CN101674389A - Method for testing compression history of BMP image based on loss amount of image information - Google Patents

Abstract

The invention relates to a method for testing the compression history of a BMP image based on the loss amount of image information, belonging to the technical field of signal and information processing. The method is characterized by comprising the steps of: under the condition of only obtaining a digital image, cutting the BMP image to be tested into 4 rows and 4 lines; evaluating an original image; compressing the image to be tested and the evaluated original image into two JPEG images, the quality factor of which is 100; extracting the characteristic by comparing the loss amount of the image information of the two JPEG images; and testing the compression history of the large quantities of the images with a Fisher linear classifier in a classifying way, or judging the compression historyof the single BMP image with original compression quality factor by means of threshold value segmentation. The method can exactly identify and prove the compression history of the many or single BMPimage(s). The method is applicable to the field of information security.

Description

The historical detection method of a kind of BMP image compression based on the image information loss amount

Technical field

The invention belongs to the Signal and Information Processing technical field, relate to the digital image evidence collecting method that detects BMP (bitmap) image compression history.

Background technology

Mainly containing two kinds of methods at present detects the compression histories of BMP image.A kind of blocking effect that is produced by JPEG (Joint Photographic Experts Group) compression that is based on is carried out the historical algorithm that detects of BMP image compression.If people such as Fan propose in " Identification of bitmap compression history:JPEGdetection and quantizer estimation " before the width of cloth BMP image not through the JPEG compression, then the margin of image element between the piece should be close, otherwise margin of image element then can be because of the blocking effect of JPEG compression difference, the compression histories that utilizes this Characteristics Detection to go out the BMP image also can utilize the maximum principle of similitude to estimate original quantum step afterwards.Although the method in the literary composition has obtained a reasonable testing result, but this method computational complexity is bigger, and along with the increase of compression quality factor, can not judge that the probability that whether compresses through JPEG before the BMP image becomes big, especially after the factor of quality is greater than 95, because the not obvious algorithm detection accuracy rate that causes of blocking effect sharply descends.Another kind of typical method is based on the detection method of Benford rule.2007, people such as Fu found that by a large amount of experiments first position effective digital of the JPEG coefficient of the jpeg image that single compresses meets broad sense Benford rule and distributes.The Benford rule is a formula commonly used in the economics.People such as Fu utilize this distribution character of the first significant digits of JPEG coefficient to classify by SVM (Support Vector Machine) grader in " A generalized Benford ' s law for JPEG coefficients and itsapplications in image forensics " literary composition can detect the BMP image before whether through the JPEG compression, and the rough estimate original compression factor of quality.In the literary composition experimental result show the method in the original compression factor of quality up to 99 o'clock, detect accuracy rate and still can reach 100%.But the application of Benford rule has a lot of restrictive conditions, as data the restriction of maximum and minimum value can not be set, and numerical value is change continuously in a very wide scope, and neither completely random is concentrated etc. only degree.Though therefore this kind method has reached very high accuracy rate in the experiment of document, but these restrictive conditions make the use of this method that certain limitation be arranged, as image such as the single image of tone such as large stretch of blue sky, greenery patches and do not meet this rule, picture size hour also can be influential.

Summary of the invention

The technical problem to be solved in the present invention provides a kind ofly carries out the method that the JPEG compression histories detects to single width or large quantities of BMP image.

Technical scheme of the present invention is as follows:

1.JPEG compression is to the influence of image JPEG coefficient

Image is called the JPEG coefficient through the DCT coefficient after piecemeal DCT (the Discrete Cosine Transform) transform and quantization, and it can directly read from jpeg image file.0 number is a principal element that influences the JPEG compression quality in the JPEG coefficient.Found through experiments, if be the jpeg image of different quality factor with same width of cloth BMP image compression, along with the increase of JPEG compression quality factor, picture quality constantly improves thereupon, and 0 percentage also can constantly reduce thereupon in 64 JPEG coefficients.

Therefore with 0 be defined as the information loss amount of image after at 64 locational number percentages of DCT through the JPEG compression, then the image information loss amount is big more, the jpeg image quality is poor more.If n (j) be in all DCT pieces on j JPEG coefficient positions 0 number and, m is the number of 8*8DCT piece, then the image information loss amount can be expressed as

$p\left(j\right)=\frac{n\left(j\right)}{m},j=\mathrm{1,2},...,64---\left(1\right)$

The average information loss amount is expressed as

$\mathrm{average}=\frac{{\mathrm{\Σ}}_1^{64}p\left(j\right)}{64}---\left(2\right)$

Shown among Fig. 1 and times got the result that a width of cloth BMP image calculates average information loss amount average after with the jpeg image of its boil down to factor of quality Q=75～100, as seen along with the increase of Q, average constantly reduces.

Therefore, with a BMP image I to be measured _BmpThe jpeg image I of boil down to Q=100 _Jpeg1, if I _BmpBe the JPEG compression of Q1 (Q1＜100) through the factor of quality, then the image information loss amount can directly be converted to the image information loss amount of the jpeg image of Q=100 greater than an original BMP image before.As long as by the image information loss amount of BMP image more to be measured and original BMP, just can judge BMP image to be measured before whether through the JPEG compression.Because JPEG compression is a lossy compression method, the original image before we can't return to the image through the JPEG compression before a width of cloth, so the applicant has adopted the method that testing image is sheared 4 row, 4 row to estimate original BMP image.

2. shear 4 row, 4 row and estimate original image

One width of cloth jpeg image is sheared the image that can regard as behind four lines four row after the calibration, as shown in Figure 2.Because after piece image sheared 4 row 4 row, the image information loss amount was little, if before the image through the JPEG compression, after it is sheared 4 row 4 row, can destroy the 8*8 partitioned organization of former JPEG compression, carry out then only having only last compression as seen after the JPEG compression once more.

With BMP image cut 4 row 4 row to be measured, then if compress through JPEG before the image, can destroy original pinch effect after shearing, can be similar to and regard the original original image that does not compress of a width of cloth as through JPEG; If do not compress before the image, even,, still can regard a width of cloth original image as because the image information loss amount is little then through the shearing manipulation of 4 row, 4 row through JPEG.

Therefore the present invention comes the approximate evaluation original image by testing image being sheared four lines four row, and is undertaken by the statistical nature that relatively extracts testing image with the information loss amount of testing image that the BMP image compression is historical to be detected.

3. the feature extraction of reflection image information loss amount

According to the JPEG compression influence to image JPEG coefficient, the JPEG coefficients statistics feature after the present invention has extracted BMP image to be measured and estimated the jpeg image of former figure boil down to Q=100 carries out that the BMP image compression is historical to be detected.

Is after the factor of quality is 90 jpeg image with a width of cloth by TIFF (the Tagged Image File Format) image compression of camera picked-up, again reading also again, decompress(ion) is condensed to a width of cloth BMP image, as shown in Figure 3, see the difference that to feel between it and the original tiff image from visual angle, but after 64 dimension p (j) features of extracting the two respectively, can find on the same DCT coefficient positions that 0 number percentage has very big difference, on 64 positions of former tiff image in the JPEG coefficient 0 ratio weight average much smaller than before through the BMP image of JPEG compression, as shown in Figure 4.

Therefore the present invention utilizes this phenomenon, supposes a given BMP image I to be measured _Bmp, to obtaining estimating former figure I behind its shearing four lines four row _Est, the jpeg image I that is Q=100 with this two width of cloth image compression respectively _Jpeg1And I _Jpeg2, the JPEG coefficient of the Y passage by reading this two width of cloth jpeg image respectively calculates p according to formula 1 _I1(j) and P _I2(j), j=1,2 ..., 64, i.e. image information loss amount on 64 DCT coefficient positions.Order

Z ₁＝NUM(p _I1(j)＞p _I2(j))，Z ₂＝NUM(p _I1(j)＜p _I2(j))

Wherein NUM () is for asking the number function.

Thereby obtain 2 dimensional feature Z ₁And Z ₂, as the few tolerance of image information loss amount increase and decrease.If BMP image I to be measured _BmpBefore not through JPEG compression, then image I _EstWith I _BmpThe image information loss amount should be similar to, show as Z ₁≈ Z ₂If I _BmpThrough JPEG compression, then because the JPEG compression is a lossy compression method, even decompress(ion) is condensed to the BMP image, still can lose some details, so be after 100 the jpeg image again with its boil down to factor of quality, the image information loss amount increases, and causes I before _EstIn some locational image information loss amount can increase, therefore, 2 dimensional features of being asked can show as Z ₁＞＞Z ₂

In sum, the present invention is as follows to the historical concrete steps that detect of BMP image compression:

Detect a width of cloth BMP image I _BmpBefore whether through the JPEG compression, at first it to be sheared and obtain a width of cloth behind 4 row, 4 row and estimate former figure I _Est, the jpeg image I that is Q=100 with this two width of cloth image compression respectively again _Jpeg1And I _Jpeg2Utilize in their the JPEG coefficient image information loss amount to carry out feature extraction, can utilize the Fisher linear classifier to carry out the compression histories of classification based training and test detection BMP image at last, also can utilize the proportionate relationship of extracting feature to carry out threshold value and cut apart, need not training and testing and just can judge single image.

Specific implementation step of the present invention as shown in Figure 5.

Effect benefit of the present invention is: digital picture is as judicial evidence, most importantly will judge that exactly whether it is through distorting.Before judging a width of cloth BMP image, whether compress, can make preliminary differentiation, supervise chain for the evidence of judicial department effective technical guarantee is provided the authenticity of image through JPEG.The present invention is applicable to information security field, can carry out the detection of compression histories to a given BMP image effectively.

Description of drawings

Fig. 1 is the variation diagram of image averaging information loss amount average with JPEG compression quality factor.

Among the figure: abscissa is the factor of quality of 75-100, and ordinate is the value of average.

Fig. 2 is that former figure method of estimation is promptly calibrated image acquisition methods figure.

Fig. 3 is the visual comparsion chart of the BMP image of original tiff image and the JPEG compression of passing through Q=90 originally.

Among the figure: (a) being original tiff image, (b) is the original BMP image that compresses through the JPEG of Q=90.

Fig. 4 is 0 a proportion map in the JPEG coefficient on 64 DCT positions.

Among the figure: the cross lines are 90 bmp image through 0 proportion in the JPEG coefficient after the compression of Q=100 for the original compression factor of quality, and the square lines are original tiff image.

Fig. 5 is the whole performing step schematic diagram of the inventive method.

Embodiment

Below in conjunction with technical scheme and accompanying drawing, be described in detail the specific embodiment of the present invention.

300 width of cloth tiff images of having selected in the experiment to be absorbed by Kodak DC290 camera comprise two kinds of resolution as original lossless image, are respectively 720*480 and 1440*960, and with the former figure difference of this 300 width of cloth TIFF boil down to Q={60,70,80,85,90,95,96,97,98, change into the BMP image behind the jpeg image of 99} again, as original BMP image through the JPEG compression.Because along with reducing of compression quality factor Q, image impairment information is many more, picture quality also can be poor more, theoretically, the detection effect of algorithm also can be good more, so, the present invention has selected 3 lower compression quality factor Q={60 commonly used, 70,80,85} is used for the validity of testing algorithm, has selected to be up to 6 higher compression quality factor Q={90 of 99,95,96,97,98,99}.Obtained 300*10=3000 width of cloth image so altogether.

Utilize the 2 dimension JPEG coefficient characteristics of extracting, consider that intrinsic dimensionality is few, use the fisher linear classifier in the experiment, 200 width of cloth are used for training in 300 width of cloth images, and 100 width of cloth are used for testing, and original tiff image was respectively Q={60 with original through the factor of quality, 70,80,85,90,95,96,97,98, the BMP image of the JPEG compression of 99} carries out man-to-man class test.Test result is as shown in table 1.

Table 1 the present invention is experimental result one to one

?Q＝	?60	??70	??80	??85	??90	??95	??96	??97	??98	??99
											Former figure (%)	?100	??100	??100	??100	??100	??100	??100	??100	??100	??99
Original through the BMP of overcompression image (%)	?100	??100	??100	??100	??100	??100	??100	??100	??100	??91
											Average accuracy rate (%)	?100	??100	??100	??100	??100	??100	??100	??100	??100	??95

Even method proposed by the invention at original compression factor of quality Q up to 98 o'clock, still can 100% accurately classification because during Q=99, JPEG compression losses information is less, detect comparatively difficulty, but accuracy rate has also reached 95%.In actual conditions, the factor of quality of original compression is unknown, therefore we have carried out mixed survey experiment to this method, be Q={60 promptly from the original compression factor of quality, 70,80,85,90,95,96,97,98, choose the different image of 20 width of cloth in the BMP image of 99} respectively and form 200 width of cloth training images, every kind of quality factor is chosen 10 width of cloth images composition test set respectively from 100 remaining width of cloth images again, former tiff image selects 200 width of cloth as training, and 100 width of cloth utilize the fisher linear classifier to classify as test, then original BMP image classification accuracy rate is 100%, and lower through the BMP of overcompression image classification accuracy rate before, be 92%, the consideration reason is that the image of Q=99 in the training and testing image is more, and the image proportion of compression quality factor Q=99 is very little before in the practical application, therefore removes Q=99 mixed survey model accuracy rate afterwards and has all reached 100%.

Select 5 width of cloth blue skies, the original image in greenery patches utilizes mixed survey model of the present invention to test, and 5 width of cloth images all accurately are judged as original image.

In addition, found through experiments original image and the characteristic Z of passing through the BMP image of JPEG compression before ₁With Z ₂Ratio have than big difference, therefore, can consider and need not train, whether judge before the image through the JPEG compression with threshold segmentation method.If $Z=\frac{Z_1}{Z_2},$ Table 2 has shown the result who 300 width of cloth images is calculated the Z value respectively.

The Z value result of calculation of table 2300 width of cloth image

??Z	Former figure	??Q＝60	??Q＝70	??Q＝80	??Q＝85	??Q＝90	??Q＝95	??Q＝96	?Q＝97	??Q＝98	??Q＝99
												Minimum value	??0.44	??10.20	??7.43	??3.54	??3.82	??6.43	??3.62	??4.78	??2.6	??1.47	??0.84
Maximum	??1.90	??Inf	??Inf	??Inf	??Inf	??Inf	??Inf	??Inf	??Inf	??Inf	??62

300 width of cloth original images have been listed in the table and before through the maximum and the minimum value of the Z value of the BMP image of different quality factor compression, wherein Inf represents infinity, and Z is described ₂=0.In image 300 width of cloth of Z during Q=99＜2.0 35 width of cloth are only arranged, in image 300 width of cloth of Z during Q=98＜2.0 2 width of cloth are only arranged, in image 300 width of cloth of Z among the former figure＞2.0 2 width of cloth are only arranged.Therefore, can with 2.0 as distinguish original image with originally through a threshold value of the BMP of overcompression image, a given width of cloth BMP image only needs to calculate its Z value, can judge tentatively just whether it originally compresses through JPEG.

Calculate original image and this 5 width of cloth original image boil down to Q={85 on blue sky, meadow respectively, 95, the jpeg image of 99} decompress(ion) again is condensed to behind the BMP image to such an extent that Z value result is as shown in table 3.

Table 35 width of cloth blue sky, greenery patches image Z value result

The Z value	Former figure	??Q＝85	??Q＝95	??Q＝99
					The 1st width of cloth	??0.97	??Inf	??Inf	??20.33
The 2nd width of cloth	??0.68	??Inf	??Inf	??4.17
					The 3rd width of cloth	??0.97	??Inf	??63	??7.00
The 4th width of cloth	??0.72	??Inf	??Inf	??4.18
					The 5th width of cloth	??1.27	??63	??61	??3.29

As seen the Z value of original image is all in threshold value below 2.0, even and before through the BMP image original compression factor of quality of JPEG compression up to 99 o'clock, still in threshold value more than 2.0, so the present invention stands good to the single tone images of sheet.

Claims (4)

1. one kind based on the historical detection method of the BMP image compression of image information loss amount, it is characterized in that only obtaining under the situation of digital picture, by original image is estimated in BMP image cut 4 row to be measured 4 row backs, and with testing image with estimate that the former figure boil down to factor of quality is 100 jpeg image, relatively the image information loss amount of this two width of cloth jpeg image is extracted feature, and Billy that then can be by this 2 dimensional feature is cut apart with threshold value single width BMP image compression history is differentiated or utilized the Fisher linear classifier that a large amount of BMP images are carried out classification and Detection.

2. the historical detection method of a kind of BMP image compression according to claim 1 based on the image information loss amount, the former figure that it is characterized in that calculating testing image and estimation weighs the image information loss amount through 0 proportion on 64 positions in the JPEG compression back JPEG coefficient of Q=100, obtains 2 dimensional features by both image information loss amount sizes relatively;

The S2-1.2 dimensional feature:

Z ₁＝NUM(p _I1(j)＞p _I2(j))，Z ₂＝NUM(p _I1(j)＜p _I2(j))

Wherein NUM () is for asking number function, p _I1(j) and p _I2(j), j=1,2 ..., 64, be respectively testing image and estimate the image information loss amount of former figure on 64 DCT coefficient positions;

S2-2. image information loss amount:

$p\left(j\right)=\frac{n\left(j\right)}{m},j=\mathrm{1,2},...,64$

Wherein n (j) be in all DCT pieces on j JPEG coefficient positions 0 number and, m is the number of 8*8DCT piece in the image.

3. the historical detection method of a kind of BMP image compression according to claim 1 based on the image information loss amount, it is characterized in that testing image is sheared 4 row, 4 column weights newly to save as the BMP image and be used for eliminating former JPEG pinch effect, obtains being similar to the former figure of estimation of former BMP image statistics feature.

4. the historical detection method of a kind of BMP image compression based on the image information loss amount according to claim 1 is characterized in that carrying out threshold value by the ratio that calculates 2 dimensional features cuts apart and can carry out the compression histories differentiation or use the Fisher linear classifier to carry out classification and Detection to several BMP images single width BMP image.

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