CN100361019C - Method for implementing automatic exposure - Google Patents

Abstract

The present invention relates to a method for implementing an automatic exposure, which comprises the following steps: step A, whether the brightness value of a current image is within an expected image brightness threshold value is judged; if the brightness value of the current image is within the threshold value, an imager realizes an exposure according to the exposure time and the electrical gain value of the current image; the step B is continued; step B, a parameter value is confirmed according to the brightness value, the exposure time and the electrical gain value of the current image, the expected image brightness threshold value, and a maximum image brightness value which the imager can obtain so that the product of the regulated image exposure time and the regulated electrical gain value is equal to the parameter value; step C, firstly, the regulated electrical gain value is set to be an expected electrical gain value, and the regulated exposure time is calculated; then, the calculated image exposure time is rounded, and the regulated electrical gain value is calculated; step D, the imager realizes the exposure according to the regulated image exposure time and the regulated electrical gain value. The method of the present invention can be adopted for realizing the high-speed automatic exposure.

Description

A kind of automatic exposure implementation method

Technical field

The present invention relates to camera work, refer to a kind of automatic exposure implementation method especially.

Background technology

Along with development of science and technology, digital camera, high-tech products such as camera mobile phone have stepped in people's the life, and a very important function of these products is exactly an automatic exposure function.Automatic exposure function is exactly time shutter and an electron gain of regulating imager (sensor) according to current environment illumination, in the hope of obtaining best exposure effect.

Though technology and material that each cmos imager manufacturer is adopted are all not quite alike, its basic structure is roughly the same, all includes as the lower part:

Optical filter: gather the three primary colours incident light;

Photodiode: with transform light energy is electronics;

Charge/voltage converter: produce voltage signal;

Amplifier: voltage signal is amplified.

Because the different model imager all has difference in above various piece, so we can not make comprehensive analysis.Imager hynix7131gp with Samsung (Samsung) company is an example, and the relation that counts its time shutter and depth of exposure as shown in Figure 1.Three curves among the figure are represented respectively under the situation of electron gain Gain1=0x50, Gain2=0x40, Gain3=0x60, the time shutter of image and the relation curve of depth of exposure, this curve is to obtain some spots according to different time shutter and corresponding depth of exposure value, and again that each is discrete point couples together and obtains.

As can be seen from the figure, the time shutter increases, and the depth of exposure of image is also increasing; But when the time shutter was longer, it is more little to the contribution of imager depth of exposure under the situation of time shutter than weak point that the recruitment of time shutter is compared identical recruitment.

Realize in the prior art that automatic exposure function has following two kinds of methods.

Method one: approximatioss

Realize automatic exposure function, the system that product comprised all must be able to provide a scalar value of the current depth of exposure of reflection, and this value is the basis of realizing automatic exposure function, generally all is to represent depth of exposure with the brightness of image.

As shown in Figure 2, brightness is divided into two zones or three zones, and Ytarget refers to the target image brightness of user or default, and Ycurrent represents current image brightness; Zone between Ytarget-Lock and the Ytarget+Lock is called ' locked ' zone, if current image brightness Ycurrent in this zone, thinks then that the time shutter of imager and electron gain do not need to adjust.Be called the losing lock zone less than Ytarget-Unlock or greater than the zone of Ytarget+Unlock, if current image brightness Ycurrent in these two zones, thinks then that the time shutter of imager and electron gain need to adjust.

(Ytarget-Unlock, Ytarget-Lock) zone and (Ytarget+Lock, Ytarget+Unlock) zone is called transitional region, when Ycurrent when ' locked ' zone enters the zone, system thinks that still current image remains lock-out state, system does not adjust, but when Ycurrent enters transitional region from the losing lock zone, system thinks that current image still needs to gain or the time shutter is regulated, its processing procedure is the same with processing procedure in the losing lock zone, and the purpose that transitional region is set is a number of times of adjusting time shutter and electron gain in order to reduce.

When automatic exposure function will be positioned at the losing lock zone at current image brightness exactly, adjust its electron gain and time shutter, make adjusted brightness of image be positioned at ' locked ' zone.For example: if current Ycurrent＜Ytarget, after just if 1 unit electron gain of electron gain increase being adjusted to maximum, then will increase by 1 unit the time shutter, and electron gain is transferred to minimum, so repeatedly, till the Ycurrent that adjusts the back acquisition enters ' locked ' zone.

Method two: look-up table

Look-up table is a kind of improvement to approximatioss in fact, this method need be used an electron gain reconciliation statement, table look-up according to the difference of the brightness value of time shutter of input imagery and current image and object brightness and to find the step-length of the electron gain that needs adjust, difference is big more, step-length is big more, and the data in the table generally all are empirical datas.The specific implementation of this method is similar to method one, and major different is that the step-length that electron gain is regulated changes, and governing speed ratio method one is fast; Concrete control method, as mentioned above, if Ycurrent＜Ytarget, need to increase electron gain, after electron gain is adjusted to maximum, increase the time shutter, simultaneously electron gain is adjusted to minimum, so repeatedly, enter ' locked ' zone up to current image brightness.

There is following shortcoming in above-mentioned two kinds of prior art automatic explosion methods:

1, regulates the speed slowly: because the adjustment mode is separately to adjust electron gain and time shutter, and need after new setting comes into force, to continue the inquiry depth of exposure to determine whether to do adjustment next time, therefore often need to adjust repeatedly just to make the brightness of image value enter ' locked ' zone.

2, the setting of adjusting to behind the ' locked ' zone often is not best the setting: because electron gain can not increase the entrained quantity of information of image, can both improve the overall brightness effect of image though that is to say electron gain and time shutter, but have only the time shutter could really reflect the entrained quantity of information of image, and the adjustment of approximatioss is to adjust electron gain earlier in proper order, adjust the time shutter again, so when brightness of image enters ' locked ' zone, electron gain may be very big or very little, makes image effect distortion occur in the part.If adjust the time shutter earlier, adjust electron gain again, because the time shutter is not a linear relationship to the variation that image brightness produced, be difficult to grasp, be easy to make image scintillation to occur.

3, often all be empirical data for the table that uses in the look-up table, the sensitometric characteristic of it and imager has very big relation, has significant limitation.

Summary of the invention

The invention provides a kind of fast automatic exposure method, to solve in the prior art automatic exposure slow problem of regulating the speed.

Automatic exposure implementation method provided by the invention comprises:

Steps A, judge whether the present image brightness value is positioned at the desired image brightness value threshold value of setting, if then imager is realized exposure with the time shutter and the electron gain value of present image; Otherwise, continue the following step;

Step B, according to present image brightness value, time shutter and electron gain value, the hi-vision brightness value that desired image brightness value and imager can obtain, determine a parameter value, make the product of adjusted image exposuring time and adjusted electron gain value equal this parameter value, may further comprise the steps:

B1, the time shutter that makes image, electron gain and brightness value satisfy following relational expression:

$Y=M(1-e^{-\frac{\mathrm{KGx}}{M}})$ Formula (1)

In the formula

Y: the image brightness value that the expression imager obtains;

M: the highest image brightness value that the expression imager can obtain;

K: when representing that the time shutter is 1 unit interval, the image brightness that imager obtains;

G: expression electron gain;

X: expression time shutter;

B2, the time shutter of establishing present image are T1, and electron gain is G1, and brightness value is Y1; The time shutter of adjusting the back image is T2, and electron gain is G2, and brightness value is Y2; According to above-mentioned formula (1), can obtain:

$\frac{\ln \left({M-Y}_1\right)-\ln \left(M\right)}{\ln \left({M-Y}_2\right)-\ln \left(M\right)}=\frac{G_1{T}_1}{G_2{T}_2}$ Formula (2)

B3, adjusted brightness of image value Y2 is made as desired image brightness value Y _Target, the above-mentioned formula of substitution (2) calculates parameter value C:

$C=G_1*T_1*\frac{\ln (M-Y_{t\arg \mathrm{et}})-\ln \left(M\right)}{\ln \left({M-Y}_1\right)-\ln \left(M\right)};$

Step C, earlier adjusted electron gain value is made as the electron gain value of expectation, calculates adjusted image exposuring time; Again the image exposuring time that calculates is rounded, calculate adjusted electron gain value;

Step D, imager are realized exposure with adjusted image exposuring time and adjusted electron gain value.

Described desired images brightness value value is 1/2 of visual maximum brightness, and its optimal threshold value is 1/16 of visual maximum brightness.

The best value of the electron gain value of described expectation is 1 multiplication benefit.

The method of rounding of described image exposuring time is a rounding-off method.

Adopt the inventive method can once approach time shutter and electron gain accurately, realize fast automatic exposure.

Description of drawings

Fig. 1 is the coordinate diagram that concerns of time shutter and depth of exposure;

Fig. 2 is that approximatioss is adjusted synoptic diagram in the prior art;

Fig. 3 is that incident light and exposure concern synoptic diagram;

Fig. 4 is the inventive method process flow diagram.

Embodiment

Referring to Fig. 3, for incident light and exposure concern synoptic diagram.As seen from the figure, the voltage signal of incident light through obtaining amplifying behind the imager, the voltage signal of this amplification and incident light intensity are linear.When environment does not change, how to determine a suitable exposure, make the brightness of image that obtains approach the brightness value of expectation, this is a problem to be solved by this invention.That is to say that the mathematical model that need to determine a voltage transitions be exposure makes exposure after the conversion satisfy the requirement of brightness of image.

The present invention describes relation between the image brightness that electron gain, time shutter and imager obtain with following mathematical model relational expression:

$Y=M(1-e^{-\frac{\mathrm{KGx}}{M}})$ Formula 1;

Y: the image brightness that the expression imager obtains;

M: the highest image brightness that the expression imager can obtain, this is the value of a quantification, different imagers can have different values;

K: when representing that the time shutter is 1 unit interval, the image brightness that imager obtains;

X: expression time shutter;

G: expression electron gain.

Brightness of image value and the test result table of comparisons of following table one for using the above-mentioned relation formula to calculate:

Table one:

Time shutter		1	2	3	4	5	6	7	8	9
											For the first time	Test result	33	67	90	110	128	143	157	169	180
Model value	33	62	91	111	129	144	157	170	180
										For the second time		Test result	30	62	86	105	121	134	146	156	166
Model value	30	56	85	106	123	137	148	159	168
											For the third time	Test result	37	73	99	118	133	146	159	172	183
Model value	37	69	99	122	138	151	162	173	184

The extraordinary test result of approaching of above-mentioned as can be seen from the above table mathematical model.

Have according to formula 1:

$M-Y=M{e}^{\frac{\mathrm{KGx}}{M}}$ Formula 2

Right logarithm is taken from both sides, has:

$\ln (M-Y)-\ln \left(M\right)=\frac{\mathrm{KGx}}{M}$ Formula 3

Suppose present image brightness Y1, the time shutter is T1, and electron gain is G1; Adjusted image brightness is Y2, and the time shutter is T2, and electron gain is G2;

Substitution formula 3 has:

$\ln \left({M-Y}_1\right)-\ln \left(M\right)=\frac{{\mathrm{KG}}_1{T}_1}{M}$ Formula 4

$\ln \left({M-Y}_2\right)-\ln \left(M\right)=\frac{{\mathrm{KG}}_2{T}_2}{M}$ Formula 5

Formula 4 has divided by formula 5:

$\frac{\ln \left({M-Y}_1\right)-\ln \left(M\right)}{\ln \left({M-Y}_2\right)-\ln \left(M\right)}=\frac{G_1{T}_1}{G_2{T}_2}$ Formula 6

Order:

$g\left(Y_1\right)=\frac{\ln (M-Y_1)-\ln \left(M\right)}{\ln \left({M-Y}_1\right)-\ln \left(M\right)}$ Formula 7

Then have:

$T_2=\frac{G_1*T_1}{g\left(Y_1\right)*G_2}$ Formula 8

$G_2=\frac{G_1*T_1}{g\left(Y_1\right)*T_2}$ Formula 9

The purpose of automatic exposure is exactly:

Known, T1, G1, Y1,

Obtain T2, G2 satisfies Y2 in certain threshold range of brightness of image expectation value (Ytarget).

The image brightness scope of supposing expectation is [Ytarget-Threshold, Ytarget+Threshold], and wherein Threshold represents threshold range; The expectation electron gain is Gtarget; According to the mathematical formulae that above-mentioned derivation is come out, fast automatic exposure method flow process of the present invention comprises the steps: as shown in Figure 4

Step 1: judge whether the present image brightness value is positioned at the desired image brightness value threshold value of setting, if, then not needing to start and carry out electron gain and time shutter adjustment process, imager is realized exposure with the time shutter and the electron gain value of present image; Otherwise, continue the following step;

Step 2: with Y ₂=Y _TargetSubstitution formula 7 calculates g (Y1);

Step 3: with G ₂=G _TargetSubstitution formula 8 calculates T ₂

Step 4: with T ₂Round substitution formula 9 and calculate G ₂

Imager is with the time shutter T of the image that calculates ₂With electron gain value G ₂Realize exposure.

Because electron gain G ₂Can not increase the information that imager obtains image, so G ₂Value can not be too big, generally should be between 1-2.

Because the needs of Design of Digital Circuit are as the T that mentions in the explanation of front, G, the relation of Y, T ₂, G ₂Value can have quantization error, so need execution in step three and step 4, result of calculation is carried out back substitution.

The general value of above-mentioned desired images brightness value is 1/2 of a maximum brightness value, and its optimal threshold value is 1/16.

The best value of the electron gain value of above-mentioned expectation is a multiplication benefit.

The method of rounding of described image exposuring time is a rounding-off method.

As seen from the above description, adopt method of the present invention only to need once to adjust and just can approach time shutter and electron gain accurately, therefore, the present invention can realize fast automatic exposure.

In addition, once be out of shape, can obtain: time shutter T by above-mentioned formula 8 ₂With electron gain value G ₂Product equal a parameter value C:

$C=G_1*T_1*\frac{\ln (M-Y_{t\arg \mathrm{et}})-\ln \left(M\right)}{\ln \left({M-Y}_1\right)-\ln \left(M\right)};$

That is to say, after setting the brightness value of adjusted brightness of image value for expectation, the time shutter T that need ask for ₂With electron gain value G ₂Inversely proportional funtcional relationship.C value acquiring method disclosed by the invention is according to present image brightness value, time shutter and electron gain value, and the hi-vision brightness value that desired image brightness value and imager can obtain is determined.

The above; only for the preferable embodiment of the present invention, but protection scope of the present invention is not limited thereto, and anyly is familiar with those skilled in the art in the technical scope that the present invention discloses; the variation that can expect easily or replacement all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection domain of claims.

Claims (4)

1, a kind of automatic exposure implementation method is characterized in that: comprise the following steps:

Steps A, judge whether the present image brightness value is positioned at the desired image brightness value threshold value of setting, if then imager is realized exposure with the time shutter and the electron gain value of present image; Otherwise, continue the following step;

Step B, according to present image brightness value, time shutter and electron gain value, the hi-vision brightness value that desired image brightness value and imager can obtain, determine a parameter value, make the product of adjusted image exposuring time and adjusted electron gain value equal this parameter value, specifically comprise:

B1, the time shutter that makes image, electron gain and brightness value satisfy following relational expression:

$Y=M(1-e^{-\frac{\mathrm{KGx}}{M}})$ Formula (1)

In the formula (1)

Y: the image brightness value that the expression imager obtains;

M: the highest image brightness value that the expression imager can obtain;

K: the expression time shutter is 1 unit interval, when this is the minimum step of time shutter, and the image brightness that imager obtains;

G: expression electron gain;

X: expression time shutter;

B2, the time shutter of establishing present image are T1, and electron gain is G1, and brightness value is Y1; The time shutter of adjusting the back image is T2, and electron gain is G2, and brightness value is Y2; According to above-mentioned formula (1), can obtain:

$\frac{\ln (M-Y_1)-\ln \left(M\right)}{\ln (M-Y_2)-\ln \left(M\right)}=\frac{G_1{T}_1}{G_2{T}_2}$ Formula (2)

B3, adjusted brightness of image value Y2 is made as desired image brightness value Y _Target, the above-mentioned formula of substitution (2) calculates parameter value C:

$C=G_1*T_1*\frac{\ln (M-Y_{t\arg \mathrm{et}})-\ln \left(M\right)}{\ln (M-Y_1)\ln \left(M\right)};$

Step C, earlier adjusted electron gain value is made as the electron gain value of expectation, calculates adjusted image exposuring time; Again the image exposuring time that calculates is rounded, calculate adjusted electron gain value;

Step D, imager are realized exposure with adjusted image exposuring time and adjusted electron gain value.

2, automatic exposure implementation method as claimed in claim 1 is characterized in that: described desired images brightness value value is 1/2 of visual maximum brightness, and its optimal threshold value is 1/16 of visual maximum brightness.

3, automatic exposure implementation method as claimed in claim 1 is characterized in that: the best value of the electron gain value of described expectation is 1 multiplication benefit.

4, automatic exposure implementation method as claimed in claim 1 is characterized in that: the method for rounding of described image exposuring time is a rounding-off method.

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