CN1259794C - Method of reading image signal from image senser - Google Patents
Method of reading image signal from image senser Download PDFInfo
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- CN1259794C CN1259794C CNB2004100087887A CN200410008788A CN1259794C CN 1259794 C CN1259794 C CN 1259794C CN B2004100087887 A CNB2004100087887 A CN B2004100087887A CN 200410008788 A CN200410008788 A CN 200410008788A CN 1259794 C CN1259794 C CN 1259794C
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Abstract
The present invention relates to a method of reading image signals in an image sensor, which belongs to the technical field of a complementary metal oxide semiconductor image sensor. The method firstly selects scanning lines in the images in turn; the selected scanning lines are scanned by the scanning frequency of columns; the pixels of each column are scanned; the low-pass filtering of each column of pixel signals with the cut-off frequency of Wn is carried out; the analogue-digital conversion of the signals is carried out after the low-pass filtering, and the digital image signals are obtained. The cut-off frequency Wn of the method of the present invention is greatly lower than the column scanning frequency, and the frequency of the analogue-digital conversion is also greatly lower than the column scanning frequency. Accordingly, when a circuit is realized, high-speed image acquisition can be completed with low-speed analogue-digital conversion. The circuit realized by the method of the present invention only uses an analogue-digital converter, the sampling frequency of which is greatly lower than the column scanning frequency, and accordingly, the area and the power consumption performance of the circuit are more favorable than that of the image sensor of the analogue-digital converter, and since the speed rate of the analogue-digital conversion is low, the generated data quantity is small, and the image processing of the rear end is convenient.
Description
Technical field
The present invention is a kind of reading method and circuit thereof of imageing sensor picture signal, belongs to complementary metal oxide semiconductors (CMOS) (hereinafter to be referred as CMOS) image sensor technologies field.
Background technology
Cmos image sensor is to scan to read out by the monochrome information to each pixel to obtain complete image.Picture signal is to utilize by to the scanning of pixel procession in existing cmos image sensor, then the picture element signal of sweep gate is carried out analog-to-digital method and obtains picture signal.Along with the raising of the resolution and the image acquisition speed of cmos image sensor, adopt traditional reading method to need very high-frequency analog-to-digital conversion, need the very high analog to digital converter of sample frequency when promptly circuit is realized.In order to reduce the analog-to-digital conversion frequency, there are many methods simultaneously a plurality of pixels to be carried out analog-to-digital conversion by using the multichannel analog-to-digital conversion.Adopt the method for multimode number conversion when circuit is realized, to need a lot of analog to digital converters, so not only increased the power consumption and the area of circuit, and increased cost.Simultaneously, must reduce the light-receiving area of each pixel, the sensitivity of cmos image sensor is reduced greatly because other area of circuit increases, the image of influence obtain quality.The requirement that the modern CMOS of shortcoming incompatibility of obvious this method is extensive and very lagre scale integrated circuit (VLSIC) develops to the high-speed low-power-consumption direction is especially for various mobile electronic equipments, such as face-to-face communication mobile phone, various video cameras etc.
Summary of the invention
The objective of the invention is at existing cmos image sensor under the situation of high-resolution and hi-vision acquisition speed, need a lot of roads analog-to-digital conversion to carry out the various drawbacks of being brought simultaneously, propose the reading method of picture signal in a kind of imageing sensor, obtain so that when circuit is realized, can finish rapid image with the analog-to-digital conversion of low speed.
The reading method of picture signal in the imageing sensor that the present invention proposes comprises following each step:
(1) from image, selectes scan line successively, selected scan line is pressed each row pixel of column scan frequency scanning successively;
(2) above-mentioned each row pixel signal is carried out the low-pass filtering that cut-off frequency is Wn;
(3) signal after the low-pass filtering is carried out analog-to-digital conversion, obtain data image signal.
The reading method of picture signal at first carries out the low-pass filtering that cut-off frequency is Wn to every capable image pixel signal in a kind of imageing sensor that the present invention proposes, then with the sampling clock frequency be the analog-to-digital conversion of 2Wn to filtering after picture element signal sample.Because in every row or every column signal of image, the radio-frequency component of signal seldom, so cut-off frequency Wn can be well below the column scan frequency.Because Wn is well below the column scan frequency, so analog-to-digital frequency also well below the column scan frequency, is obtained thereby can finish rapid image with the analog-to-digital conversion of a low speed when circuit is realized.This method not only can only be used one tunnel analog-to-digital conversion to finish rapid image and obtain, and analog-to-digital frequency is well below the frequency of column scan.Because the circuit that adopts method of the present invention to realize has only used the analog to digital converter of a sample frequency well below the column scan frequency, so the area of circuit and power consumption performance are all better than the cmos image sensor of existing multimode number converter; Because analog-to-digital speed is low,, brought convenience for the image processing of rear end again so the data volume that produces is little.
Description of drawings
Fig. 1 to Fig. 6 is the explanation to effect of the present invention.
Embodiment
The reading method of picture signal in the imageing sensor that the present invention proposes, selected scan line from image is pressed each row pixel of column scan frequency scanning successively to selected scan line at first successively; Each row pixel signal is carried out the low-pass filtering that cut-off frequency is Wn; Signal after the low-pass filtering is carried out analog-to-digital conversion, obtain data image signal.
In above-mentioned reading method, in order to simplify the image Compression process of back, requirement is very high for the acquisition speed of image, so the amount of images of obtaining in the per second is very big, like this for the very high row and column sweep speed of high resolution CMOS image sensor inevitable requirement, wherein column scan speed be line scan speed horizontal resolution doubly.If for resolution is that 1000 * 1000 cmos image sensor per second obtains 1000 pictures, then needing line-scanning frequency is 1MHz, and the column scan frequency is then up to 1000MHz.High like this sweep speed is very important in practice, realizes and the analog to digital converter of 1000MHz is very difficult, so must adopt a plurality of analog to digital converters simultaneously a plurality of pixels to be carried out analog-to-digital conversion.The present invention is in order to lower the operating rate of analog to digital converter under the condition that satisfies the image quality requirement, to the analysis of having carried out frequency spectrum of the every capable signal of image, discovery is very very little in the shared ratio of every capable signal medium-high frequency composition, can be at first to its low-pass filtering and then use greater than the sample rate of 2 times of filter cutoff frequencies filtered signal is sampled, so also can recover satisfied image.Here the cut-off frequency of filter can be optimized according to the practical application needs.
Introduce operation principle of the inventive method and the relation between low-pass filtering cut-off frequency and the column scan signal frequency below in conjunction with accompanying drawing, with MATLAB the original image of a JPG form has been carried out low-pass filtering, the cut-off frequency Wn of filter is respectively 1/50,1/25,1/12.5,1/10 and 1/8 with the ratio of column scan signal frequency Fs.Figure (1) is the picture of original JPG form, figure (2) is the result of Wn/Fs=1/50, and figure (3) is the result of Wn/Fs=1/25, and figure (4) is the result of Wn/Fs=1/12.5, figure (5) is the result of Wn/Fs=1/10, and figure (6) is the result of Wn/Fs=1/8.Observe as can be seen by picture that these were handled, when Wn/Fs 〉=1/10, the image after the low-pass filtering and the difference of original image are very little, with the naked eye are difficult to its difference of differentiation; And when Wn/Fs≤1/25, with the naked eye just be easy to aware the degradation of image.Can choose different cut-off frequencies according to different application.
Claims (1)
1, the reading method of picture signal in a kind of imageing sensor is characterized in that this method may further comprise the steps:
(1) from image, selectes scan line successively, selected scan line is pressed each row pixel of column scan frequency scanning successively;
(2) above-mentioned each row pixel signal is carried out the low-pass filtering that cut-off frequency is Wn, cut-off frequency wherein is lower than described column scan frequency;
(3) signal after the low-pass filtering is carried out analog-to-digital conversion, analog-to-digital sampling clock frequency is 2Wn, obtains data image signal.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNB2004100087887A CN1259794C (en) | 2004-03-19 | 2004-03-19 | Method of reading image signal from image senser |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CNB2004100087887A CN1259794C (en) | 2004-03-19 | 2004-03-19 | Method of reading image signal from image senser |
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| CN1564579A CN1564579A (en) | 2005-01-12 |
| CN1259794C true CN1259794C (en) | 2006-06-14 |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| EP1966739B1 (en) * | 2005-12-21 | 2012-06-06 | Koninklijke Philips Electronics N.V. | Biometric information detection using sweep-type imager |
| CN104658488B (en) * | 2013-11-18 | 2017-09-29 | 华为技术有限公司 | Downsapling method and device |
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