CN113850743B - Video global tone mapping method based on self-adaptive parameters - Google Patents
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Abstract
The invention discloses a video global tone mapping method based on self-adaptive parameters, which adopts a global tone mapping function f (lum + ∂) to process video images frame by frame, wherein the self-adaptive parameters ∂ in the global tone mapping function change along with each frame of image, and the confirming method comprises the following steps: firstly, acquiring a brightness average value of an image; then, an offset parameter a = ln [ (lum) is determined from the luminance average valuemean+1)/(0.5+1)](ii) a And determining a proportion parameter b according to the offset parameter a to finally obtain an adaptive parameter ∂ = a × b. And (3) processing the video image frame by adopting a global tone mapping function f (lum + ∂), and converting the video image into three-channel RGB data to obtain a low dynamic range image. The invention adds the number ∂ which is adaptively changed according to the brightness of the current frame to quickly adjust the prior tone mapping method, thereby solving the problem of detail loss caused by the instantaneous change of the brightness of the image in the prior method.
Description
Technical Field
The invention relates to a video global tone mapping method based on self-adaptive parameters.
Background
The tone mapping algorithm is to compress the display luminances of the HDR image into the display range of the LDR device, while keeping important information such as details and colors of the image during the conversion. The tone mapping algorithm needs to have two basic functions: 1. compressing the image brightness; 2. and the details and the color of the image are kept, so that important information is prevented from being lost.
The range of luminances of an LDR display device is much smaller than the HDR image, for which the luminance values represent absolute luminance values, and in nature. Since the luminance range of the HDR display device is large enough, the luminance value recorded by each pixel of the HDR image is the luminance value displayed on the HDR display device. LDR images differ in that the LDR display devices have a small luminance range, and display ranges of only 0-255, so that the range of colors and luminances that can be displayed is limited. In order to make reasonable use of the limited luminance space, the luminance of the LDR image does not actually correspond to the luminance in the displayed scene, but is a relative luminance. Some high-quality global tone mapping algorithms, such as an ACES tone mapping algorithm and a film tone mapping algorithm, need to adjust partially adjustable parameters in the algorithm according to the brightness of an actual image before processing the image, and then perform mapping processing on the image. However, images in a video are changed from frame to frame, and the brightness difference of the images in a short time under the same environment is generally not large, if special conditions such as: the object blocks the whole dark of the sunlight image; when sunlight is exposed in rainy days and sunny days, the image becomes bright as a whole, which may cause the global tone mapping algorithm for the previous environment, which has adjusted parameters, to lose part of details when processing the current image, and affect the quality of the image.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the prior art, the video global tone mapping method based on the self-adaptive parameters is provided, and in the video tone mapping process, the parameters are changed according to the brightness of the current frame, so that the algorithm is quickly adjusted, and the problem of detail loss caused by instantaneous change of the image brightness is solved.
The technical scheme is as follows: a video global tone mapping method based on adaptive parameters adopts a global tone mapping function f (lum + ∂) to process video images frame by frame, the global tone mapping function f (lum + ∂) comprises adaptive parameters ∂, and the method for confirming the adaptive parameters ∂ along with each frame of image comprises the following steps:
step 1: obtaining the average value of brightness lum of the imagemean；
Step 2: determining an offset parameter a, a = ln [ (lum)mean+1)/(0.5+1)]；
And step 3: determining a proportional parameter b when the offset parameter a>0, b = lumldrWherein lumldr=f(lumwdr) Wide dynamic range luminance data lum representing a picturewdrSubstitution into the low dynamic range luminance calculated by the existing global tone mapping function f (lum)Degree data; when the offset parameter a<0, b =1-lumldr；
And 4, step 4: obtaining an adaptive parameter ∂ = a × b according to the offset parameter a and the proportional parameter b;
and (3) processing the video image frame by adopting a global tone mapping function f (lum + ∂), and converting the video image into three-channel RGB data to obtain a low dynamic range image.
Further, the step 1 comprises the following specific steps:
step 1.1: converting the wide dynamic RGB three-channel pixel value into a single-channel brightness value lum, and converting the wide dynamic range brightness data lum of the picturewdr= lum/256, and the number of brightness value data is recorded as W;
step 1.2: filtering out the brightest percentage of the luminance datal 1And the darkest percentl 2The number of the remaining luminance data is denoted as W1=(1-0.01*l 1-0.01*l 2) W, maximum value in the residual luminance data is recorded as lummax；
Step 1.3: normalizing and averaging the filtered luminance data:
wherein, lumwdr(i) Indicating the luminance value of each of the remaining luminance data.
Has the advantages that: the video global tone mapping method based on the self-adaptive parameters is based on the existing global tone mapping algorithm, and the number ∂ which is changed in a self-adaptive manner according to the brightness of the current frame is added in the video tone mapping process to quickly adjust the algorithm, so that the problem of detail loss caused by the instantaneous change of the brightness of the image in the existing global tone mapping algorithm is solved.
Drawings
FIG. 1 is a flow chart of the present method;
fig. 2 is a tone mapping graph.
Detailed Description
The invention is further explained below with reference to the drawings.
As shown in fig. 1, in a video global tone mapping method based on adaptive parameters, a global tone mapping function f (lum + ∂) is used to process video images frame by frame, so as to solve the problem of detail loss caused by instantaneous change of image brightness when the existing global tone mapping algorithm is used, the global tone mapping function f (lum + ∂) includes adaptive parameters ∂, and the adaptive parameters ∂ are dynamically adjusted along with each frame of image.
The dynamic confirmation method of the adaptive parameter ∂ comprises the following steps:
step 1: obtaining the average value of brightness lum of the imagemeanThe method specifically comprises the following substeps:
step 1.1: converting a wide dynamic RGB three-channel pixel value into a single-channel brightness value lum, wherein the value range of the data is determined by the number of bits of wide dynamic image data, and the value range is generally 0 to (2)10-1) or 0 to (2)12-1) for easy calculation, recording wide dynamic range luminance data lumwdrNumber of luminance value data is represented as W, = lum/256.
Step 1.2: to avoid the influence of the original image defects on tone mapping, the brightest percentage of the brightness data is filteredl 1And the darkest percentl 2The data of (a) to (b) to (c),l 1andl 1usually 1-5, the number of the residual brightness data is recorded as W1=(1-0.01*l 1-0.01*l 2) W, maximum value in the residual luminance data is recorded as lummax。
Step 1.3: normalizing and averaging the filtered luminance data:
wherein, lumwdr(i) Indicating the luminance value of each of the remaining luminance data. Mean value of brightness lum of imagemeanThe range of (1) is 0-1, and the method is used for subsequently judging the brightness distribution of the image.
Step 2: an offset parameter a is determined.
Wide dynamic range luminance data lum of picturewdrThe low dynamic range luminance data lum can be calculated by substituting the existing global tone mapping function f (lum)ldrInstant lumldr=f(lumwdr) The tone mapping curve is shown in fig. 2, where the horizontal axis represents the image-wide dynamic luminance value and the vertical axis represents the low dynamic luminance value after mapping. Normalized luminance mean value lum obtained in step 1meanAs can be seen, the following three situations exist in the image: the first expression is as follows: lummean>At 0.5, the entire image appears as more dots with relatively large brightness; performing two steps: lummean<At 0.5, the entire image appears as more dots of relatively small brightness; the third expression is that: lummeanWhen =0.5, the entire image appears uniform in brightness and darkness.
Offset parameter a = ln [ (lum)mean+1)/(0.5+1)]When the image situation is in manifestation, a>0, the tone mapping curve is shown as a dashed line in FIG. 2; when the image situation is in representation two, a<0, the tone mapping curve is shown by the dotted line in FIG. 2; when the image condition is expressed in three, a =0, the original algorithm is unchanged, that is, the existing global tone mapping function f (lum) is directly adopted to obtain the low dynamic range image, and the tone mapping curve is shown as a solid line in fig. 2. The purpose of parameter 1 used in offset parameter a is to prevent the value of a from being too large, which affects the tone mapping effect.
And step 3: and determining a proportion parameter b.
When the offset parameter a>When 0, the whole image is slightly bright, the part with high brightness in the image is important information, the offset of the curve in a high-brightness area is adjusted and reduced through a proportion parameter b, namely, the loss of high-brightness detail information is reduced, and b = lumldr。
When the offset parameter a<When 0, the whole image is dark, the part with low brightness in the image is important information, the offset of the curve in the low brightness area is reduced by adjusting the proportion parameter b, namely, the loss of the detail information of the low brightness is reduced, and b =1-lumldr。
And 4, step 4: obtaining an adaptive parameter ∂ = a × b according to the offset parameter a and the proportional parameter b;
parameter(s)∂ acting on the existing global tone mapping function, i.e. outputting a low dynamic range luminance lumldr-∂=f(lumwdr+ ∂) as horizontal shift ∂ of tone mapping curve horizontal axis, finally converting into three-channel RGB data to obtain low dynamic range image.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (2)
1. A video global tone mapping method based on self-adaptive parameters is characterized in that a global tone mapping function f (lum) is adoptedwdr+ ∂) the global tone mapping function f (lum) processes the video image frame by framewdr+ ∂) includes adaptive parameter ∂, and the method for confirming the adaptive parameter ∂ with each frame of image includes:
step 1: obtaining the average value of brightness lum of the imagemean；
Step 2: determining an offset parameter a, a = ln [ (lum)mean+1)/(0.5+1)]；
And step 3: determining a proportional parameter b when the offset parameter a>0, b = lumldrWherein lumldr=f(lumwdr) Wide dynamic range luminance data lum representing a picturewdrSubstituting into the existing global tone mapping function f (lum)wdr) (ii) calculated low dynamic range luminance data; when the offset parameter a<0, b =1-lumldr；
And 4, step 4: obtaining an adaptive parameter ∂ = a × b according to the offset parameter a and the proportional parameter b;
using a global tone mapping function f (lum)wdr+ ∂) processing the video image frame by frame, then converting into three-channel RGB data to obtain low dynamic range image.
2. The adaptive parameter based video global tone mapping method according to claim 1, wherein the step 1 comprises the following specific steps:
step 1.1: converting the wide dynamic RGB three-channel pixel value into a single-channel brightness value lum, and converting the wide dynamic range brightness data lum of the picturewdr= lum/256, and the number of brightness value data is recorded as W;
step 1.2: filtering out the brightest percentage of the luminance datal 1And the darkest percentl 2The number of the remaining luminance data is denoted as W1=(1-0.01*l 1-0.01*l 2) W, maximum value in the residual luminance data is recorded as lummax；
Step 1.3: normalizing and averaging the filtered luminance data:
wherein, lumwdr(i) Indicating the luminance value of each of the remaining luminance data.
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| CN109410126A (en) * | 2017-08-30 | 2019-03-01 | 中山大学 | A kind of tone mapping method of details enhancing and the adaptive high dynamic range images of brightness |
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| EP3324629B1 (en) * | 2014-05-28 | 2019-06-19 | Koninklijke Philips N.V. | Methods and apparatuses for encoding an hdr images, and methods and apparatuses for use of such encoded images |
| GB201410635D0 (en) * | 2014-06-13 | 2014-07-30 | Univ Bangor | Improvements in and relating to the display of images |
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| EP3220349A1 (en) * | 2016-03-16 | 2017-09-20 | Thomson Licensing | Methods, apparatus, and systems for extended high dynamic range ("hdr") hdr to hdr tone mapping |
| US10074162B2 (en) * | 2016-08-11 | 2018-09-11 | Intel Corporation | Brightness control for spatially adaptive tone mapping of high dynamic range (HDR) images |
| EP3312798A1 (en) * | 2016-10-20 | 2018-04-25 | Thomson Licensing | Method and device for inverse tone mapping |
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