JPH01211709A - Automatic focusing mechanism for photographic film reader - Google Patents

Abstract

PURPOSE:To enable focusing without being affected by a read image on a photographic film by controlling the focus adjusting mechanism by using a frequency component correlating to the granularity of the photographic film as the read image as focus information. CONSTITUTION:Focus control is carried out according to the granularity which is distributed irregularly over the entire surface of the photographic film. Namely, the high frequency component correlating to the granularity of the photographic film as the read image is utilized as the focus information (control signal). Consequently, the focusing is carried out without being affected by the read image on the photographic film. Even if there are a few developing particles or color element cloud at an unexposed part of the photographic film, the granularity is not 0, so the focusing is performed even by using the granularity of the unexposed part.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention provides an overlay mechanism suitable for use in a photographic film reader.

(Prior Art) Conventionally, in video cameras, image reading devices, etc., the level change of high frequency components in the captured (read) image signal is used as focus information, and the point at which the level of this high frequency component is maximum is used. An autofocus mechanism that focuses on the subject has been put into practical use.

(IJ/JXM) However, if the subject changes monotonically, such as a wall, and is even 4 f high, it is difficult to capture the image during focus! There is a level change in the high frequency component of the image signalg) L! However, it is difficult to detect the focus.

This is limited to cases where the subject is not a direct image such as a wall.6
This problem also occurs when reading a photographic film in which a monotonous object such as a wall 41 or a wall 41 is imaged.

Furthermore, when obtaining an image signal by conveying an image using a one-dimensional line transfer device, as in the case of a film-taking device, there is a case where a two-dimensional image conveying element is used, as in a general video camera. In comparison, during focusing, only a part of the image to be read is used, making focus detection more difficult and prone to noise.

(Means for Solving the Problems) In order to solve the above-mentioned problems (1), the present invention provides an image signal read from an image to be read by converting a level change of a high frequency component into focus information. The point where the level of the frequency component is maximum is set as the in-focus point in the focus mechanism O1 to d3, and the frequency component correlated with the graininess of the photographic film that is the image to be read is used as the focus information,
An autofocus mechanism for a photographic film reader configured to control a focus adjustment mechanism is provided.

(Function) Focus control is performed based on the graininess of the photographic film, which is irregularly distributed over the entire surface of the photographic film.

(Embodiment) An embodiment of the autofocus mechanism for a photographic film reader according to the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of the autofocus A-cass mechanism.

Light emitted from a light source 1 passes through a photographic film 2, which is an image to be read, and is imaged by a lens group 3 on a moving plane (a plane perpendicular to the paper plane) of an image sensor (line sensor). Images U,' of the photographic film 2 are sequentially taken by scanning in the main and sub-scanning directions. The read image signal is converted from an analog signal to a digital signal by an A/D converter and stored in the image memory 6.

The accumulated image signals are sequentially read out by the MPU 7 and transferred to the buffer memory 6' for the required processing. Based on the performance results, the MPU 7 sends a roll signal to the focus adjustment mechanism 8, and the lens group 5) moves back and forth in accordance with this control signal.
Focus adjustment is made.

The MPU 7 detects the level of the spatial (spatial) frequency component that correlates with the graininess of the photographic filter 2 in the read image signal and uses it as focus information, and determines the point where this level reaches its maximum as the in-focus point. I am sending out Con 1-Roll Shinyumi.

That is, the present invention is characterized in that a high frequency (spatial) frequency component correlated with the graininess of photographic film, which is an image to be read, is used as focus information (control signal).

Here, the graininess of photographic film will be explained. Graininess in photographic film refers to the collection of developed silver particles (in black and white films) or dye clouds (in color films) that appear because they are irregularly distributed. Graininess varies from film to film (itself), and also changes depending on exposure and visual image quality.

Quantitative measure of this graininess 3! I! What is expressed by m is the granularity. Granularity is measured using a microdensitometer with an aperture of constant diameter, and is defined as the standard deviation of minute area density. 110
If the page is J, generally an averture with a diameter of 48 μm is used, and this corresponds to the diameter of 48 μm (space).
It is believed that there is a strong correlation between frequency components and the graininess (granularity). .

By the way, as a method for detecting high frequency components of an image signal by digital processing, a method 11- based on a Laplacian filter (second-order differential) can be used.

L2 ZJJ-l 2'ir-(X'+'-++
x・+1) 1 (However, as shown in FIG. 2, xi is the pixel (image) data
If 1ill is the average of m pixels of I, and r is the number of pixels in the buffer memory, then there is a relationship of N=n/m. ) Generally, it is known that the index [- calculated by the above formula represents the level of a specific (spatial) frequency component that is applied to the image signal by the value of the above set value m.

Based on the above, the autofocus mechanism according to the present invention is constructed as follows. FIG. 3 is a configuration diagram specifically showing the optical system in FIG. 1.

As shown in the figure, for example, the image to be read (photographic film 2) is focused on the line lens 4 by the lens group 3 so as to be magnified approximately 2.7 times, and then the photographic film 2 is focused on the image d3. The upper 4 (1 m (of aperture A) covers approximately 128 μm of i3L with line lens 4 soil. Therefore,
For example, the size of one pixel of line lens 4 is approximately 62.
5 μm, set m = 2 in the above index formula, and calculate the sum of the absolute values of the second-order differentials V using 1L, which is the average value of every 2 pixels of the line sensor 1 and 4. ,~
, index (- represents the level of the frequency component correlated with the graininess of the photographic film L2, which is the image to be read.

Here, M p U 7 calculates the fingers 4g, 1- from the image data in the buffer 1 memory 6' using the iZ1 index formula (m=2).
In order to move the lens group 3 so that the index 1- becomes the maximum value, a control roll signal is sent to the focus adjustment mechanism 8 to obtain focus.

In this way, since the focus information uses the spatial frequency component that correlates with the graininess that is irregularly distributed over the entire surface of the photographic film 2, it is difficult to read the photographic film 2. It depends on whether it is influenced by the image or whether it is in focus.

Incidentally, even if there are a few developed silver particles or dye clouds in the unexposed areas of the photographic film, the granularity is not zero. Therefore, focusing can also be achieved by utilizing the graininess of the unexposed portion.

(Effects of the Invention) The autofocus device for a photographic film reading device according to the present invention (14 uses a level change of a high frequency component in a read image signal as focus information, and the point at which the level of this high frequency component becomes maximum) In an autofocus mechanism that uses 7-8' true film as a focusing point, the frequency component correlated with the graininess of the 7-8' true film, which is the image to be read, is used as the above-mentioned A-dust information. Based on the graininess (quality) of photographic film that is irregularly distributed in It depends on what you take.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of an autofocus mechanism for a photographic film reader according to the present invention, and Fig. 2 shows a configuration of the pixels (1-ta) of the buffer memory and the parameters used for the index line. FIG. 3, a diagram showing the relationship, is a configuration diagram specifically showing the optical system in FIG. 1. 2... Photographic film, 4... Rhinelenbo, 6'.
... Buffer 7 memory, 7... MPU, 8... Focus adjustment mechanism. -8= 00-1

Claims (1)

[Claims] In an autofocus mechanism, the change in the level of high frequency components in the image signal read from the image to be read is used as focus information, and the point where the level of this high frequency component is maximum is the focal point. An autofocus mechanism for a photographic film reading device, characterized in that the focus adjustment mechanism is controlled using a frequency component correlated with the graininess of the film as the focus information.