Well that's what standards bodies are for, you know ISO, DIN, IEEE.
At 05:42 PM 1/17/2002 +0100, Ramio wrote:
>Yes, it is. Where do you find your points and lines made of points to
>measure your lpm? In real world the edges of lines are not sharply defined
>if you look close enough - but I see you point: if you set limits you can
>measure lpm - but if you set a different limit, the result will be different.
>All the best!
>Raimo
>Personal photography homepage at
>http://personal.inet.fi/private/raimo.korhonen
>
>-----Alkuper�inen viesti-----
>L�hett�j�: Bob Blakely <[EMAIL PROTECTED]>
>Vastaanottaja: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
>P�iv�: 16. tammikuuta 2002 22:51
>Aihe: Re: And did I mention wrong
>
>
> >No, it is not effectively MTF. In fact, lpm is not a transfer function. In
> >fact, being a single point, it does not meet the mathematical definition of
> >a function!
> >
> >Further, absolute black is available in nature. I did *NOT* claim that
> >absolute black exists or is necessary, but it exists. Stop into an Afghan
> >terrorist cave, have an F-14 seal it up with a missile, and you will
> >"discover" absolute black in the visual spectrum.
> >
> >Further, no mythical absolute white is necessary to measure lpm *NOR* did I
> >claim that it exists. I have no idea where you came up with this nonsense.
> >
> >All that is necessary for the measurement is that the power in the white be
> >significantly higher that the power in the "black". This is why there is a
> >reference to 3 dB or half power in what I said. This is a _relative_
> >_power_, relative to the peak power in the white. How high is significantly
> >higher? well, that depends on how accurate you want the measurement. Just 15
> >dB or 5 stops is certainly enough.
> >
> >Measurement of MTF is subject to analogous constraints.
> >
> >Regards,
> >Bob...
> >
> >From: "Raimo Korhonen" <[EMAIL PROTECTED]>
> >
> >
> >> No - I am not wrong - when it is done the way you say, it is effectively
> >MTF. There is no absolute black or white in the nature, or in the world if
> >you will.
> >
> >> L�hett�j�: Bob Blakely <[EMAIL PROTECTED]>
> >>
> >> >No. You are wrong. Lines Per Millimeter is objective. It's often read
> >with
> >> >the human eye, but can be read by instruments. Lines Per Millimeter can
> >also
> >> >be calculated mathematically from the rise from black to white of a
> >single
> >> >edge (or fall from white to black). It is identical to the concept of
> >> >measuring the resolution of a radar (in this case the measure is
> >degrees).
> >> >Generally, the figure is not measured but calculated from the parameters
> >of
> >> >the antenna of which gain is the greatest determining factor. The edge of
> >> >resolution is where (for example) the light (from white to black) falls
> >off
> >> >by 3 dB or half power. It's at this point that two separate objects
> >cannot
> >> >be separated mathematically, let alone visually. For photo surveyors and
> >> >aircraft/spacecraft spies, this is the ONLY measure that counts. FYI, lpm
> >> >for these lenses are not measured by eye but by instruments. Stay tuned
> >for
> >> >an installment on how contrast affects this number.
> >> >
> >> >I do err, but not often and not in areas where I have worked.
> >> >
> >> >Regards,
> >> >Bob...
> >> >
> >> >From: "Raimo Korhonen" <[EMAIL PROTECTED]>
> >> >
> >> >
> >> >> Nope - lpm is measured by human eye and it is quite subjective. I think
> >> >that MTF is the most objective method, it takes into account both
> >contrast
> >> >and sharpness objectively.
> >> >> All the best!
> >> >> Raimo
> >> >> Personal photography homepage at
> >> >http://personal.inet.fi/private/raimo.korhonen
> >> >>
> >> >> L�hett�j�: Bob Blakely <[EMAIL PROTECTED]>
> >> >>
> >> >> >"Sharpness" and resolution are closely tied together, so I will
> >discuss
> >> >them both.
> >> >> >
> >> >> >Resolution is objective and quantifiable. It is a measure of the
> >ability
> >> >to separate two
> >> >> >identical objects as they are brought close together. In photography,
> >> >this is measured in
> >> >> >lines per millimeter where the lines are black the spaces between the
> >> >lines are white.
> >> >> <snip>
> >> >> >Regards,
> >> >> >Bob...
> >> -
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> >-
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