# Please answer reasonably -- What entities in a single stationaryimage of a B&W film's negative are m

Discussion in 'Australia Photography' started by GreenXenon, May 8, 2009.

1. ### GreenXenonGuest

Hi:

What entities -- excluding wavelength of light [or any EM radiation
for that matter] -- in a single stationary image of the negative of a
B&W film are measured in Hz?

What will the image look like if I downshift the frequencies of those
entities to 0.1 Hz?

Hz is commonly used to measure cycles-per-constant-time [usually in
seconds] but could also be used to measure cycles-per-constant-
distance [as in the cycles-per-meter in spatial frequency]. Right?

If a single stationary image is low-pass-filtered it will look duller.
If it is high-pass-filtered it will look sharper. This is an example
of frequency-processing in which Hz is *not* the reciprocal of the
period with respect to time.

In this case Hz measures the reciprocal of the period with respect to
distance. Right?

What other than spatial frequency would be measured in Hz in my above
scenario?

No offense but please respond with reasonable answers & keep out the
jokes, off-topic nonsense, taunts, insults, and trivializations. I am
really interested in this.

Thanks

GreenXenon, May 8, 2009

2. ### Dan MGuest

In this case Hz measures the reciprocal of the period with respect to
"Hertz" is, by definition, "cycles per second". If the frequency of
recurrence is measured for a unit of comparison other than 1 second of
elapsed time, Hertz cannot be used to expressed the measurement.

Dan M, May 8, 2009

3. ### GreenXenonGuest

http://en.wikipedia.org/wiki/Spatial_frequency

"In mathematics, physics, and engineering, spatial frequency is a
characteristic of any structure that is periodic across position in
space. The spatial frequency is a measure of how often the structure
repeats per unit of distance. The SI unit of spatial frequency is
cycles per meter."

GreenXenon, May 8, 2009
4. ### Scott DorseyGuest

Meters and seconds are not the same thing, no.
--scott

Scott Dorsey, May 8, 2009
5. ### J. ClarkeGuest

With light, spatial frequencies occur in the context of interference
patterns.

J. Clarke, May 9, 2009
6. ### GreenXenonGuest

Lets say there is a single stationary image black image with white
lines in it.

Higher spatial frequency = smaller lines, more lines in the image,
more lines per area in the image.

Lower spatial frequency = bigger lines, less lines in image, less
lines per area in image.

GreenXenon, May 9, 2009
7. ### GreenXenonGuest

Ok, lets say there is a single stationary image black image with white
lines in it.

Higher spatial frequency = smaller lines, more lines in the image,
more lines per area in the image.

Lower spatial frequency = bigger lines, less lines in image, less
lines per area in image.

GreenXenon, May 9, 2009

That's what you deserve for feeding the troll. I hope that headache
will last all weekend!

noyb

Don't feed the GreenTroll

noyb

10. ### Doug JewellGuest

So if I'm understanding your question, which doesn't make a
lot of sense, you are asking what would happen if the
spatial frequency on the piece of film was .1 cycles/metre?
(which you are incorrectly calling .1 Hz).

Well assuming that is what you are asking, one cycle would
require 10m of film.

Assuming that the intensity of the image changed from Dmin
to Dmax over the course of the cycle, the intensity at any
point along the piece of film would be:
Da=(Dmax+Dmin)/2 + (Dmax-Dmin)(sin a)/2
Where a = the phase angle at that position
a (in degrees) = x (in mm) / 10,000mm * 360 deg.

The variation in brightness across the space of a 35mm film
would then be
dD=(Dmax-Dmin)((sin a)-(sin a+1.296))

The maximum variation would be at the points where the
waveform crosses the midpoint. At these points, in the space
of 36mm the density would vary by 2.2% of Dmax-Dmin.

Therefore for a "waveform" with a cycle of .1 cycles/metre,
the maximum variation across the space of a single frame of
35mm film is so small that it would be barely noticeable.

Doug Jewell, May 9, 2009
11. ### Mr.TGuest

"Doug Jewell" <
Vain hope I'm afraid.

MrT.

Mr.T, May 10, 2009