Resolution of photo paper?

In article , Alfred Molon
writes
David Littlewood wrote:

Note however that 60-70 lp/mm is way in excess of what the keenest human
eye can detect; that limit is closer to 30 lp/mm.

Can a human detect 30 line pairs/mm without using a loupe (or a
microscope) ?

Not directly in terms of resolution. However, the edge acutance and the
tonal quality of the print improves up to this figure in a way that can
be detected with the naked eye.

Think of it this way - on a print at arm's length your eye can resolve
about 10 lp/mm (assuming good eyesight and a high contrast print).
Anything finer than this is simply not recognised as separate lines.
However, there is a strong perceived difference in the quality of the
lines you can see at 10 lp/mm according to whether they are at the
resolution limit (think sine wave cross section) or well short of it
(think square wave). The eye can see whether the lines have sharp edges.
Experimentation suggests that the improvement becomes undetectable by a
total resolution at the paper of about 30 lp/mm - IOW, a 3x factor is
enough to convert the 10 lp/mm sine wave into a fairly good 10 lp/mm
square wave.

These figures come from the work of testers far more rigorous than
anything I have done. However, my own (crude) tests have satisfied me
that if I move away from a pair of test charts, one razor sharp (square
wave) and one fuzzy (sine wave), I can clearly resolve the sharp set to
finer lp/mm limit than I can for the fuzzy ones from the same distance.
The fuzzy ones go "muddy" and grey sooner. I guess that is saying the
same thing a different way round. This is the edge acutance effect, and
it needs "oversampling" to work.

Its not unrelated to the fact that for a digital audio signal to sound
"right" it must be sampled at a frequency (IIRC, 48 kHz) about 3x that
which is the top limit of human hearing (varies with age, but say 16
kHz).

David
--
David Littlewood

In article , Alfred Molon
writes
David Littlewood wrote:

Note however that 60-70 lp/mm is way in excess of what the keenest human
eye can detect; that limit is closer to 30 lp/mm.

Can a human detect 30 line pairs/mm without using a loupe (or a
microscope) ?

Not directly in terms of resolution. However, the edge acutance and the
tonal quality of the print improves up to this figure in a way that can
be detected with the naked eye.

Think of it this way - on a print at arm's length your eye can resolve
about 10 lp/mm (assuming good eyesight and a high contrast print).
Anything finer than this is simply not recognised as separate lines.
However, there is a strong perceived difference in the quality of the
lines you can see at 10 lp/mm according to whether they are at the
resolution limit (think sine wave cross section) or well short of it
(think square wave). The eye can see whether the lines have sharp edges.
Experimentation suggests that the improvement becomes undetectable by a
total resolution at the paper of about 30 lp/mm - IOW, a 3x factor is
enough to convert the 10 lp/mm sine wave into a fairly good 10 lp/mm
square wave.

These figures come from the work of testers far more rigorous than
anything I have done. However, my own (crude) tests have satisfied me
that if I move away from a pair of test charts, one razor sharp (square
wave) and one fuzzy (sine wave), I can clearly resolve the sharp set to
finer lp/mm limit than I can for the fuzzy ones from the same distance.
The fuzzy ones go "muddy" and grey sooner. I guess that is saying the
same thing a different way round. This is the edge acutance effect, and
it needs "oversampling" to work.

Its not unrelated to the fact that for a digital audio signal to sound
"right" it must be sampled at a frequency (IIRC, 48 kHz) about 3x that
which is the top limit of human hearing (varies with age, but say 16
kHz).

David
--
David Littlewood

David Littlewood wrote in
:

Its not unrelated to the fact that for a digital audio signal to sound
"right" it must be sampled at a frequency (IIRC, 48 kHz) about 3x that
which is the top limit of human hearing (varies with age, but say 16
kHz).

Actually it is unrelated The 48 or 44 KHz comes from the fact
that the sampling frequency must be larger than 2x20 KHZ with a
margin for how easy it is to make low pass filters.


/Roland

Alfred Molon writes:

Can a human detect 30 line pairs/mm without using a loupe (or a
microscope) ?

Depends on how close they are, which depends on how nearsighted they
are! The human eye can see 60 cycles (line pairs) per degree of arc.
This is equal to 30 lp/mm at a distance of 115 mm or 4.5 inches.

But for practical purposes, somewhere in the range 4-8 lp/mm is
considered a sharp print.

Dave

In article , Roland Karlsson
writes
David Littlewood wrote in
:

Its not unrelated to the fact that for a digital audio signal to sound
"right" it must be sampled at a frequency (IIRC, 48 kHz) about 3x that
which is the top limit of human hearing (varies with age, but say 16
kHz).

Actually it is unrelated The 48 or 44 KHz comes from the fact
that the sampling frequency must be larger than 2x20 KHZ with a
margin for how easy it is to make low pass filters.


/Roland

Roland, your subsequent words in no way prove the initial assertion. I
was simply pointing out an analogy, not a direct equivalence. If you
wish to make a sensible comment please do so. Otherwise.....

David
--
David Littlewood

In article , Roland Karlsson
writes
David Littlewood wrote in
:

Its not unrelated to the fact that for a digital audio signal to sound
"right" it must be sampled at a frequency (IIRC, 48 kHz) about 3x that
which is the top limit of human hearing (varies with age, but say 16
kHz).

Actually it is unrelated The 48 or 44 KHz comes from the fact
that the sampling frequency must be larger than 2x20 KHZ with a
margin for how easy it is to make low pass filters.


/Roland

Roland, your subsequent words in no way prove the initial assertion. I
was simply pointing out an analogy, not a direct equivalence. If you
wish to make a sensible comment please do so. Otherwise.....

David
--
David Littlewood

In article , Dave Martindale
writes
Alfred Molon writes:

Can a human detect 30 line pairs/mm without using a loupe (or a
microscope) ?

Depends on how close they are, which depends on how nearsighted they
are! The human eye can see 60 cycles (line pairs) per degree of arc.
This is equal to 30 lp/mm at a distance of 115 mm or 4.5 inches.

But for practical purposes, somewhere in the range 4-8 lp/mm is
considered a sharp print.

Dave

Only by those who have never seen an actual sharp print.
--
David Littlewood

In article , Dave Martindale
writes
Alfred Molon writes:

Can a human detect 30 line pairs/mm without using a loupe (or a
microscope) ?

Depends on how close they are, which depends on how nearsighted they
are! The human eye can see 60 cycles (line pairs) per degree of arc.
This is equal to 30 lp/mm at a distance of 115 mm or 4.5 inches.

But for practical purposes, somewhere in the range 4-8 lp/mm is
considered a sharp print.

Dave

Only by those who have never seen an actual sharp print.
--
David Littlewood

David Littlewood wrote in
:

Roland, your subsequent words in no way prove the initial assertion. I
was simply pointing out an analogy, not a direct equivalence. If you
wish to make a sensible comment please do so. Otherwise.....


Sorry David ... the two things are 100% unrelated. There is no
analogy at all. It is quite the oposite. In one case you resolve
less than half the sampling frequency. In the other case you
claim that you can actually "detect" three times more than the
resolving power. "More" and "less" are the oposites. 2 and 3 are
not the same. So - your original claim has no meaning at all.
So - don't tell me to write sensible comments.


/Roland

David Littlewood wrote in
:

Roland, your subsequent words in no way prove the initial assertion. I
was simply pointing out an analogy, not a direct equivalence. If you
wish to make a sensible comment please do so. Otherwise.....


Sorry David ... the two things are 100% unrelated. There is no
analogy at all. It is quite the oposite. In one case you resolve
less than half the sampling frequency. In the other case you
claim that you can actually "detect" three times more than the
resolving power. "More" and "less" are the oposites. 2 and 3 are
not the same. So - your original claim has no meaning at all.
So - don't tell me to write sensible comments.


/Roland