Re: filmscanners: Vuescan grain removal idea

["Maris V. Lidaka, Sr." <mlidaka@ameritech.net>]

Good work, Dean.

Maris

----- Original Message -----
From: "Shough, Dean" <dean.shough@lmco.com>
To: <filmscanners@halftone.co.uk>
Sent: Tuesday, March 20, 2001 12:23 PM
Subject: RE: filmscanners: Vuescan grain removal idea


| > Maybe Ed or someone else has a better idea about how the Vuescan grain
| > removal option could be expanded and in a practical sense work even
| > better.
| > If you do then please give us your input.
| >
|
| I don't know about VueScan, but I did read through US Patent 5,673,336
which
| seems to be the basis for ROC and  probably lead to the idea for GEM.  One
| of the inventors is Albert Edgar, now with Applied Science Fiction.  The
| basic idea in the patent is that the grain in each layer of color film is
| independent of the other layers.  Thus the grain noise in each color layer
| is independent of the grain noise in the other layers.  This agrees with
| your observation that the grain noise shows up a multi colored noise.
|
| A more technical excerpt of the patent follows:
|
| " ... the present invention corrects for the interaction for the dye
layers
| in the film and the scanner spectral sensitivity as well as correcting for
| the changes in the dye layers in the film with aging.
|
| "The invention is based on the observation that as each dye layer is
| deposited separately in the film, one would expect that the "noise" from
the
| grain boundaries in one layer to be independent from the "noise" due to
the
| grain boundaries in other layers.  If there is correlation in the noise
| between color scans, it is because the scanner is measuring the grain
| boundaries in more than one layer in the color scan.
|
| "To measure the noise, the image and noise must be separated...
|
| "The infrared scan is used to detect imperfections in the film medium
| itself.  As discussed in ... US Pat No, 5,266,805 ...  Unfortunately, in
the
| infrared scan, there can be cross talk from the red sensitive, cyan
forming
| layer which would be identified as defects.  The present invention can be
| used to correct for the red crosstalk in the infrared scan.
|
| "FIG. 5 shows the process by which the correlated noise is separated from
| the scanned image.
|
| "Once the invention has removed the effects (sic) to dye color changes and
| retrieved the pure separate color images, the effects of aging from the
pure
| separate color images can be removed using the changes common to black and
| white images in particular contrast stretch between black and white points
| in the images.  It should be emphasized that applying this contrast
stretch
| works well only after the invention has separated the color records.
|
| "There is virtually nothing above about 40 line pairs per millimeter
spatial
| frequency recorded with today's lenses and film from real world images.
| This cutoff corresponds to a 2000 by 3000 pixel scan of 35 millimeter
film.
| Conversely, the grain noise begins with  flat spectrum and is attenuated
| only at very high frequencies by grain size and dye diffusion as discussed
| above, which have an effect above 100 line pairs per millimeter.
|
| "A practical solution first isolates frequencies around 40 line pairs to
| eliminate those parts of the image in which the energy seen at these high
| frequencies is predominately from grain noise, and prunes out or
emphasizes
| those where the high frequencies also contains image detail.  For example,
a
| sky, a blurred background, ...  Because the noise is a constant across the
| image, a region that contains more high frequencies than elsewhere in the
| image is more active because o image detail...
|
|