CN100594418C - Image capturing device, focusing method thereof and method for determining image contrast value - Google Patents

Abstract

An image capturing device, a focusing method thereof and a method for determining an image contrast value are provided. Firstly, performing auto-focusing according to a contrast value of an image generated by a lens on a photosensitive component, wherein the determination of the contrast value of the image comprises: selecting an area of the image; determining the absolute value of the difference in brightness for each set of neighboring pixels over the area; and determining a specific brightness difference absolute value as the contrast value of the image according to the distribution of the obtained brightness difference absolute values, wherein the distribution is obtained by the corresponding relation of the brightness difference absolute value and the brightness difference absolute value of the same color and the number of strokes of adjacent pixels.

Description

Image capture device, its focusing method and method for determining image contrast value

technical field

The present invention relates to image processing technology, and particularly relates to an image capturing device, its focusing method and a method for determining image contrast value.

Background technique

The autofocus function of the camera can measure the position of the object relative to the lens with the help of a distance measuring device, and adjust the lens distance to focus accordingly. Passive auto-focus digital cameras do not require a distance measuring device, but use the digitized image captured by the lens, and use the value after frequency domain conversion as the key value of sharpness, so as to change the focal length of the lens or the object distance to find the key value The maximum value for the clearest picture.

The focus search method is the current development topic of passive auto focus. Today's research and development of digital cameras all use a dedicated digital signal processor (Digital Signal Processor, referred to as DSP), and there is hardware in the DSP to detect whether the focus is successfully completed. However, this focusing method still has disadvantages. For example, when the focus object is a hair, the DSP generally determines the brightness values of the pixels (Pixel) in the picture by subtracting them and then taking the average value or summing them up as a contrast value, but this will make the surrounding hair The contrast value obtained by subtracting the pixel brightness is averaged, so that the proportion of the pixel brightness difference in the contrast value is reduced, and accurate focusing cannot be achieved.

Contents of the invention

In view of this, the object of the present invention is to provide an image capture device, a focusing method thereof, and a method for determining an image contrast value.

Based on the above purpose, the present invention provides an image capture device, comprising: a photosensitive component, used to convert light beams into electronic signals; a lens, used to form an image on the above photosensitive component; a processor, based on the above photosensitive component The contrast value of an image generated on the above-mentioned image is used to perform auto-focus, wherein the above-mentioned processor selects an area of the above-mentioned image, determines the absolute value of the brightness difference of each group of two adjacent pixels with the same color on the above-mentioned area, and obtains according to the above-mentioned determination The distribution of adjacent pixels of the same color with the same absolute value of brightness difference determines a specific absolute value of brightness difference as the contrast value of the above-mentioned image. The corresponding relationship of numbers is obtained.

In the image capture device according to the present invention, wherein the number of entries with the same value in all the absolute values of the brightness difference obtained by the processor is counted, wherein the distribution includes the number of entries with the same absolute value of the brightness difference corresponding to the absolute value of the brightness difference, The above-mentioned processor starts to accumulate the number of pens with the same absolute value of the above-mentioned brightness differences from the maximum value to the minimum value of the absolute value of all the brightness differences above, and when the accumulated total number of pens is added to the number of pens of the first absolute value of the brightness difference, it is equal to or If it is greater than a predetermined number, the contrast value of the image is the first absolute value of brightness difference, wherein both the accumulated total number and the first absolute value of brightness difference refer to the same absolute value of brightness difference.

In the image capture device of the present invention, obtaining the number of items with the same absolute value of brightness difference further includes: after the processor determines the absolute value of brightness difference of two adjacent pixels with the same color in the above region, That is, the absolute value of the brightness difference is immediately classified; and after the above-mentioned processor determines the absolute value of the brightness difference of each group of two adjacent pixels with the same color on the above-mentioned area, the pen with the same absolute value of the above-mentioned brightness difference can be obtained at the same time. number.

According to the image capture device of the present invention, its focusing method includes: performing auto-focusing according to the contrast value of an image generated by a lens on a photosensitive element; the optimal contrast value of the image; and when searching for the optimal contrast value of the above image fails, automatically search for the optimal contrast value of the above image by using a focusing method using part of the image.

In the focusing method of the present invention, the above-mentioned focusing method using the whole image and the above-mentioned focusing method using part of the image respectively select different regions of the above-mentioned image to determine the contrast value of the above-mentioned image.

In the focusing method of the present invention, in the focusing method using partial images, a specific absolute value of brightness difference is determined as the contrast value of the image from the distribution of absolute brightness difference values of adjacent pixels in a region of the image.

In the focusing method of the present invention, wherein, the image range selected by the focusing method using the entire image is A, and the image range selected by the focusing method using part of the image is B, and the range B of the above-mentioned area is not equal to the range of the above-mentioned image Range A.

According to the present invention, the method for determining the image contrast value includes: generating an image on a photosensitive component according to a lens, wherein the range of the above image is A; selecting an area of the above image, wherein the range of the above area is B; determining the above The absolute value of the brightness difference of each group of adjacent pixels on the area; and determine a specific absolute value of the brightness difference as the contrast value of the above-mentioned image according to the distribution of the absolute value of the brightness difference obtained from the above determination, the distribution is determined by the absolute value of the brightness difference and the brightness difference The corresponding relationship of the number of adjacent pixels of the same color with the same absolute value difference is obtained.

In the method for determining the contrast value of an image according to the present invention, the range B of the above-mentioned region is not larger than the range A of the above-mentioned image.

The method for determining the contrast value of an image according to the present invention further includes: statistically determining the number of strokes with the same value in all the absolute values of the above-mentioned brightness differences obtained, so as to obtain the above-mentioned distribution, wherein the above-mentioned distribution includes the absolute value of the brightness difference corresponding to the absolute value of the brightness difference The same number of pens; from the maximum value to the minimum value of the absolute value of all brightness differences above, start to accumulate the number of pens with the same absolute value of brightness difference; and when the accumulated total number of pens is added to the number of pens of the first absolute value of brightness difference or greater than a predetermined number, the contrast value of the above-mentioned image is the first absolute value of brightness difference, wherein the total accumulated number and the first absolute value of brightness difference both refer to the same absolute value of brightness difference.

The method for determining the image contrast value according to the present invention, wherein obtaining the number of strokes with the same absolute value of the brightness difference further includes: after each determination of the absolute value of the brightness difference of a group of adjacent pixels on the above-mentioned area, immediately absolute the brightness difference Values are classified; and after the absolute value of the brightness difference of each group of adjacent pixels on the above-mentioned area is determined, the number of strokes with the same absolute value of the above-mentioned brightness difference can be obtained at the same time.

In order to make the above-mentioned objects, features and advantages of the present invention more comprehensible, the detailed embodiments are described in detail below together with the accompanying drawings.

Description of drawings

Fig. 1: shows the structural block diagram of an embodiment of an image capture device;

Figure 2: A flowchart showing an embodiment of a focusing method;

Figure 3: A flowchart showing an embodiment of a focusing method;

Figure 4: Displaying a passive focus image;

Figure 5: a flow chart showing an embodiment of a second focusing method;

Figure 6: Displays the pixel distribution of one of the image regions of the image in Figure 4;

Figure 7: Decision flow chart showing contrast values; and

Figure 8: Displays the distribution of the number of pens whose absolute value of brightness difference corresponds to the same absolute value of brightness difference.

Detailed ways

A method for determining a contrast value, an image capture device using the method, and a focusing method are disclosed below. It should be understood that the configurations of the following entities and steps are just examples and can be adjusted.

In the image capture device 100 in FIG. 1 , the processor 1 is coupled to the memory 2 , the photosensitive element 4 , the input device 6 , the lens 8 and the control unit 9 . The processor 1 is a digital signal processor (Digital Signal Processor, DSP for short). The control unit 9 can be integrated in the processor 1 .

The photosensitive element 4 can be composed of complementary metal-oxide semiconductor (Complementary Metal-Oxide Semiconductor, CMOS for short) or charge-coupled device (Charge-Coupled Device, CCD for short). The photosensitive element 4 receives the light beam from the lens 8, so as to convert it into an electronic signal as image data.

The control unit 9 is coupled to the focusing device 91 , and drives the focusing device 91 according to the image information provided by the processor 1 , so as to automatically adjust the position of the lens 8 or the photosensitive element 4 to achieve the purpose of focusing. The control unit 9 activates autofocus depending on the state of the input device 6 . The input device 6 may include a shutter release button on the image capture system 100 or an external activation control device.

The lens 8 can be implemented by various lenses. The light beam passes through the lens 8 to form an image on the photosensitive component 4 . For example, the lens 8 may consist of several lenses, and the focusing device 91 may include mechanical components for driving the position of the focusing lens 81 .

Referring to FIG. 2 , the processor 1 moves the position of the focusing lens 81 , and performs auto-focus according to the contrast value of the image produced by the lens 8 on the photosensitive component 4 . Processor 1 can focus in different ways.

During the auto-focusing process, the processor 1 uses the first method to focus to search for the best contrast value of the image (step S2 ), and judges whether the best contrast value is successfully found (step S4 ). When the optimal contrast value is successfully found, the processor 1 ends the focusing operation. When searching for the best contrast value of the image fails, the processor 1 automatically searches for the best contrast value of the above-mentioned image by a second method (step S6 ), wherein the second method is not equal to the first method.

The first method and the second method can respectively take different regions of the image to determine the contrast value of the image. For example, the first method uses the entire image for determination; the second method takes the middle 1/25 rectangular area of the entire image to determine the contrast value of the image, wherein the length and width of the rectangular area selected by the second method are respectively the entire 1/5 times the length and width of the image. It should be understood that, in practice, the regions selected by the second method can be of different shapes and sizes, and can also be in different positions of the above-mentioned image.

Referring to FIG. 3, the processor 1 moves the focus lens 81 within the movable range of the focus lens 81 (step S10). When the focusing lens 81 is in each position, a corresponding image will be formed on the photosensitive element 4 (step S12 ). The processor 1 determines the contrast value of each corresponding image (step S14), finds the image with the best contrast value (step S16), and moves the focusing lens 81 to the corresponding position of the image (step S18). In this way, the processor 1 performs auto-focus according to the contrast value of the image generated on the photosensitive element 4 . This focusing method can preferably utilize the technology disclosed in the description of the Taiwan patent application titled "Automatic focusing method and image capture device using the above method". The focus lens 81 is moved with a larger precision unit to obtain a better contrast value and its corresponding position. The position corresponding to the absolute best contrast value is obtained by using the better contrast value and its corresponding position, and the other two data (there are two positions and their two contrast values before and after the corresponding position) by means of internal difference. And move the focusing lens 81 to this position.

FIG. 4 shows an image 200 displayed on the photosensitive element 4 when the focusing lens 81 is at a specific position (step S12 ). The image area 201 is a rectangular area of the middle 1/25 of the image 200 . In the above-mentioned second method, the processor 1 can take the image area 201 from the image 200, and then determine a specific absolute value of the brightness difference from the distribution of the absolute value of the brightness difference of adjacent pixels in the image area 201 as the contrast value of the image, Details are as follows.

Referring to FIG. 5, the processor 1 obtains the image area 201 of the image 200 (step S20), determines the absolute value of the brightness difference of each group of adjacent pixels on the image area 201, and records the accumulated number (step S22). The processor 1 obtains the distribution of the absolute value of the brightness difference in the image area 201 through determination (step S24 ). And according to the distribution, a specific absolute value of brightness difference is determined as the contrast value of the image 200 (step S26).

The method for obtaining the distribution of the absolute value of the brightness difference is illustrated below with an example. The image 200 can conform to a Bayer pattern, and the distribution of the absolute value of its brightness difference can be determined by determining the absolute value of the brightness difference of each group of two adjacent pixels with the same color in the image area 201, and using the processor 1 to classify and calculate the statistics. have to. As shown in FIG. 6 , the pixels v1 , v3 and v5 are all red pixels, and the pixels v2 and v4 are all green pixels. Processor 1 determines the absolute value of brightness difference between pixels v1 and v3, and classifies according to this value; determines the absolute value of brightness difference between pixels v2 and v4, and classifies according to this value; determines the absolute value of brightness difference between pixels v3 and v5, And classify by this value...etc. In this way, after determining the absolute value of the brightness difference of each group of two adjacent pixels with the same color in the image area 201 , the distribution of the absolute value of the brightness difference can be obtained simultaneously.

To further illustrate, the processor 1 subtracts the luminance values of adjacent pixels of the same color in the image area 201 to obtain an absolute value, and then records the absolute value of the luminance difference into an array pixelsAF[]. The initial value of the elements pixelsAF[0] to pixelsAF[255] in the array pixelsAF[] is set to 0; and the Abs(x, y) function is used to represent the absolute value of the brightness difference between two adjacent pixels x and y of the same color. Referring to FIG. 7 , processor 1 obtains a group of two adjacent pixels x and y of the same color (step S30 ); determines the absolute value of brightness difference Abs(x, y) of pixels x and y (step S32 ). If the value of Abs(x, y) is K (K is a positive integer), processor 1 adds 1 to the value of pixelsAF[K] (step S34). For example, in the image area 201, if there is a group of two adjacent pixels with the same color and the absolute value of the brightness difference Abs(v1, v3) is 255, add 1 to the value of the element pixelsAF[255]; When the absolute value of the brightness difference Abs(v2, v4) of adjacent and same-color pixels v2 and v4 is 230, add 1 to the value of the element pixelsAF[230].

The processor 1 determines whether the pixels x and y are the last two adjacent pixels of the same color in the image area 201 (step S36 ). If not, another group of two adjacent pixels with the same color in the image area 201 is obtained again (return to step S30); if yes, the next step S38 is executed. After the above determination is completed, the number of items with the same absolute value Abs(x, y) can be known immediately. For example, if there are 2 items with the absolute value of pixel brightness difference Abs(x, y)=255, record pixelsAF[255]=2 , if there are 4 items with the absolute value of the pixel brightness difference Abs(x, y)=254, then record pixelsAF[254]=4, so that the statistical chart as shown in Figure 8 can be obtained, that is, the absolute value of the brightness difference and the absolute value of the brightness difference The number of pens with the same value is distributed as 300.

Finally, according to the result shown in FIG. 8 , the processor 1 accumulates the number of strokes whose absolute value of the brightness difference is the same from the maximum value to the minimum value. Initially, the processor 1 first presets the total number of initialized sums to be 0, and when the accumulated total number of sums is equal to or greater than a predetermined number P after adding a sum with the same absolute value of the brightness difference, the processor 1 immediately sets the image 200 The contrast value of is the absolute value of the brightness difference. Know from experiment, predetermined number P is set as 10 better, so here predetermined number P=10, and preset variable i=255 (step S38); Then carry out accumulation, Sum=Sum+pixelsAF[i] (step S40 ); Processor 1 determines whether Sum≥P (step S42). If no, processor 1 subtracts 1 from the value of variable i (step S44), and then continues to accumulate (return to step S40); if so, processor 1 then sets the contrast value of image 200 as the value of variable i (step S46 ). For example, if the value of the variable i is 253 at this time, the processor 1 sets the contrast value of the image 200 to 253.

By using the above method, the comparison value of several different positions can be counted to find the maximum value, and finally the focus lens 81 is driven to the position corresponding to the maximum value to complete the focusing.

The above method determines the contrast value based on the area of the image, where the contrast value is not obtained by averaging, but by determining the absolute value of the actual brightness difference between two adjacent pixels of the same color, and counting the distribution of the absolute value of brightness difference in this area. have to.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Do not depart from the patent scope of the present invention.

Claims (10)

1. An image capture device, characterized in that the image capture device comprises: A photosensitive element for converting light beams into electronic signals; A lens for forming images on the above-mentioned photosensitive components; a processor, performing autofocus according to the contrast value of an image generated on the photosensitive element, wherein the processor selects an area of the image, and determines the brightness of each group of two adjacent pixels of the same color on the area The absolute value of the difference, and according to the distribution of adjacent pixels of the same color with the same absolute value of the brightness difference determined above, a specific absolute value of the brightness difference is determined as the contrast value of the above-mentioned image. The distribution is determined by the absolute value of the brightness difference and the absolute value of the brightness difference The corresponding relationship between the numbers of the same color and adjacent pixels is obtained. 2. The image capture device as claimed in claim 1, wherein the number of items with the same value in all the absolute values of the brightness difference obtained by the processor is counted, wherein the distribution includes the absolute value of the brightness difference corresponding to the absolute value of the brightness difference For the number of strokes with the same value, the above-mentioned processor starts to accumulate the number of strokes with the same absolute value of the above-mentioned brightness difference from the maximum value to the minimum value of the absolute value of the above-mentioned all brightness differences, and when the accumulated total number of strokes adds a first absolute value of the brightness difference After the number of strokes is equal to or greater than a predetermined number, the contrast value of the above-mentioned image is the first absolute value of brightness difference, wherein the total number of accumulated strokes and the first absolute value of brightness difference both refer to the same absolute value of brightness difference. 3. The image capture device as claimed in claim 2, wherein obtaining the number of strokes with the same absolute value of the brightness difference further comprises: After the above-mentioned processor determines the absolute value of the brightness difference of a group of two adjacent pixels with the same color on the above-mentioned area, it immediately classifies the absolute value of the brightness difference; and After the processor determines the absolute value of the brightness difference between each group of two adjacent pixels with the same color and the same color in the above region, the number of strokes with the same absolute value of the brightness difference can be simultaneously obtained. 4. A focusing method for the image capture device according to claim 1, wherein the focusing method comprises: performing autofocus according to the contrast value of an image produced by a lens on a photosensitive element; during the autofocus process, searching for a contrast value of the image using a focusing method that utilizes the entire image; and When searching for the contrast value of the above-mentioned image fails, automatically search for the contrast value of the above-mentioned image by using a focusing method using a part of the image. 5. The focusing method according to claim 4, wherein the focusing method using partial images determines a specific brightness from the absolute value distribution of brightness differences between two adjacent pixels of the same color in a region of the image The absolute value of the difference was used as the contrast value of the above image. 6. The focusing method according to claim 5, wherein the image range selected by the focusing method using the entire image is A, the image range selected by the focusing method using part of the image is B, and the range B of the above-mentioned area is Not equivalent to range A of the image above. 7. A method for determining an image contrast value, characterized in that the method comprises: An image produced on a photosensitive element according to a lens, wherein the above-mentioned image range is A; Select an area of the above-mentioned image, wherein the range of the above-mentioned area is B; Determining the absolute value of the brightness difference of each group of two adjacent pixels with the same color on the above-mentioned area; and According to the distribution of adjacent pixels of the same color with the same absolute value of brightness difference determined above, a specific absolute value of brightness difference is determined as the contrast value of the above-mentioned image. The corresponding relationship of the number of adjacent pixels is obtained. 8. The method for determining the image contrast value according to claim 7, wherein the range B of the region is not larger than the range A of the image. 9. The method for determining image contrast value as claimed in claim 7, wherein the method for determining image contrast value further comprises: Statistically determine the number of pens with the same value in all the absolute values of the above-mentioned brightness differences obtained, so as to obtain the above-mentioned distribution, wherein the above-mentioned distribution includes the number of pens whose absolute values of the brightness differences correspond to the same absolute values of the brightness differences; From the maximum value to the minimum value of the absolute value of all the brightness differences above, start to accumulate the number of pens with the same absolute value of the brightness difference; and When the accumulated total number of strokes is equal to or greater than a predetermined number after adding the number of strokes of a first absolute value of brightness difference, the contrast value of the above-mentioned image is the first absolute value of brightness difference; Wherein the total number of accumulated strokes and the first absolute value of the brightness difference both refer to the same absolute value of the brightness difference. 10. The method for determining image contrast values as claimed in claim 9, wherein obtaining the number of strokes with the same absolute value of the above-mentioned brightness difference also includes: Classify the absolute value of the brightness difference immediately after determining the absolute value of the brightness difference between two groups of adjacent pixels with the same color in the above-mentioned area; and After determining the absolute value of the brightness difference of each group of two adjacent pixels with the same color and the same color in the above region, the above number of strokes with the same absolute value of the brightness difference can be obtained at the same time.

Images