JPS62299948A - Automatic setting method for illumination light quantity - Google Patents

Abstract

PURPOSE:To automatically adjust the light quantity of an illuminating device so that the distribution of a luminance histogram is a proper state by inputting an image with high contrast following the change of an objective image. CONSTITUTION:An object illuminated by the illuminating device 1b is image- picked up by a camera 15 and a luminance histogram indicating the number of picture elements for luminance is formed from the image data. A difference l1 (=a-L) between the minimum level L of the image luminance and a minimum luminance level (a) including the picture element and a difference l2 (=H-b) between the maximum level H of the image luminance and the maximum luminance level (b) including the picture element are found out respectively and the light quantity of the illuminating device 1b is automatically adjusted so that the difference between l1 and l2 is reduced. The luminance histogram can be moved to the center of the L and H and optimum illuminating light quantity can be obtained by controlling the illuminating light so that the difference between l1 and l2 is reduced, preferably l1=l2 is formed.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Summary] When an object illuminated by an illumination device is imaged with a camera, in order to input an image with good contrast that follows changes in the object image, To automatically adjust the amount of light of a lighting device so that the distribution of a brightness histogram is in an appropriate state.

[Industrial application field]

The present invention relates to a method for automatically setting the amount of illumination light for an object when the object is imaged with a camera.

[Conventional technology]

When an object is imaged with a television (TV) camera and the image information is used to detect the position of a pattern on a printed circuit board, an important point is how to input an image with good contrast. When an object is illuminated by a lighting device, one condition for inputting an image with good contrast is to set the amount of illumination light to an optimum value depending on the object. Conventionally, it has been common practice to manually adjust the amount of illumination light based on experience or intuition, depending on the brightness of the object.

[Problem that the invention seeks to solve]

For example, when detecting the position of a pattern on a printed circuit board, the illumination device often illuminates the printed circuit board from the opposite side of the TV camera (back lighting). In some cases, the intermediate layer pattern blocks the illumination light that passes through the substrate, resulting in an insufficient amount of illumination light to the target. Conversely, when there is no intermediate layer pattern in the vicinity of the surface layer pattern, the amount of illumination light on the object may become excessive. The purpose of the present invention is to manually produce images with good contrast and contrast by automatically adjusting the amount of illumination light to the optimum value when the object to be imaged or the conditions change.

[Means for solving problems]

According to the present invention, an object illuminated by an illumination device is imaged by a camera, a brightness histogram representing the number of pixels with respect to brightness is created from the image data, and the lowest level (L) of image brightness and the lowest level where pixels exist are created. Find the difference 1r<-a L) from the brightness level (a), and find the difference #2 (-H-b) between the highest level of image brightness (H) and the highest brightness level where the pixel exists (b). , 11 and 12 is automatically adjusted to automatically adjust the light amount of the illumination device so that the difference between , 11 and 12 is reduced.

[For production]

The brightness histogram is biased toward the lowest level (L) when the amount of illumination light is insufficient, and conversely toward the highest level (H) when the amount of illumination light is excessive.

Therefore, as mentioned above, preferably 12. By adjusting the amount of illumination light so that =12, the brightness histogram can be moved to the center between L and H, making it possible to obtain the optimum amount of illumination light.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows an apparatus for adjusting the amount of illumination light when the surface pattern of a printed circuit board is imaged with a T'V camera and the pattern position is detected. The printed circuit board 10 is a multilayer printed circuit board, and has several intermediate layer patterns 12, 13 inside a board body 11 made of a light-transmitting material, and a surface pattern 14, which is the object of position detection, on the surface. Printed circuit board 10
There is a TV camera 15 above the surface pattern 14 side, which images the surface of the printed circuit board 10 on which the target pattern 14 is located. On the other hand, below the printed circuit board 10 is a lighting device 1.
6, and the printed circuit board 10 is used as bank lighting from the back side.
illuminate. The image signal captured by the TV camera 15 is input to the frame memory 17 of the computer, converted into a digital image, and then input to the processing device 18. The processing device 17 determines the optimum amount of illumination light, ie, the voltage (V) of the illumination device 16, from the input image signal as will be described later, and performs feedbank control of the illumination device 6.

FIG. 2 is an image on the frame memory 17, in which the target (surface) pattern I4 is clearly photographed with good contrast, and the intermediate layer patterns 12 and 13 are photographed vaguely.

Next, a procedure for automatically setting the amount of illumination light, that is, the voltage (V) of the lighting device 16 will be described. First, illumination light is irradiated from the back surface of the printed circuit board 10 using an average voltage (V) of the illumination device 16 determined in advance through experiments. Next, an image from the TV camera 15 (FIG. 2) is taken into the frame memory 17 in response to a start signal from the processing device 18. Next, the image data in the frame memory 17 is read out and a brightness histogram as shown in FIG. 3 is created. This brightness histogram is expressed by the number of pixels (total number of pixels is, for example, 256 x 256) or frequency with respect to the brightness level (for example, 256 levels). L is the lowest level of image brightness, and H is the highest level of image brightness.

Therefore, the lowest level (a) where a pixel exists is found from the L level of image brightness, and the difference 6+(-a-L) is found. Similarly, find the highest level (b) where a pixel exists from the H level of image brightness, and calculate the difference 1 z (=
Find Hb). Next, the lighting device 16 of J and Il2
The standard voltage is set by preliminary experiments. )
Next, apply the corrected voltage (vn) to the illumination device 1 as shown below.
6, input the start signal again, capture the target image, and proceed to the next process.

In FIG. 4, there are intermediate layer patterns 12 and 13 within the imaging range of the printed circuit board 10, and the amount of light from the back illumination from the illumination device 16 is blocked by the intermediate layer patterns 12 and 13, illuminating the target (surface) pattern 14. This is a case where the amount of light for the image is insufficient and the target (surface) pattern 14 is photographed darkly (Fig. 4 (a)). In this case, the brightness histogram is biased towards the lowest level (L) (Fig. Figure (b)).

On the other hand, in FIG. 5, there is no intermediate layer pattern within the imaging range of the printed circuit board 10, and the target (surface pattern) 14 is an isolated pattern, and the amount of transmitted light due to back illumination from the illumination device 16 is large, resulting in an excessive amount of illumination light. (
In this case, the brightness histogram is biased toward the highest level (H) (FIG. 5(b)). FIG. 6 shows a brightness histogram when the amount of illumination light is corrected as described above, and in both cases, the brightness curve after correction moves to the center regarding the lowest level (L) and the highest level (H), Provides the optimum amount of illumination light.

〔Effect of the invention〕

According to the present invention, even when the situation of the object changes, the amount of light illuminating the object can be automatically adjusted to the optimum value, and therefore it is possible to compensate for contrast deterioration due to insufficient or excessive amount of illumination light.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a device implementing the automatic setting method of illumination light intensity of the present invention, Fig. 2 is a diagram showing an image on a frame memory, Fig. 3 is a luminance histogram of image data, and Fig. 4 (a
), (b) are images and brightness histograms when illumination light is insufficient, Figures 5 (a) and (b) are images and brightness histograms when illumination is excessive, and Figure 6 is correction of illumination light. This is the subsequent brightness histogram. 10... Printed circuit board, 12.13... Intermediate layer pattern, 14... Target (surface) pattern, 16... Illumination device.

Claims (1)

[Claims] 1. Image the object illuminated by the illumination device with a camera,
A brightness histogram representing the number of pixels with respect to brightness is created from the image data, and the difference l_1 (
=a-L) and the difference l_2(=
H-b), and automatically adjusts the light amount of the lighting device so that the difference between l_1 and l_2 becomes small.