfgang