[filmscanners] Re: HP PhotsSmart - questions

["Arthur Entlich" <artistik@shaw.ca>]

Here is a triline CCD sensor:

RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG
BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB

If I have counted correctly, this CCD has 50 sensors for each color.

In my example, as the film moves and is projected onto the sensor CCD,
the stepper motor stops 75 times to complete one 35mm frame, and a
snapshot (sample) is taken by each sensor, each time it stops.  Since
the film is 1.5 times longer than wide, that means a total of 50 sensors
wide (projected onto them by a 1" wide film) by 50 stops per inch (75
divided by 1.5), or a 50 x 50 ppi image is created, having a pixel
dimension of 50 pixels by 75 pixels.

The total number of pixels of the frame will be 50 pixels wide by 75
pixels (or sampling points) long for each color, one R matrix, or G
matrix, one B matrix.

Since the sensor lines are actually not all in the exact same location
(see triline sensor above again) and how could they be? there is an
offset in one axis which is corrected for in software so that the three
color separations are placed into registration when creating the final
image.

The number of discrete sensors within a specific CCD is always finite.
However, the number of steps the motors take, and therefore the number
of samples recorded by the CCD sensors in the other axis, can be more or
less than the finite sensor numbers across.

That is why you will have heard of scanner which claim "300 x 600 ppi"
native or optical resolution.  In that case, chances are the 300 ppi is
the density or number of sensors per inch relative to the original
source width, and the 600 is the number of times the film/print or
sensor bar stopped and took a sample.

Although it only provides more information in one direction (axis) it
still does produce a more accurate scan.

Art



Laurie Solomon wrote:

> I guess my confusion revolves around my not understanding what "three
> stripes" and "2400 photo sites" means and refers to.
> Does 2400 photo sites refer to 2400 samples, 2400 pixels, or something
> else?  Does three stripes refer to the three colors in RGB or three
> horizontal lines of sensors to capture the incoming data information in
> the form of the imported light values or something else?
>
>
> ----Original Message----
> From: filmscanners_owner@halftone.co.uk
> [mailto:filmscanners_owner@halftone.co.uk] On Behalf Of
> wbgilloolyjr@charter.net
> Sent: Monday, August 08, 2005 5:10 PM
> To: laurie@advancenet.net
> Subject: [filmscanners] Re: HP PhotsSmart - questions
>
>
>>His scanner may have 3 CCD's, the old Agfa Horizon had 5.
>>
>>Mr. Bill
>>
>>
>>Laurie Solomon wrote:
>>
>>> Bob,
>>>
>>>First, thanks for the information; but second, please elaborate.  I
>>>do not understand what is meant by "There are, in fact, three
>>>stripes. Each having greater than 2400 photo sites" in the quote:
>>
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>
>
>

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