Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2001-08-27
2004-02-24
Porta, David (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C358S475000, C358S509000
Reexamination Certificate
active
06696683
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image scanning apparatus for scanning an image on an original, a control program for controlling the same and a storage medium storing the control program.
2. Description of the Related Art
In an image scanning apparatus for acquiring a digital image by scanning an image on an original, a CCD photodetector has been heretofore used as a light receiving section of a scanning optical system for scanning the original. Herein, the original is a film, a printing original, and the like, and the image scanning apparatus is a so-called scanner.
FIG.
12
(
a
) is a diagram showing a photoelectric-conversion characteristic of the CCD photodetector, that is, a relation between an exposure and an intensity.
The intensity R indicated by an output signal of the CCD photodetector becomes higher as the exposure I of the CCD photodetector increases. However, when the exposure I exceeds a quantization exposure limit Ia, the intensity R saturates at a constant value Ra.
Furthermore, when the exposure I exceeds an exposure Ia′ slightly higher than the quantization exposure limit Ia, an “overflow” occurs.
Herein, the “overflow” signifies a phenomenon that charges are flown over the surroundings from a pixel in the CCD photodetector in which signal charges are to be held and an analog shift register in the CCD photodetector.
When this “overflow” occurs at any one of the plurality of pixels or at any one of the analog shift registers, a phenomenon called smear or blooming (hereinafter referred to as “overflow” phenomenon) occurs in an image finally obtained.
On the contrary, when the exposure I is insufficient, a dynamic range of the CCD photodetector is not effectively utilized, which deteriorates the SN ratio of an image signal and an overall quality of a finally obtained image.
Accordingly, in order to set an exposure condition that is proper (hereinafter referred to as a proper exposure condition), the conventional image scanning apparatus examines the intensity histogram of an image to be scanned before scanning it.
Herein, a pre-scan must be executed to examine the intensity histogram.
The pre-scan is a scanning performed under a predetermined exposure condition (specifically, an exposure condition in which an intensity does not saturate at scanning any image, that is, an exposure does not exceed a quantization exposure limit Ia in scanning any image.
Incidentally, the exposure condition is determined depending on a combination of a drive condition of an illumination optical system and a drive condition of a CCD photodetector, that is, a combination of a scanning light amount and a charge storage time. Accordingly, a predetermined exposure condition is set according to a predetermined scanning light amount and a predetermined charge storage time.
FIG.
12
(
b
) is a drawing for explaining an original. Descriptions are made in the following for the case where the original to be scanned is a negative film.
In each film, a position of an image frame (an area in which an image is stored)
12
a
on the film varies depending on sorts of cameras used for photographing.
Accordingly, a scanning area
12
E that is determined in advance in the image scanning apparatus has a range slightly wider than the image frame
12
a.
FIG.
12
(
c
) shows an intensity histogram that is acquired by a pre-scan.
The intensity histogram illustrates the intensity of the scanning area
12
E ranges from 0 to Rmax. This range corresponds to a part of the dynamic range of the CCD photodetector, which ranges from 0 to Ra.
The image scanning apparatus refers to the intensity Rmax of the brightest point in the scanning area
12
E (hereinafter to be referred to as “an absolute brightness point”).
The image scanning apparatus sets the exposure condition so that the dynamic range of the CCD photodetector is effectively utilized in the scan, and in addition the exposure by this absolute brightness point does not exceed the an exposure limit.
To be specific, the image scanning apparatus sets the exposure condition to have the exposure in the scan Ra/Rmax times as much as the exposure in the pre-scan.
The exposure condition newly set described above is a proper exposure condition in the conventional image scanning apparatus.
FIG.
12
(
d
) is an intensity histogram acquired by the scan.
This intensity histogram shows clearly that an intensity range of the scanning area
12
E after the scan is expanded to the whole area of the dynamic range of the CCD photodetector, which ranges from 0 to Ra.
As a result, the S/N ratio of an image signal is enhanced to the maximum within a range where the overflow phenomenon does not occur.
Incidentally, as described above the scanning area
12
E is set slightly wider than the image frame
12
a.
Accordingly, the scanning area
12
E includes not only the image frame
12
a
that is an effective picture but also a base
12
b
that is a non-effective picture.
Herein, the effective picture refers to a picture to be expressed in tones, and the non-effective picture refers to a picture which has a very high intensity compared to the effective picture and needs not to be expressed in tones.
Incidentally, the intensity histogram shown in FIG.
12
(
c
) and FIG.
13
(
a
) to be described later has two peaks.
Of these two peaks, the gentle peak on the low intensity side corresponds to intensity information of the image frame
12
a,
and the steep peak on the high intensity side corresponds to intensity information of the base
12
b.
Accordingly, the intensity Rmax at the absolute brightness point is equal to an intensity of the base
12
b.
Herein, if an object to be scanned is a comparatively bright image, an intensity in the intensity range of the image frame
12
a
is greatly lower than the intensity Rmax of the base
12
b,
as shown in FIG.
13
(
a
).
However, the foregoing proper exposure condition is determined in accordance with the intensity Rmax at the absolute brightness point (the intensity at the base
12
b
), which may be a cause of the overflow. The proper exposure condition should not be determined in accordance with the intensity at the brightest point (hereinafter referred to as “the brightest point of picture”) of the effective picture (image frame
12
a
).
Therefore, when the intensity range of the image frame
12
a
is significantly lower than the intensity Rmax of the base
12
b,
the intensity range allocated to the image frame
12
a
after the scan is still narrow as shown in FIG.
13
(
b
), even when the foregoing proper exposure condition is set.
In this case, it has to be permitted a situation that the S/N ratio of the image signal remains small.
Furthermore, such a problem may occur in positive films in addition to negative films.
Such a problem arises, especially, when images such as a starry sky and metal goods are objects of scanning.
This is because these images contain a luminescent point that is a non-effective picture.
The same problem may occur regardless of types of the images to be scanned in a flatbed scanner (an image scanning apparatus where a film is placed on a transparent original stage larger than the film).
This is because, in the flatbed scanner, a full transmission area where the film is not placed is scanned together with an area where the film is placed.
To be more specific, the full transmission area becomes a non-effective picture having a significantly high intensity compared to an effective picture.
Note that, users of the flatbed scanner visualize images obtained by the pre-scanning, and distinguish the non-effective picture such as the foregoing base, luminescent point, and full transmission area from the effective picture. The users can cover the non-effective picture with a prepared mask.
However, this is a complicated processing for the users. Besides, it is very difficult to cover minute luminescent points with the mask.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an image scanning apparatus capable of obtaining an image signal
Lee Patrick J.
Nikon Corporation
Oliff & Berridg,e PLC
Porta David
LandOfFree
Image scanning apparatus, control program of the same, and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image scanning apparatus, control program of the same, and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image scanning apparatus, control program of the same, and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3301058