CN113298729B - Rapid single image defogging method based on minimum value channel - Google Patents
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Abstract
A rapid single image defogging method based on a minimum value channel relates to the technical field of digital image processing and solves the problems of inaccurate estimation of local transmittance and high calculation complexity in the existing defogging restoration method. The method utilizes the guide filtering to carry out smooth filtering processing on the transmittance image, namely, the transmittance can be accurately estimated, the algorithm processing effect is good, the operand is small, and the method can be applied to a real-time engineering system.
Description
Technical Field
The invention relates to the technical field of digital image processing, in particular to a rapid single image defogging method based on a minimum value channel.
Background
The visible light imaging system is affected by haze weather, so that image information acquired by the imaging sensor is seriously degraded, and the utility of outdoor imaging equipment is limited to a great extent. The application value of the image. How to improve the quality of haze degraded images and increase the visibility of the images is a leading topic of common concern in the fields of image processing and computer vision, and especially becomes a hot spot of current research aiming at the quality improvement of single images. Currently, solutions to such problems can be generalized to non-model and model based defogging methods. The non-model-based method mainly improves the visual effect of the image in foggy days, such as histogram equalization, gamma correction, and Retinex algorithm based on color constancy, and although such algorithms are simple and fast, the loss of other information is usually caused while the detailed information of the image is enhanced. The defogging method based on the physical model is established based on an imaging degradation model, and the non-fitness of the atmospheric transmission and the environmental illumination estimation solution in the atmospheric scattering model is converted into the fitness through a plurality of prior information, such as dark primary color prior, geometric prior and the like.
He and the like put forward a dark primary color principle through statistics of outdoor scene images, and realize recovery of the scene through solving a scene dark channel, and the algorithm obtains a good defogging effect, but has high complexity; fattal assumes that the albedo of a local region in an image is a constant, and independent component analysis is adopted to solve the scene albedo, but the influence of image statistical characteristics on algorithm processing results is large; tan utilizes a Markov random field to restrain the image contrast and other characteristics of the outdoor scene according to the prior assumption of the image contrast and the like of the outdoor scene, solves the atmospheric light attenuation term in the model, can better recover the scene information in the image, but the color of the recovered scene is easy to have the oversaturation phenomenon. It can be seen that when some prior assumptions are not satisfied, a significant deviation occurs in the estimation of the local atmospheric transmittance, which causes color distortion, unclear restoration of image details and halo phenomenon in the defogged image. In addition, the high complexity of the algorithm also limits the application of the algorithm in practical engineering.
Disclosure of Invention
The invention provides a rapid single image defogging method based on a minimum channel, aiming at solving the problems of inaccurate estimation of local transmittance and high calculation complexity in the existing defogging restoration method.
A rapid single image defogging method based on a minimum value channel is realized by the following steps:
step one, carrying out transmittance estimation on an imaging model based on atmospheric scattering to obtain a transmittance estimation value
Represented by the formula:
in the formula (I), the compound is shown in the specification,
for the minimum channel image of a foggy scene,
the atmospheric light value is the atmospheric light value of the minimum channel, c is one color channel in the r, g and b channels, and omega and sigma are adjusting constants;
the minimum channel image of the fog-free scene is obtained;
step two, adopting the minimum value channel image of the foggy scene
Minimum value channel image for fog-free scene
The estimation is carried out, namely:
and
the relationship is expressed as a quadratic function combination by the following formula:
in the formula, the vertex of the quadratic function is (I)ave，n)，IaveMean of foggy images, m1And m2Is a quadratic coefficient;
step three, selecting
The first 0.1% of the maximum value of (c) as the region omega of the atmospheric light value calculationJ，
The total pixel number is N, and a corresponding area foggy image I is calculatedc(x) Has a mean value of the gray levels of three channels of AcThen, the gray level average A of the three channels is obtainedcIs taken as the atmospheric light value
Is expressed by the following formula:
step four, obtaining the minimum value channel image of the fog-free scene according to the quadratic function combination form in the step two
Will be provided with
Substituting the transmittance estimated value into the first step
Obtaining an estimated value of transmittance
Smoothing by adopting smoothing filtering to obtain the transmittance t (x);
and step five, restoring the fog-free scene according to an imaging model of atmospheric scattering, wherein the fog-free scene is expressed by the following formula:
in the formula, t0For the adjustment amount, i (x) is a fog scene image, and j (x) is a fog-free scene image.
The invention has the beneficial effects that: the method of the invention establishes an estimation model of the transmittance through the fog image and the fog-free image to the minimum channel, and obtains the minimum channel of the fog-free image through a quadratic function transformation model, thereby obtaining a transmittance map.
The method utilizes the guide filtering to carry out smooth filtering processing on the transmittance image, namely, the transmittance can be accurately estimated, the algorithm processing effect is good, the operand is small, and the method can be applied to a real-time engineering system.
Drawings
FIG. 1 is a graph of z versus y when n takes on different values;
FIG. 2 is IaveWhen different values are taken, a relation graph of z and y is obtained;
FIG. 3 is a diagram showing the effect of the defogging process; wherein, (a) is the minimum value channel image of the foggy scene
The (b) is a minimum value channel image of the fog-free scene
The effect graph of (c) is a transmittance estimated value
The subsequent effect graph, (d) is an effect graph of transmittance t (x) after guiding filtering smoothing;
FIG. 4 is a diagram showing the effect of the defogging treatment; wherein, (a) is the original image, (b) is the effect picture of the dark channel prior result, and (c) is the effect picture processed by the method of the invention.
Detailed Description
The embodiment is described with reference to fig. 1 to 4, and a method for defogging a single image based on a minimum value channel includes:
1. atmospheric scattering model:
at present, the widely used fog imaging model is derived from narasimahan and Nayar based on McCartney attenuation model and atmospheric light model, and the atmospheric scattering based imaging model is shown as follows:
I(x)＝J(x)t(x)+A(1-t(x)) (1)
wherein, i (x) is a foggy scene image, j (x) is a fogless scene image, a is global atmospheric light, and t (x) is atmospheric transmittance.
2. Establishing a transmittance estimation model:
performing minimum value filtering on the local region of equation (1) to obtain a rough estimation of transmittance:
wherein the content of the first and second substances,
for the minimum channel image of a foggy scene,
the atmospheric light values for the minimum channel, ω and σ, are tuning constants.
Is a minimum value channel image of a fog-free scene, but
Is an unknown quantity, and we will now describe the use of a known quantity
For unknown quantity
A method of performing the estimation.
3. Establishing a nonlinear model:
will be provided with
And
carrying out normalization processing, and under the fog condition, carrying out the minimum value channel of the fog-free image
Following a foggy image
Is enlarged by increasing, and is provided with
Therefore, in the present embodiment, a non-linear increasing function relationship is assumed to exist between the two.
In general, a hazy image increases with scene depth,
becoming progressively larger. Through a large number of experiments, it is found that
Smaller, indicating less affected by the fog,
the speed increasing gradually becomes smallerNamely, the slope of the curve becomes smaller; mean value of fog image is IaveWhen is coming into contact with
When the position of the mobile phone is close to the base station,
the speed increasing is minimum, namely the slope of the curve is minimum; with following
The increase in the amount of the mist indicates that the effect of the mist is increased,
the increasing speed is gradually larger, namely the slope of the curve is increased. As can be seen,
and
is a piecewise functional relationship, given in this embodiment
And
the relation is shown in formula (3).
The formula (3) is a quadratic function combination form, and the vertex of the piecewise quadratic function is (I)aveN). Because of the fact that
By using the boundary condition, when
When the temperature of the water is higher than the set temperature,
m is obtained from the formula (3)1＝-n/(Iave)2. When in use
When the temperature of the water is higher than the set temperature,
m is obtained from the formula (3)2＝(1-n)/(1-Iave)2。
From the above analysis, m1＞0，m2＜0。m1And m2The coefficient is a quadratic term coefficient, the slope change of the control curve is larger, the rising speed of the curve is higher, and the slope change is larger.
When in use
The slope of the quadratic function is then:
when in use
When the slope takes the maximum value, kmax＝2n/IaveFrom the above analysis, it can be seen that the slope should be less than 1, and that n ≦ Iave/2. When I isaveWhen n is 0.5, n is 0.1, 0.2, 0.25, 0.3, and the model established by the formula (3) shows that n is 0.1, 0.2, 0.25, 0.3
The corresponding z to y relationship is then as shown in figure 1. Average value of general foggy image IaveThe larger the fog density of the imaging scene; conversely, the fog density of the imaged scene is smaller. When the value of n is smaller, the area enclosed by the curve and the straight line y which is z is larger, and the method is suitable for processing the image with larger fog concentration; conversely, when the value of n is larger, the area enclosed by the curve and the straight line y ═ z is smaller, and the area is smallerIt is suitable for processing images with low fog density. Then n and IaveThe relationship of (1): n ═ Iave/2-0.05. When I isaveValues are respectively Iave＝0.3、Iave＝0.4、Iave＝0.5、Iave0.6 is given
The corresponding z to y relationship is then as shown in figure 2.
4. Obtaining the transmittance;
selecting
The area in which the first 0.1% of the pixels of the maximum value of (A) are calculated as the atmospheric light value is
The total number of pixels is N, and the corresponding fog image I is calculatedc(x) Has a mean value of the gray levels of three channels of AcThen, three channels A are obtainedcIs taken as the atmospheric light value
The expression of (c) is as follows.
5. Restoring the image;
according to the model established by the formula (3), the minimum channel of the fog-free scene of the image can be obtained
Will be provided with
And the equation (5) is substituted into the transmittance estimation model equation (2) to obtain the transmittance estimation value
Using smoothing filtering (e.g. guided filtering)Gaussian filtering, bilateral filtering, etc.) to obtain t (x). And then, restoring the fog-free scene according to an atmospheric scattering model, wherein the formula is as follows:
in the formula, t0In the present embodiment, the adjustment amount is set to 0.01. The image restored by the above method is generally darker and is enhanced by an automatic color gradation method. The processing results are shown in fig. 4.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (3)
1. The rapid single image defogging method based on the minimum value channel is characterized by comprising the following steps: the method is realized by the following steps:
step one, carrying out transmittance estimation on an imaging model based on atmospheric scattering to obtain a transmittance estimation value
Represented by the formula:
in the formula (I), the compound is shown in the specification,
for the minimum channel image of a foggy scene,
the atmospheric light value is the atmospheric light value of the minimum channel, c is one color channel in the r, g and b channels, and omega and sigma are adjusting constants;
the minimum channel image of the fog-free scene is obtained;
step two, adopting the minimum value channel image of the foggy scene
Minimum value channel image for fog-free scene
The estimation is carried out, namely:
and
the relationship is expressed as a quadratic function combination by the following formula:
in the formula, the vertex of the quadratic function is (I)ave，n)，IaveMean of foggy images, m1And m2Is a quadratic coefficient;
step three, selecting
The first 0.1% of the maximum value of (c) as the region omega of the atmospheric light value calculationJ，
The total pixel number is N, and a corresponding area foggy image I is calculatedc(x) Has a mean value of the gray levels of three channels of AcThen, the gray level average A of the three channels is obtainedcIs taken as the atmospheric light value
Is expressed by the following formula:
step four, obtaining the minimum value channel image of the fog-free scene according to the quadratic function combination form in the step two
Will be provided with
Substituting the transmittance estimated value into the first step
Obtaining an estimated value of transmittance
Smoothing by adopting smoothing filtering to obtain the transmittance t (x);
and step five, restoring the fog-free scene according to an imaging model of atmospheric scattering, wherein the fog-free scene is expressed by the following formula:
in the formula, t0To adjust the amount.
2. The method for defogging a single image based on a minimum value channel according to claim 1, wherein: in the second step:
when in use
When the temperature of the water is higher than the set temperature,
m can be obtained according to a quadratic function formula1＝-n/(Iave)2；
When in use
When the temperature of the water is higher than the set temperature,
can obtain m2＝(1-n)/(1-Iave)2；
Finally, the following can be obtained: m is1＞0，m2＜0；
When in use
The slope k of the quadratic function is then:
when in use
When the slope takes the maximum value, kmax＝2n/Iave。
3. The method for defogging a single image based on a minimum value channel according to claim 1, wherein: and step five, performing enhancement processing on the restored image by adopting an automatic color gradation method.
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