CN103595934A - Method for solving smear problem during frame transfer CCD continuous scanning - Google Patents

Abstract

The invention provides a method for solving the smear problem during frame transfer CCD continuous scanning, belongs to the technical field of frame transfer CCD image processing, and aims to solve the problems that in the prior art, a dark pixel area needs to be additionally arranged on a CCD and smear information of the dark pixel area is much affected by noise. The method comprises the following steps: step 1, a CCD image signal is preprocessed; step 2, an equation set of smear increments in the operating mode of frame transfer CCD continuous scanning is established; step 3, the smear increments are obtained; step 4, the smear problem is solved. The smear problem is solved in the operating mode of frame transfer CCD continuous scanning through the four steps. Experiments verify that computational accuracy of the smear increments can reach 1% and the genuine CCD image signal can be effectively restored. The method for solving the smear problem during frame transfer CCD continuous scanning is simple, easy to implement, high in adaptability, and high in accuracy.

Description

The modification method of frame transfer CCD smear problem when continuous sweep

Technical field

The present invention relates to the modification method of a kind of frame transfer CCD smear problem when continuous sweep, belong to frame transfer ccd image process field technology.

Background technology

Smear phenomenon is a kind of inherent characteristic of frame transfer CCD, and it refers to after charge accumulated process completes, and transfers to the still ceaselessly sensitization and produce electric charge again of Shi， photosensitive area, memory block, and then pollute already present electric charge by photosensitive area.Conventionally the elimination adopting or the method that weakens the impact of smear phenomenon are: the one, and add mechanical shutter and avoid the continuous sensitization in imaging area; The 2nd, adopt increase time for exposure or auto iris to slacken smear impact; The 3rd, utilize dark pixel region to extract smear information and eliminate.First two method is only effective to single-frame static images, and needs to increase extra means.Although the third mode can be processed the smear impact of continuous sweep image, need CCD additionally with dark pixel region, and the smear information in dark pixel region is affected by noise larger.

Summary of the invention

In order to overcome the defect of above method, invented a kind of without extra smear testing apparatus, on processing with the frame transfer ccd image signal of smear impact, extracting smear affects increment correction, and then effectively restores real ccd image signal.This method is not only simple, and applicability is strong, and precision is higher.

The correction algorithm that the present invention relates to the smear problem of a kind of frame transfer CCD, comprises the following steps:

Step 1, the preliminary treatment of ccd image signal,

Before smear revises, the picture signal of frame transfer CCD collection illumination is deducted to the back end signal of unglazed photograph, obtain the effective picture signal S (x, y) being produced by illumination completely; Then effective picture signal is carried out to non-linear correction; Obtaining revised effective picture signal is linear with the variation of the time of integration;

Step 2, sets up the equation group of the smear increment under frame transfer CCD continuous sweep working method,

For imaging area not with reset function or do not carry out the frame transfer CCD of reset operation, during m * n frame transfer CCD continuous sweep work, in frame transfer direction, each pixel smear increment of each row is identical, and the smear increment Delta S (x, y) that y is listed as each pixel is:

$\mathrm{\ΔS}(x,y)=\underset{x=1}{\overset{m}{\mathrm{\Σ}}}k{\mathrm{\η}}_1{T}_{\mathrm{ti}}I(x,y)---\left(1\right)$

Wherein, k is proportionality coefficient, η ₁for the photoelectric conversion efficiency in charge transfer process, T _tibe the frame transfer clock cycle, I (x, y) is the radiation intensity that pixel (x, y) is accepted;

The actual signal S (x, y) of each pixel of CCD is:

S(x,y)＝kη ₂T _expI(x,y) （2）

Wherein, η ₂for the photoelectric conversion efficiency in charge accumulated process, T _expit is the time for exposure;

By (1) formula and (2) Shi Ke get:

$\mathrm{\ΔS}(x,y)=\frac{T_{\mathrm{ti}}{\mathrm{\η}}_1}{T_{\exp }{\mathrm{\η}}_2}\underset{x=1}{\overset{m}{\mathrm{\Σ}}}S(x,y)---\left(3\right)$

Ccd image signal S ' (x, y) with smear impact is as the above analysis:

S′(x,y)＝S(x,y)+ΔS(x,y) （4）

Each pixel (x, y) of m * n frame transfer CCD is set up to the equation group that the equation group being comprised of (3) formula and (4) formula is the smear increment of frame transfer CCD under continuous sweep working method, as follows:

$\left\{\begin{array}{c}{S}^{\′}(x,y)=S(x,y)+\mathrm{\ΔS}(x,y)\\ \mathrm{\ΔS}(x,y)=\frac{T_{\mathrm{ti}}{\mathrm{\η}}_i}{T_{\exp }{\mathrm{\η}}_2}\underset{x=1}{\overset{m}{\mathrm{\Σ}}}S(x,y)\end{array}\right.$ (x=1 wherein, 2 ... m; Y=1,2 ... n) (5)

Step 3, solves smear increment,

Y row pixel, following relational expression is set up,

${\mathrm{\ΔS}}^{\′}(x,y)=\frac{T_{\mathrm{ti}}{\mathrm{\η}}_i}{T_{\exp }{\mathrm{\η}}_2}\underset{x=1}{\overset{m}{\mathrm{\Σ}}}{S}^{\′}(x,y)=K\underset{x=1}{\overset{m}{\mathrm{\Σ}}}{S}^{\′}(x,y)---\left(6\right)$

Definition

for smear coefficient, by (5) formula and (6) Shi Ke get:

${\mathrm{\ΔS}}^{\′}(x,y)=K\underset{x=1}{\overset{m}{\mathrm{\Σ}}}[S(x,y)+\mathrm{\ΔS}(x,y)]=K\underset{x=1}{\overset{m}{\mathrm{\Σ}}}S(x,y)+K\underset{x=1}{\overset{m}{\mathrm{\Σ}}}\mathrm{\ΔS}(x,y)=(1+m\×K)\mathrm{\ΔS}(x,y)---\left(7\right)$

By (6) formula and (7) Shi Ke get:

$\mathrm{\ΔS}(x,y)=\frac{K}{(1+m\×K)}\underset{x=1}{\overset{m}{\mathrm{\Σ}}}{S}^{\′}(x,y)---\left(8\right)$

From (8) formula, the smear increment Delta S (x, y) of frame transfer CCD under continuous sweep working method can draw by the ccd image calculated signals with smear impact;

Step 4, carries out smear correction,

The picture signal S (x, y) that can be obtained the revised CCD of smear by (5) formula and (8) formula is:

S(x,y)＝S′(x,y)-ΔS(x,y) （9）

By above-mentioned four steps, completed the correction of the smear problem of frame transfer CCD under continuous sweep working method.

Beneficial effect of the present invention: before carrying out smear correction, the ccd image signal with smear impact is carried out to preliminary treatment, preliminary treatment comprises dark signal deduction and non-linear modification of signals; Smear phenomenon mechanism of production from frame transfer CCD under continuous sweep working method, frame transfer CCD is when continuous sweep working method, the imaging area of frame transfer CCD is not resetted, guaranteed that it is identical that smear that each in frame transfer direction is listed as each pixel affects increment.Therefore the equation group of smear increment that obtains m * n drum-type frame transfer CCD is as follows:

$\left\{\begin{array}{c}{S}^{\′}(x,y)=S(x,y)+\mathrm{\ΔS}(x,y)\\ \mathrm{\ΔS}(x,y)=\frac{T_{\mathrm{ti}}{\mathrm{\η}}_i}{T_{\exp }{\mathrm{\η}}_2}\underset{x=1}{\overset{m}{\mathrm{\Σ}}}S(x,y)\end{array}\right.$ (x=1 wherein, 2 ... m; Y=1,2 ... n)

S ' (x, y) is the signal after smear impact, and S (x, y) is the actual signal without smear impact, T _tithe frame transfer clock cycle, T _expthe time for exposure, η ₁for the photoelectric conversion efficiency in charge transfer process, η ₂for the photoelectric conversion efficiency in charge accumulated process, x, y is respectively the row ordinal sum row ordinal number of pixel; When solving the equation group of smear increment, adopted dexterously cumulative iterative method, make to solve simple and convenient.

In sum, method of the present invention is without any need for extra smear testing apparatus, simple, and has verified that by experiment the method tries to achieve the precision of smear increment and can reach 1%, can effectively restore real ccd image signal.

Accompanying drawing explanation

Fig. 1 is that the field trial of imaging spectrometer ground gathers and pass through pretreated signal graph.

Fig. 2 is the graph of a relation of smear increment size and picture dot row ordinal number.

Fig. 3 is the actual signal figure that removes smear impact.

Embodiment

The modification method of the smear problem under a kind of frame transfer CCD continuous sweep working method of the present invention, concrete enforcement need to following four steps.

1, the preliminary treatment of ccd image signal.

Because the smear of frame transfer ccd image affects increment main and light signal and frame transfer clock Periodic correlation, therefore before smear revises, the back end signal that the picture signal of frame transfer CCD collection illumination is deducted to unglazed photograph, obtains the effective picture signal being produced by illumination completely.Then effective picture signal is carried out to non-linear correction.Obtaining revised effective picture signal is linear with the variation of the time of integration.

As shown in Figure 1, a certain model imaging spectrometer ground field trial gathers and passes through pretreated signal graph, the CCD47-20 planar array detector of the CCDWei e2v company adopting, a wide frame transfer, back lighting type CCD detector, the picture dot number of imaging area is 1024 * 1024 dimensions, and its imaging area does not have reset function.For the ease of observing smear phenomenon, therefore display gray shade value scope is made as to 0-100.Horizontal direction is space dimension, and vertical direction is spectrum dimension (increasing successively for wavelength from top to bottom).Because extreme ultraviolet cannot be detected to vacuum ultraviolet (VUV) band signal in ground, so the signal of part is not useful signal on image, be the invalid signals that smear phenomenon is introduced.

2, set up the equation group of the smear increment under frame transfer CCD continuous sweep working method.

Mechanism of production from the smear phenomenon under frame transfer CCD continuous sweep working method, for imaging area not with reset function or do not carry out the frame transfer CCD of reset operation, during m * n frame transfer CCD continuous sweep work, in frame transfer direction, each pixel smear increment of each row is identical, the smear increment Delta S (x, y) that y is listed as each pixel is:

$\mathrm{\ΔS}(x,y)=\underset{x=1}{\overset{m}{\mathrm{\Σ}}}k{\mathrm{\η}}_1{T}_{\mathrm{ti}}I(x,y)---\left(1\right)$

Wherein, k is proportionality coefficient, η ₁for the photoelectric conversion efficiency in charge transfer process, T _tibe the frame transfer clock cycle, I (x, y) is the radiation intensity that pixel (x, y) is accepted.

Because the actual signal S (x, y) of each pixel of CCD is:

S(x,y)＝kη ₂T _expI(x,y) （2）

Wherein, η ₂for the photoelectric conversion efficiency in charge accumulated process, T _expit is the time for exposure.

By (1) formula and (2) Shi Ke get:

$\mathrm{\ΔS}(x,y)=\frac{T_{\mathrm{ti}}{\mathrm{\η}}_1}{T_{\exp }{\mathrm{\η}}_2}\underset{x=1}{\overset{m}{\mathrm{\Σ}}}S(x,y)---\left(3\right)$

Ccd image signal S ' (x, y) with smear impact is as the above analysis:

S′(x,y)＝S(x,y)+ΔS(x,y) （4）

Each pixel (x, y) of m * n frame transfer CCD is set up to the equation group that the equation group being comprised of (3) formula and (4) formula is the smear increment of frame transfer CCD under continuous sweep working method.As follows:

$\left\{\begin{array}{c}{S}^{\′}(x,y)=S(x,y)+\mathrm{\ΔS}(x,y)\\ \mathrm{\ΔS}(x,y)=\frac{T_{\mathrm{ti}}{\mathrm{\η}}_i}{T_{\exp }{\mathrm{\η}}_2}\underset{x=1}{\overset{m}{\mathrm{\Σ}}}S(x,y)\end{array}\right.$ (x=1 wherein, 2 ... m; Y=1,2 ... n) (5)

3, solve smear increment.

For y row pixel, following relational expression is set up

${\mathrm{\ΔS}}^{\′}(x,y)=\frac{T_{\mathrm{ti}}{\mathrm{\η}}_i}{T_{\exp }{\mathrm{\η}}_2}\underset{x=1}{\overset{m}{\mathrm{\Σ}}}{S}^{\′}(x,y)=K\underset{x=1}{\overset{m}{\mathrm{\Σ}}}{S}^{\′}(x,y)---\left(6\right)$

Definition

for smear coefficient, by (5) formula and (6) Shi Ke get:

${\mathrm{\ΔS}}^{\′}(x,y)=K\underset{x=1}{\overset{m}{\mathrm{\Σ}}}[S(x,y)+\mathrm{\ΔS}(x,y)]=K\underset{x=1}{\overset{m}{\mathrm{\Σ}}}S(x,y)+K\underset{x=1}{\overset{m}{\mathrm{\Σ}}}\mathrm{\ΔS}(x,y)=(1+m\×K)\mathrm{\ΔS}(x,y)---\left(7\right)$

By (6) formula and (7) Shi Ke get:

$\mathrm{\ΔS}(x,y)=\frac{K}{(1+m\×K)}\underset{x=1}{\overset{m}{\mathrm{\Σ}}}{S}^{\′}(x,y)---\left(8\right)$

From (8) formula, the smear increment Delta S (x, y) of frame transfer CCD under continuous sweep working method can draw by the ccd image calculated signals with smear impact.

For the image of m (1024) * n (1024) dimension, its frame transfer clock period T _tibe 10 μ s, gather time for exposure T _expfor 400ms, the photoelectric conversion efficiency η of electric charge transfer and charge accumulated process ₁and η ₂can think to equate.So smear COEFFICIENT K is 2.5 * 10 ^-5.

Because the charge transfer direction of Fig. 1 is vertical direction, so the smear increment of each picture dot is identical in the every row of image, by (8) formula and above-mentioned relevant parameter, obtain the relation of smear increment and row in Fig. 1, as Fig. 2.

4, carry out smear correction.

By (5) formula and (8) Shi Ke get: the picture signal S (x, y) of the revised CCD of smear is:

S(x,y)＝S′(x,y)-ΔS(x,y) （9）

By above-mentioned four steps, completed the correction of the smear problem of frame transfer CCD under continuous sweep working method, Fig. 1 has been carried out to the revised image of smear, as Fig. 3.Experimental verification the computational accuracy of smear increment can reach 1%, can effectively restore real ccd image signal.This method is not only simple, and applicability is strong, and precision is higher.

Claims (1)

1. the modification method of frame transfer CCD smear problem when continuous sweep, is characterized in that, comprises the following steps:

Step 1, the preliminary treatment of ccd image signal,

Before smear revises, the picture signal of frame transfer CCD collection illumination is deducted to the back end signal of unglazed photograph, obtain the effective picture signal S (x, y) being produced by illumination completely; Then effective picture signal is carried out to non-linear correction; Obtaining revised effective picture signal is linear with the variation of the time of integration;

Step 2, sets up the equation group of the smear increment under frame transfer CCD continuous sweep working method,

For imaging area not with reset function or do not carry out the frame transfer CCD of reset operation, during m * n frame transfer CCD continuous sweep work, in frame transfer direction, each pixel smear increment of each row is identical, and the smear increment Delta S (x, y) that y is listed as each pixel is:

$\mathrm{\ΔS}(x,y)=\underset{x=1}{\overset{m}{\mathrm{\Σ}}}k{\mathrm{\η}}_1{T}_{\mathrm{ti}}I(x,y)---\left(1\right)$

Wherein, k is proportionality coefficient, η ₁for the photoelectric conversion efficiency in charge transfer process, T _tibe the frame transfer clock cycle, I (x, y) is the radiation intensity that pixel (x, y) is accepted;

The actual signal S (x, y) of each pixel of CCD is:

S(x,y)＝kη ₂T _expI(x,y) （2）

Wherein, η ₂for the photoelectric conversion efficiency in charge accumulated process, T _expit is the time for exposure;

By (1) formula and (2) Shi Ke get:

$\mathrm{\ΔS}(x,y)=\frac{T_{\mathrm{ti}}{\mathrm{\η}}_1}{T_{\exp }{\mathrm{\η}}_2}\underset{x=1}{\overset{m}{\mathrm{\Σ}}}S(x,y)---\left(3\right)$

Ccd image signal S ' (x, y) with smear impact is as the above analysis:

S′(x,y)＝S(x,y)+ΔS(x,y) （4）

Each pixel (x, y) of m * n frame transfer CCD is set up to the equation group that the equation group being comprised of (3) formula and (4) formula is the smear increment of frame transfer CCD under continuous sweep working method, as follows:

$\left\{\begin{array}{c}{S}^{\′}(x,y)=S(x,y)+\mathrm{\ΔS}(x,y)\\ \mathrm{\ΔS}(x,y)=\frac{T_{\mathrm{ti}}{\mathrm{\η}}_i}{T_{\exp }{\mathrm{\η}}_2}\underset{x=1}{\overset{m}{\mathrm{\Σ}}}S(x,y)\end{array}\right.$ (x=1 wherein, 2 ... m; Y=1,2 ... n) (5)

Step 3, solves smear increment,

Y row pixel, following relational expression is set up,

${\mathrm{\ΔS}}^{\′}(x,y)=\frac{T_{\mathrm{ti}}{\mathrm{\η}}_i}{T_{\exp }{\mathrm{\η}}_2}\underset{x=1}{\overset{m}{\mathrm{\Σ}}}{S}^{\′}(x,y)=K\underset{x=1}{\overset{m}{\mathrm{\Σ}}}{S}^{\′}(x,y)---\left(6\right)$

Definition

for smear coefficient, by (5) formula and (6) Shi Ke get:

${\mathrm{\ΔS}}^{\′}(x,y)=K\underset{x=1}{\overset{m}{\mathrm{\Σ}}}[S(x,y)+\mathrm{\ΔS}(x,y)]=K\underset{x=1}{\overset{m}{\mathrm{\Σ}}}S(x,y)+K\underset{x=1}{\overset{m}{\mathrm{\Σ}}}\mathrm{\ΔS}(x,y)=(1+m\×K)\mathrm{\ΔS}(x,y)---\left(7\right)$

By (6) formula and (7) Shi Ke get:

$\mathrm{\ΔS}(x,y)=\frac{K}{(1+m\×K)}\underset{x=1}{\overset{m}{\mathrm{\Σ}}}{S}^{\′}(x,y)---\left(8\right)$

From (8) formula, the smear increment Delta S (x, y) of frame transfer CCD under continuous sweep working method can draw by the ccd image calculated signals with smear impact;

Step 4, carries out smear correction,

The picture signal S (x, y) that can be obtained the revised CCD of smear by (5) formula and (8) formula is:

S(x,y)＝S′(x,y)-ΔS(x,y) （9）

By above-mentioned four steps, completed the correction of the smear problem of frame transfer CCD under continuous sweep working method.

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