JP5235850B2 - Image encoding apparatus, image decoding apparatus, image encoding / decoding system and method thereof - Google Patents

Description

  The present invention, for example, encodes a watermarked image obtained by combining an original image and a watermark image to generate an encoded image, and decodes and restores the encoded image generated by the image encoding device. The present invention relates to an image encoding / decoding system including an image decoding apparatus that generates an image and a method thereof.

  In a conventional image encoding / decoding system, when compressing and encoding an input image, the designated area of the original image before compression is replaced with a dummy image and lossless compression encoding is performed. In addition, by re-substituting the designated area of the image obtained by decoding the dummy image, it is possible to obtain an original image that does not remain affected by the visible additional information (see, for example, Patent Document 1).

  The image encoding / decoding system disclosed in Patent Document 1 uses a method of embedding a pixel difference value between an original image and a dummy image before replacement as a digital watermark so that the original image can be restored. ing.

JP 2004-228876 A

  However, in the conventional image encoding / decoding system disclosed in Patent Document 1, since the pixel difference value between images is used as restoration data for the original image, the larger the dummy image, the larger the data of the restoration data. There was a problem of enormous size.

  In addition, since the target of the difference value of the dummy image is the original image before encoding, the image restored using the pixel difference value embedded as the digital watermark and the pixel value of the dummy image is of course encoded. The original image before conversion. On the other hand, the portion of the image area that is not the restoration target, that is, the original image area that has not been replaced with the dummy image is a deteriorated image after the encoding, and therefore when the entire restored image is viewed, it is replaced with the dummy image. There is a problem that the difference in image quality deterioration between the area that is not replaced and the area that is not replaced is noticeable, and that the subjective image quality deterioration may be perceived.

  The present invention has been made to solve the above-described problems, and is an image coding that can reduce the data size for restoration and can perform restoration without causing a difference in image quality degradation in the restored image. An object is to provide an apparatus, an image decoding apparatus, an image encoding / decoding system, and a method thereof.

  An image encoding apparatus according to the present invention combines an original image and a watermark image to generate a watermarked image, and first converts a watermarked image generated by the image combining unit by frequency conversion and quantization. Among the data calculated by the frequency conversion / quantization unit, the second frequency conversion / quantization unit that frequency-converts and quantizes the original image, and the second frequency conversion / quantization unit. A difference extraction unit that extracts data of a portion different from the data calculated by the frequency conversion / quantization unit, a first compression encoding unit that compresses and encodes data by the first frequency conversion / quantization unit, and a difference And a second compression encoding unit that compresses and encodes the data extracted by the extraction unit.

  According to the present invention, since it is configured as described above, only the data of the difference between the original image and the watermarked image is extracted and compression-encoded to generate restoration data. It is possible to reduce the data size and to perform restoration without causing a difference in image quality degradation in the restored image.

It is a block diagram which shows the image coding apparatus which concerns on Embodiment 1 of this invention. It is a flowchart which shows the encoding process by the image coding apparatus which concerns on Embodiment 1 of this invention. It is a figure which shows an example of the image composition by the image composition part in Embodiment 1 of this invention. It is a figure which shows the other example of the image composition by the image composition part in Embodiment 1 of this invention. It is a figure which shows the further another example of the image composition by the image composition part in Embodiment 1 of this invention. It is a figure explaining MCU in Embodiment 1 of this invention. It is a figure explaining the difference part extraction method by the difference extraction part in Embodiment 1 of this invention. It is a block diagram which shows another example of the image coding apparatus which concerns on Embodiment 1 of this invention. It is a block diagram which shows the image decoding apparatus which concerns on Embodiment 2 of this invention. It is a flowchart which shows the decoding process by the image decoding apparatus which concerns on Embodiment 2 of this invention. It is a block diagram which shows the image coding apparatus which concerns on Embodiment 3 of this invention. It is a flowchart which shows the encoding process by the image coding apparatus which concerns on Embodiment 3 of this invention. It is a figure explaining the difference part extraction method by the difference extraction part in Embodiment 3 of this invention. It is a block diagram which shows the image decoding apparatus which concerns on Embodiment 3 of this invention. It is a flowchart which shows the decoding process by the image decoding apparatus which concerns on Embodiment 3 of this invention. It is a block diagram which shows the image coding apparatus which concerns on Embodiment 4 of this invention. It is a flowchart which shows the encoding process by the image coding apparatus which concerns on Embodiment 4 of this invention. It is a block diagram which shows the image decoding apparatus which concerns on Embodiment 4 of this invention. It is a flowchart which shows the decoding process by the image decoding apparatus which concerns on Embodiment 4 of this invention. It is a block diagram which shows the image coding apparatus which concerns on Embodiment 5 of this invention. It is a block diagram which shows the image decoding apparatus which concerns on Embodiment 5 of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing an image encoding device 10 of an image encoding / decoding system according to Embodiment 1 of the present invention. Hereinafter, a case where a JPEG image is used as a target of an encoded image generated by the image encoding device 10 will be described.
As shown in FIG. 1, the image encoding device 10 includes an image synthesis unit 11, DCT (Discrete Cosine Transformation) conversion / quantization units 12a and 12b, a difference extraction unit 13a, and entropy encoding units 14a and 14b. .

  The image composition unit 11 inputs an original image and a visible watermark image to be inserted into the original image as a visible watermark, and synthesizes the original image data by superimposing the visible watermark image on the original image to generate a watermarked image. To do. The watermarked image generated by the image synthesizing unit 11 is transmitted to the DCT transform / quantization unit 12a.

  The DCT transform / quantization unit (first frequency transform / quantization unit) 12a performs DCT transform (frequency transform) on the watermarked image transmitted from the image composition unit 11, and further quantizes the quantized DCT coefficient. Is calculated. The quantized DCT coefficient data indicating the quantized DCT coefficient of the watermarked image calculated by the DCT transform / quantization unit 12a is transmitted to the difference extraction unit 13a and the entropy encoding unit 14a.

  The DCT transform / quantization unit (second frequency transform / quantization unit) 12b performs DCT transform on the input original image, further quantizes it, and calculates quantized DCT coefficients. The quantized DCT coefficient data indicating the quantized DCT coefficient of the original image calculated by the DCT transform / quantization unit 12b is transmitted to the difference extraction unit 13a.

  The difference extraction unit 13a is based on the quantized DCT coefficient data of the watermarked image transmitted from the DCT transform / quantization unit 12a and the quantized DCT coefficient data of the original image transmitted from the DCT transform / quantization unit 12b. Both quantized DCT coefficients are compared, and the quantized DCT coefficient of the original image corresponding to the difference is extracted. The quantized DCT coefficient data indicating the quantized DCT coefficient extracted by the difference extracting unit 13a is transmitted to the entropy encoding unit 14b.

  The entropy encoding unit (first compression encoding unit) 14a performs entropy encoding (compression) using a Huffman code based on the quantized DCT coefficient data of the watermarked image transmitted from the DCT transform / quantization unit 12a. Encoding) to calculate encoded image data.

  The entropy encoding unit (second compression encoding unit) 14b performs entropy encoding using a Huffman code based on the quantized DCT coefficient data of the original image of the difference portion transmitted from the difference extraction unit 13a. This is to calculate converted image data (extended data).

Next, the operation of the image encoding device 10 configured as described above will be described. FIG. 2 is a flowchart showing an encoding process performed by the image encoding device 10 according to Embodiment 1 of the present invention.
In the encoding process by the image encoding device 10, as shown in FIG. 2, first, the image synthesis unit 11 generates a watermarked image (step ST21). That is, the image synthesis unit 11 generates a watermarked image by superimposing a visible watermark image on the input original image and synthesizing the image.

3 to 5 are diagrams showing examples of image composition by the image composition unit 11 according to Embodiment 1 of the present invention. Here, the original image is an uncompressed bitmap image, and the visible watermark image is an uncompressed bitmap image having the same size as the original image. In this visible watermark image, the pixel value is not 0 only in the area including the logo to be inserted (gray area shown in FIGS. 3 to 5), and the pixel value is 0 in the other areas.
As shown in FIG. 3, the image composition unit 11 adds a pixel value at a corresponding position in the visible watermark image to each pixel value in the original image, thereby generating a watermarked image. For example, when the pixel value at a certain position of the original image is P and the pixel value at the position corresponding to the pixel value P of the original image of the visible watermark image is Q, it corresponds to the pixel value P of the original image of the watermarked image. The pixel value at the position is P + Q.

  Alternatively, as shown in FIG. 4, a constant value α satisfying 0 <α <1 is used, and α × P + (1−α) × Q is set as a pixel value at a position corresponding to the original image of the watermarked image. Thus, a transparent watermarked image can be generated.

Further, the visible watermark image is not necessarily the same size as the original image. For example, as shown in FIG. 5, the visible watermark image is set to the image size of only the region where the logo is inserted, and the insertion position coordinates (for example, A watermarked image may be generated by a method of separately designating the upper left coordinate of the logo area) to the image composition unit 11.
The watermarked image generated by the image synthesizing unit 11 is transmitted to the DCT transform / quantization unit 12a.

  Next, the DCT transform / quantization unit 12a calculates a quantized DCT coefficient of the watermarked image (step ST22). That is, the DCT transform / quantization unit 12a calculates a quantized DCT coefficient by DCT transforming the watermarked image transmitted from the image composition unit 11 and further performing quantization. Specifically, in the first embodiment, since the format of the encoded image is JPEG, the DCT transform / quantization unit 12a divides the watermarked image into blocks of 8 pixels horizontal by 8 pixels vertical. Thus, DCT transformation is performed for each block, and a quantized DCT coefficient obtained by quantizing the DCT coefficient according to a predetermined quantization table is calculated. The quantized DCT coefficient data indicating the quantized DCT coefficient of the watermarked image calculated by the DCT transform / quantization unit 12a is transmitted to the difference extraction unit 13a and the entropy encoding unit 14a.

  On the other hand, the DCT transform / quantization unit 12b calculates a quantized DCT coefficient of the original image (step ST23). That is, the DCT transform / quantization unit 12b performs a DCT transform on the input original image and further performs quantization to calculate a quantized DCT coefficient. Specifically, the DCT transform / quantization unit 12b divides the original image into blocks of 8 pixels in the horizontal direction and 8 pixels in the vertical direction, performs DCT conversion for each block, and calculates the DCT coefficient according to a predetermined quantization table. Quantized quantized DCT coefficients are calculated. The quantized DCT coefficient data indicating the quantized DCT coefficient of the original image calculated by the DCT transform / quantization unit 12b is transmitted to the difference extraction unit 13a.

  Next, the difference extraction unit 13a extracts a difference portion (step ST24). That is, the difference extraction unit 13a includes the quantized DCT coefficient data of the watermarked image transmitted from the DCT transform / quantization unit 12a, and the quantized DCT coefficient data of the original image transmitted from the DCT transform / quantization unit 12b. And the quantized DCT coefficients of the original image corresponding to the difference are extracted.

  Here, in the case of the JPEG format, the quantized DCT coefficients are grouped in a unit called MCU (Minimum Coded Unit). As shown in FIG. 6, this MCU has a luminance Y component and two color difference Cb and Cr components in a block unit of 16 horizontal pixels × 16 vertical pixels, which is a collection of 4 neighboring blocks of 8 horizontal pixels × 8 vertical pixels. This is a data unit in which the quantized DCT coefficients are summarized.

As the difference extraction method using the MCU by the difference extraction unit 13a, for example, as shown in FIG. 7, the quantization DCT coefficient of the watermarked image and the quantization DCT coefficient of the original image are compared for each MCU. There is a method of collecting and extracting only MCUs of original images having different quantized DCT coefficients. Although not shown, the difference extraction unit 13a attaches MCU position information indicating which part of the MCU is extracted as additional information to the extracted quantized DCT coefficient data.
The quantized DCT coefficient data indicating the quantized DCT coefficient of the original image of the difference portion extracted by the difference extraction unit 13a is transmitted to the entropy encoding unit 14b.

  Next, the entropy encoding unit 14a generates an encoded image (step ST25). That is, the entropy encoding unit 14a performs entropy encoding using a Huffman code on the quantized DCT coefficient data of the watermarked image transmitted from the DCT transform / quantization unit 12a, thereby converting the watermarked image. An encoded image compressed as a JPEG image is generated. In the image encoding device 10, the description of the process for the part that generates the JPEG header is omitted.

  On the other hand, the entropy encoding unit 14b generates extension data (step ST26). That is, the entropy encoding unit 14b generates extension data by performing entropy encoding using a Huffman code on the quantized DCT coefficient data of the original image of the difference portion transmitted from the difference extraction unit 13a. This extended data is data necessary for generating a restored image corresponding to the original image.

  Step ST21 corresponds to the image composition step of the present invention, step ST22 corresponds to the first DCT transform / quantization step of the present invention, and step ST23 corresponds to the second DCT transform / quantization step of the present invention. Correspondingly, step ST24 corresponds to the difference extraction step of the present invention, step ST25 corresponds to the first compression encoding step of the present invention, and step ST26 corresponds to the second compression encoding step of the present invention.

  Further, as shown in FIG. 8, the encoded image generated by the entropy encoding unit 14a and the extension data generated by the entropy encoding unit 14b are added to the configuration of the image encoding device 10 shown in FIG. You may provide the image output part 15 which produces | generates the JPEG image file put together in one. In this case, for example, a method of storing extension data in an APPn segment (application data) in JPEG format is conceivable.

  As described above, according to the first embodiment of the present invention, the watermarked image generated by synthesizing the original image and the visible watermark image is subjected to DCT transformation / quantization and entropy-coded for encoding. Since the encoded image is generated, the quantized DCT coefficient of the original image corresponding to the difference from the quantized DCT coefficient of the watermarked image is entropy-encoded, so that the restoration corresponding to the original image is performed from the encoded image. Extended data necessary for generating an image can be generated (a method of restoration will be described in the next embodiment). At this time, since only the quantized DCT coefficients of the original image corresponding to the difference from the watermarked image are extracted and entropy-encoded, the data size of the extended data can be reduced.

  In the image encoding device 10 according to the first embodiment, JPEG compression is taken as an example, but each process by the image encoding device 10 is not necessarily limited to this description. For example, the image synthesizing unit 11 is not limited to simple addition or transparent addition of each pixel value as an image synthesizing method, and the DCT transform / quantization units 12a and 12b only perform DCT transform as a frequency transform method. The difference extraction unit 13a is not limited to data comparison in MCU units, and the entropy encoding units 14a and 14b are entropy encoding using a Huffman code as a compression encoding method. It is not limited to only.

Embodiment 2. FIG.
In the first embodiment, an encoded image obtained by entropy-encoding a watermarked image and an image encoding device 10 that generates extension data for restoring the original image from the encoded image have been described. An image decoding device 20 that generates a restored image corresponding to the original image using the encoded image and the extended data will be described.
FIG. 9 is a block diagram showing an image decoding apparatus 20 of the image encoding / decoding system according to Embodiment 2 of the present invention.
As shown in FIG. 9, the image decoding device 20 includes entropy decoding units 21 a and 21 b, a difference restoration unit 22 a, and an inverse quantization / DCT inverse conversion unit 23.

  The entropy decoding unit (first compression decoding unit) 21a performs entropy decoding (compression decoding) using a Huffman code on the input encoded image. The quantized DCT coefficient data indicating the quantized DCT coefficient of the watermarked image generated by the entropy decoding unit 21a is transmitted to the difference restoring unit 22a.

  The entropy decoding unit (second compression decoding unit) 21b performs entropy decoding using a Huffman code on the input extension data. The quantized DCT coefficient data indicating the quantized DCT coefficient of the original image of the difference part generated by the entropy decoding unit 21b is transmitted to the difference restoration unit 22a.

  The difference restoration unit 22a is based on the quantized DCT coefficient data of the watermarked image transmitted from the entropy decoding unit 21a and the quantized DCT coefficient data of the original image of the difference part transmitted from the entropy decoding unit 21b. The quantized DCT coefficient of the original image is generated. The quantized DCT coefficient data indicating the quantized DCT coefficient of the original image generated by the difference restoration unit 22 a is transmitted to the inverse quantization / DCT inverse transform unit 23.

  The inverse quantization / DCT inverse transform unit (inverse quantization / frequency inverse transform unit) 23 performs inverse quantization on the quantized DCT coefficient data of the original image transmitted from the difference restoration unit 22a, and then performs DCT inverse transform. By performing (frequency inverse transform), a decoded image corresponding to the original image is generated.

Next, the operation of the image decoding apparatus 20 configured as described above will be described. FIG. 10 is a flowchart showing decoding processing by the image decoding apparatus 20 according to Embodiment 2 of the present invention.
In the decoding process by the image decoding apparatus 20, as shown in FIG. 10, first, the entropy decoding unit 21a decodes the encoded image (step ST101). That is, the entropy decoding unit 21a generates quantized DCT coefficients of a watermarked image by performing entropy decoding using a Huffman code on the input encoded image. The quantized DCT coefficient data indicating the quantized DCT coefficient generated by the entropy decoding unit 21a is transmitted to the difference restoring unit 22a.

  On the other hand, the entropy decoding unit 21b decodes the extension data (step ST102). That is, the entropy decoding unit 21b performs the entropy decoding using the Huffman code on the input extension data, thereby generating the quantized DCT coefficient of the original image of the difference portion. The quantized DCT coefficient data indicating the quantized DCT coefficient generated by the entropy decoding unit 21b is transmitted to the difference restoration unit 22a.

  Next, the difference restoration unit 22a restores the quantized DCT coefficient of the original image (step ST103). That is, the difference restoration unit 22a is based on the quantized DCT coefficient data of the watermarked image transmitted from the entropy decoding unit 21a and the quantized DCT coefficient data of the original image of the difference part transmitted from the entropy decoding unit 21b. Thus, quantized DCT coefficients of the original image are generated. Specifically, the difference restoration unit 22a, based on the position information of the MCU attached to the extension data, for the quantized DCT coefficient of the watermarked image that is the difference portion and the quantized DCT coefficient of the original image, Replace the quantized DCT coefficient of the original image of the corresponding difference part. The quantized DCT coefficient data indicating the quantized DCT coefficient of the original image generated by the difference restoration unit 22 a is transmitted to the inverse quantization / DCT inverse transform unit 23.

  Next, the inverse quantization / DCT inverse transform unit 23 generates a decoded image (step ST104). That is, the inverse quantization / DCT inverse transform unit 23 performs inverse quantization on the quantized DCT coefficient data of the original image transmitted from the difference restoration unit 22a, returns the DCT coefficient, and then performs DCT inverse transform. Thus, a decoded image corresponding to the original image is generated. In addition, since the target JPEG in the image decoding apparatus 20 according to the second embodiment assumes lossy compression, the decoded image is not necessarily exactly the same as the original image.

  Step ST101 corresponds to the first compression decoding step of the present invention, step ST102 corresponds to the second compression decoding step of the present invention, step ST103 corresponds to the difference restoration step of the present invention, step ST102 ST104 corresponds to the inverse quantization / DCT inverse transform step of the present invention.

  As described above, according to the second embodiment of the present invention, the encoded image and the extension data are entropy-decoded, and the quantized DCT coefficient at the corresponding position of the quantized DCT coefficient data of the watermark image is changed to the original image of the difference portion. Therefore, it is possible to decode the original image before insertion of the visible watermark image, more precisely image data obtained by JPEG compression of the original image. Further, unlike the conventional image decoding apparatus, a phenomenon in which the degree of image quality deterioration differs between the area corresponding to the visible watermark image and the other area does not occur, and the subjective image quality due to the difference in deterioration does not occur. There is no longer any sense of deterioration.

Embodiment 3 FIG.
In the first embodiment, extended data is generated by extracting the quantized DCT coefficient of the original image which is a difference from the quantized DCT coefficient of the watermarked image in the image coding apparatus 10. In the third form, extension data is generated using a difference value between the quantized DCT coefficient of the watermarked image and the quantized DCT coefficient of the original image.
FIG. 11 is a block diagram showing an image encoding device 10 of an image encoding / decoding system according to Embodiment 3 of the present invention. The image coding apparatus 10 according to Embodiment 3 shown in FIG. 11 changes the difference extraction unit 13a of the configuration of the image coding apparatus 10 according to Embodiment 1 shown in FIG. The converting unit 14b is changed to the entropy encoding unit 14c, the other configurations are the same, and the same reference numerals are given, and the description thereof is omitted.

  The difference extraction unit 13b is based on the quantized DCT coefficient data of the watermarked image transmitted from the DCT transform / quantization unit 12a and the quantized DCT coefficient data of the original image transmitted from the DCT transform / quantization unit 12b. Both quantized DCT coefficients are compared, and a difference value is calculated and extracted. Difference value data indicating the difference value calculated by the difference extraction unit 13b is transmitted to the entropy encoding unit 14c.

  The entropy encoding unit (third compression encoding unit) 14c calculates extension data by performing entropy encoding using a Huffman code based on the difference value data transmitted from the difference extraction unit 13b.

Next, the operation of the image coding apparatus 10 configured as described above will be described. FIG. 12 is a flowchart showing an encoding process performed by the image encoding device 10 according to the third embodiment.
In the encoding process by the image encoding device 10 according to the third embodiment shown in FIG. 12, the same processing as the encoding process by the image encoding device 10 according to the first embodiment shown in FIG. To simplify the description.

  In the encoding process by the image encoding device 10, as shown in FIG. 12, first, the image composition unit 11 generates a watermarked image (step ST21). Next, the DCT transform / quantization unit 12a calculates the quantized DCT coefficient of the watermarked image, and the DCT transform / quantization unit 12b calculates the quantized DCT coefficient of the original image (steps ST22 and ST23).

Next, the difference extraction unit 13b calculates difference value data (step ST121). That is, the difference extraction unit 13b includes the quantized DCT coefficient data of the watermarked image transmitted from the DCT transform / quantization unit 12a and the quantized DCT coefficient data of the original image transmitted from the DCT transform / quantization unit 12b. As shown in FIG. 13, a difference value obtained by subtracting the byte value of the quantized DCT coefficient of the watermarked image from the byte value of the quantized DCT coefficient of the original image is calculated for each MCU. Then, MCUs whose difference values are all 0 (the MCUs having no difference) are ignored, and only MCUs including the difference values that are not 0 are extracted. Although not shown, the difference extraction unit 13b attaches the position information of the MCU indicating which part of the MCU is extracted as additional information to the extracted quantized DCT coefficient data.
Difference value data indicating the difference value calculated by the difference extraction unit 13b is transmitted to the entropy encoding unit 14c.

Next, the entropy encoding unit 14a generates an encoded image (step ST25).
On the other hand, the entropy encoding unit 14c generates extension data (step ST122). That is, the entropy encoding unit 14c generates extension data by performing entropy encoding using a Huffman code on the difference value data transmitted from the difference extraction unit 13b. This extended data is data necessary for generating a restored image corresponding to the original image.

Next, the image decoding device 20 that generates a decoded image corresponding to the original image using the encoded image and the extended data encoded by the image encoding device 10 will be described.
FIG. 14 is a block diagram showing an image decoding apparatus 20 of an image encoding / decoding system according to Embodiment 3 of the present invention. The image decoding device 20 according to Embodiment 3 shown in FIG. 14 is obtained by changing the difference restoration unit 22a of the configuration of the image decoding device 20 according to Embodiment 2 shown in FIG. 9 to a difference restoration unit 22b. Other configurations are the same, and the same reference numerals are given, and the description thereof is omitted.

  The entropy decoding unit 21b performs entropy decoding using the Huffman code on the received extension data to generate difference value data. The difference value data generated by the entropy decoding unit 21b is transmitted to the difference restoring unit 22b.

  Based on the quantized DCT coefficient data of the watermarked image transmitted from the entropy decoding unit 21a and the difference value data transmitted from the entropy decoding unit 21b, the difference restoration unit 22b performs the quantization DCT coefficient of the original image. Is generated. The quantized DCT coefficient data indicating the quantized DCT coefficient of the original image generated by the difference restoring unit 22b is transmitted to the inverse quantization / DCT inverse transform unit 23.

  Next, the operation of the image decoding apparatus 20 configured as described above will be described. FIG. 15 is a flowchart showing a decoding process by the image decoding apparatus 20 according to the third embodiment. In the decoding process by the image decoding apparatus 20 according to Embodiment 3 shown in FIG. 15, the same reference numerals are used for the same processes as the decoding process by the image decoding apparatus 20 according to Embodiment 2 shown in FIG. To simplify the description.

In the decoding process by the image decoding apparatus 20, as shown in FIG. 15, first, the entropy decoding unit 21a decodes the encoded image (step ST101).
On the other hand, the entropy decoding unit 21b decodes the extension data (step ST151). That is, the entropy decoding unit 21b generates difference value data by performing entropy decoding using a Huffman code on the received extension data. The difference value data generated by the entropy decoding unit 21b is transmitted to the difference restoring unit 22b.

Next, the difference restoration unit 22b restores the quantized DCT coefficient of the original image (step ST152). That is, the difference restoration unit 22b performs quantization DCT of the original image based on the quantized DCT coefficient data of the watermarked image transmitted from the entropy decoding unit 21a and the difference value data transmitted from the entropy decoding unit 21b. Generate coefficients. Specifically, based on the position information of the MCU attached to the extension data, the difference restoration unit 22b applies the difference between the quantized DCT coefficient of the original image and the quantized DCT coefficient of the watermarked image that is the difference portion. Add the corresponding difference values. The quantized DCT coefficient data indicating the quantized DCT coefficient of the original image generated by the difference restoring unit 22b is transmitted to the inverse quantization / DCT inverse transform unit 23.
Next, the inverse quantization / DCT inverse transform unit 23 generates a decoded image (step ST104).

  Step ST121 corresponds to the difference extraction step of the present invention, step ST122 corresponds to the third compression encoding step of the present invention, and step ST152 corresponds to the difference restoration step of the present invention.

  As described above, according to the third embodiment of the present invention, a watermarked image is DCT transformed, quantized, and entropy-coded to generate an encoded image, while a difference portion watermarked image quantized DCT Since the difference value between the coefficient and the quantized DCT coefficient of the original image is configured to be entropy-encoded, it is possible to generate extension data necessary for restoring the original image.

At this time, since only the difference value between the quantized DCT coefficient of the watermarked image of the difference portion and the quantized DCT coefficient of the original image is extracted and entropy-encoded, the data size of the extended data is reduced. Can do.
This method is particularly effective when superimposing by transparent addition as shown in FIG. 3 is performed in the image composition in the image composition unit 11. In the case of transparent addition, since the influence of the original image remains in the watermarked image after synthesis, the values of the quantized DCT coefficients of the original image and the watermarked image match or are relatively close to each other. It is expected that many parts will be generated. Therefore, there is a high possibility that the difference value data will often generate 0 or a value close to 0. In such a case, if entropy encoding is performed, the compression effect is highly likely to be obtained. The effect is increased.

  In the image encoding device 10 according to the third embodiment, the case where JPEG compression is taken as an example is shown, but each process by the image encoding device 10 is not necessarily limited to this description. This is the same as in the first embodiment.

Embodiment 4 FIG.
In the first embodiment, the difference extraction unit extracts the difference portion of the quantized DCT coefficient to generate the extended data. In the third embodiment, the difference extraction unit calculates the difference value of the quantized DCT coefficient. Although the extended data is generated, the fourth embodiment selects processing by the difference extraction unit and processing by the difference extraction unit based on the data amount.
FIG. 16 is a block diagram showing an image encoding device 10 of an image encoding / decoding system according to Embodiment 4 of the present invention. An image encoding device 10 according to Embodiment 4 shown in FIG. 16 has a difference extraction unit 13b, an entropy encoding unit 14c, and a data selection unit 16 in addition to the configuration of the image encoding device 10 according to Embodiment 1 shown in FIG. The other components are the same, and are given the same reference numerals and explanations thereof are omitted.

  The data selection unit 16 compares the extension data based on the quantized DCT coefficient data of the difference portion transmitted from the entropy encoding unit 14b and the extension data based on the difference value data transmitted from the entropy encoding unit 14c, The smaller data amount is selected and output.

Next, the encoding process by the image encoding device 10 configured as described above will be described.
FIG. 17 is a flowchart showing an encoding process by the image encoding apparatus 10 according to the fourth embodiment. In the encoding process by the image encoding device 10 according to the fourth embodiment shown in FIG. 17, the encoding process by the image encoding device 10 according to the first embodiment shown in FIG. 2 and the third embodiment shown in FIG. The same processes as those of the encoding process by the image encoding apparatus 10 according to the above are denoted by the same reference numerals, and the description will be simplified.

In the encoding process by the image encoding device 10, as shown in FIG. 17, first, the image composition unit 11 generates a watermarked image (step ST21). Next, the DCT transform / quantization unit 12a calculates the quantized DCT coefficient of the watermarked image, and the DCT transform / quantization unit 12b calculates the quantized DCT coefficient of the original image (steps ST22 and ST23). The quantized DCT coefficient data indicating the quantized DCT coefficients calculated by the DCT transform / quantization units 12a and 12b is transmitted to the difference extraction unit 13a and the difference extraction unit 13b.
Next, the difference extraction unit 13a extracts a difference portion (step ST24). On the other hand, the difference extraction unit 13b calculates difference value data (step ST121). Steps ST24 and ST121 are processed in parallel.

Next, the entropy encoding unit 14a generates an encoded image (step ST25).
On the other hand, the entropy encoding unit 14b entropy-encodes the quantized DCT coefficient data of the original image of the difference portion transmitted from the difference extraction unit 13a to generate extended data (step ST26). The extension data generated by the entropy encoding unit 14b is transmitted to the data selection unit 16.
On the other hand, the entropy encoding unit 14c entropy-encodes the difference value data transmitted from the difference extraction unit 13b to generate extended data (step ST122). The extension data generated by the entropy encoding unit 14 c is transmitted to the data selection unit 16.
Steps ST26 and ST122 are processed in parallel.

Next, the data selection unit 16 selects extension data (step ST171). In other words, the data selection unit 16 receives the extension data processed in parallel by the entropy encoding unit 14b and the entropy encoding unit 14c, compares the data amounts of both extension data in MCU units, and more data Select and output extended data with a small amount.
Although not shown, the data selection unit 16 selects selection information indicating whether the selected extension data is quantized DCT coefficient data or difference value data of the original image of the difference portion. Attached as additional information.

Next, the image decoding device 20 that generates a decoded image corresponding to the original image using the encoded image and the extended data encoded by the image encoding device 10 will be described.
FIG. 18 is a block diagram showing an image decoding apparatus 20 of an image encoding / decoding system according to Embodiment 4 of the present invention. The image decoding apparatus 20 according to Embodiment 4 shown in FIG. 18 is obtained by adding a difference restoration unit 22b and a data determination unit 24 to the configuration of the image decoding apparatus 20 according to Embodiment 1 shown in FIG. In other respects, the configuration is the same, and the same reference numerals are given and the description thereof is omitted.

  The entropy decoding unit 21b performs entropy decoding using a Huffman code on the received extension data to generate quantized DCT coefficient data or difference value data. The data generated by the entropy decoding unit 21b is transmitted to the data determination unit 24.

  Based on the selection information included in the additional information added to the extension data, the data determination unit 24 uses the data transmitted from the entropy decoding unit 21b to quantize DCT coefficient data or difference value data of the original image of the difference portion. It is determined whether it is. When the data determination unit 24 determines that the data transmitted from the entropy decoding unit 21b is the quantized DCT coefficient data of the original image of the difference portion, the data determination unit 24 transmits this data to the difference restoration unit 22a. On the other hand, when the data determination unit 24 determines that the data transmitted from the entropy decoding unit 21b is difference value data, the data determination unit 24 transmits this data to the difference restoration unit 22b.

  Next, the operation of the image decoding apparatus 20 configured as described above will be described. FIG. 19 is a flowchart showing a decoding process performed by the image decoding apparatus 20 according to the fourth embodiment. In the decoding process by the image decoding apparatus 20 according to the fourth embodiment shown in FIG. 19, the decoding process by the image decoding apparatus 20 according to the second embodiment shown in FIG. 10 and the third embodiment shown in FIG. The same processes as the decoding process performed by the image decoding apparatus 20 according to the above are denoted by the same reference numerals, and the description will be simplified.

  In the decoding process by the image decoding apparatus 20, as shown in FIG. 19, first, the entropy decoding unit 21a decodes the encoded image (step ST101). On the other hand, the entropy decoding unit 21b decodes the extension data (step ST191). That is, the entropy decoding unit 21b performs the entropy decoding using the Huffman code on the received extension data, thereby generating quantized DCT coefficient data or difference value data of the original image of the difference portion. The data generated by the entropy decoding unit 21b is transmitted to the data determination unit 24.

  Next, the data determination unit 24 determines whether the received data is quantized DCT coefficient data (step ST192). In other words, the data determination unit 24 is the quantized DCT coefficient data of the original image of the difference portion based on the selection information included in the additional information added to the extension data, and the data transmitted from the entropy decoding unit 21b. It is determined whether or not.

In step ST192, when it is determined that the data received by the data determination unit 24 is quantized DCT coefficient data of the original image of the difference portion, this data is transmitted to the difference recovery unit 22a, and then the difference recovery unit 22a restores the quantized DCT coefficient of the original image (step ST103).
On the other hand, if the data received by the data determination unit 24 is determined to be difference value data in step ST192, this data is transmitted to the difference restoration unit 22b, and the difference restoration unit 22b then quantizes the original image. The DCT coefficient is restored (step ST152).
Next, the inverse quantization / DCT inverse transform unit 23 generates a decoded image (step ST104).

  Step ST171 corresponds to the data selection step of the present invention, and step ST192 corresponds to the data determination step of the present invention.

  As described above, according to the fourth embodiment, when encoding is performed in the image encoding device 10, data having a small data amount among the quantized DCT coefficient data and the difference value data of the original image of the difference portion. Is selected as the extension data, in addition to the effects of the first to third embodiments, further data reduction of the extension data can be performed.

Embodiment 5 FIG.
The first embodiment generates extended data by extracting the quantized DCT coefficient of the difference between the original image, the watermarked image, and the original image, but the fifth embodiment encrypts this data. To do.
FIG. 20 is a block diagram showing an image encoding device 10 of an image encoding / decoding system according to Embodiment 5 of the present invention. In the image coding device 10 according to the fifth embodiment shown in FIG. 20, the extension data transmitted from the entropy coding unit 14b is encrypted in the configuration of the image coding device 10 according to the first embodiment shown in FIG. The data encryption unit 17 is added.

  FIG. 21 is a block diagram showing an image decoding apparatus 20 of the image encoding / decoding system according to Embodiment 5 of the present invention. In the image decryption apparatus 20 according to the fifth embodiment shown in FIG. 21, when the input extension data is encrypted in the configuration of the image decryption apparatus 20 according to the second embodiment shown in FIG. An encryption / decryption unit 25 for canceling the encryption is added.

  Note that the data encryption unit 17 of the image encoding device 10 according to the fifth embodiment and the encryption / decryption unit 25 of the image decoding device 20 are the same as those of the image encoding device 10 and the second embodiment of the first embodiment. The present invention can be similarly applied not only to the image decoding device 20 according to the present invention but also to the image coding device 10 and the image decoding device 20 according to the third and fourth embodiments.

  As described above, according to the fifth embodiment of the present invention, since the extended data is configured to be encrypted, it is possible to limit the restoration of the original image using the watermarked image. That is, for example, only a limited user having a key necessary for decryption can restore the original image, and other users can be prohibited from restoring the original image.

  DESCRIPTION OF SYMBOLS 10 Image coding apparatus, 11 Image composition part, 12a DCT transformation / quantization part (first frequency transformation / quantization part), 12b DCT transformation / quantization part (second frequency transformation / quantization part), 13a Difference extraction unit, 13b Difference extraction unit, 14a Entropy encoding unit (first compression encoding unit), 14b Entropy encoding unit (second compression encoding unit), 14c Entropy encoding unit (third compression code) Conversion unit), 15 image output unit, 16 data selection unit, 17 data encryption unit, 20 image decryption device, 21a entropy decryption unit (first compression decryption unit) 21b entropy decryption unit (second compression) Decryption unit), 22a difference restoration unit, 22b difference restoration unit, 23 inverse quantization / DCT inverse transform unit (inverse quantization / frequency inverse transform unit), 24 data determination unit, 25 encryption decryption unit

Claims (17)

An image composition unit that synthesizes the original image and the watermark image to generate a watermarked image;
A first frequency conversion / quantization unit for frequency-converting and quantizing the watermarked image generated by the image synthesis unit;
A second frequency conversion / quantization unit for frequency-converting and quantizing the original image;
Of the data calculated by the second frequency conversion / quantization unit, a difference extraction unit that extracts data of a portion different from the data calculated by the first frequency conversion / quantization unit;
A first compression encoding unit for compressing and encoding data by the first frequency transform / quantization unit;
An image encoding apparatus comprising: a second compression encoding unit that compresses and encodes the data extracted by the difference extraction unit. An image composition unit that synthesizes an original image and a watermark image to generate a watermarked image;
A first frequency conversion / quantization unit for frequency-converting and quantizing the watermarked image generated by the image synthesis unit;
A second frequency conversion / quantization unit for frequency-converting and quantizing the original image;
A difference extraction unit for extracting data obtained by subtracting the data calculated by the first frequency conversion / quantization unit from the data calculated by the second frequency conversion / quantization unit;
A first compression encoding unit for compressing and encoding data by the first frequency transform / quantization unit;
An image encoding apparatus comprising: a third compression encoding unit that compresses and encodes the data extracted by the difference extraction unit. An image composition unit that synthesizes an original image and a watermark image to generate a watermarked image;
A first frequency conversion / quantization unit for frequency-converting and quantizing the watermarked image generated by the image synthesis unit;
A second frequency conversion / quantization unit for frequency-converting and quantizing the original image;
Of the data calculated by the second frequency conversion / quantization unit, a difference extraction unit that extracts data of a portion different from the data calculated by the first frequency conversion / quantization unit;
A difference extraction unit that extracts data obtained by subtracting data from the first frequency transformation / quantization unit from data from the second frequency transformation / quantization unit;
A first compression encoding unit for compressing and encoding data by the first frequency transform / quantization unit;
A second compression encoding unit for compressing and encoding the data extracted by the difference extraction unit;
A third compression encoding unit for compressing and encoding the data extracted by the difference extraction unit;
A data selection unit that compares the data compression-encoded by the second compression-encoding unit with the data compression-encoded by the third compression-encoding unit and selects data with a small amount of data; Image encoding device. The image encoding device according to any one of claims 1 to 3, further comprising a data encryption unit that encrypts the difference extraction unit or the data extracted by the difference extraction unit. . A first compression decoding unit that compresses and decodes an encoded image that has been subjected to frequency conversion, quantization, and compression encoding for the watermarked image obtained by combining the original image and the watermark image;
A second compression decoding unit that compresses and decodes an encoded image obtained by compressing and encoding a portion different from the watermarked image in the data quantized by frequency conversion of the original image;
Of the data compressed and decoded by the first compression decoding unit, the data corresponding to the data compressed and decoded by the second compression decoding unit is converted by the second compression decoding unit. Difference restoration part to replace with data,
An image decoding apparatus comprising: an inverse quantization / frequency inverse transform unit that performs inverse quantization / frequency inverse transform on data by the difference restoration unit. A first compression decoding unit that compresses and decodes an encoded image that has been subjected to frequency conversion, quantization, and compression encoding for the watermarked image obtained by combining the original image and the watermark image;
A second compression / decoding unit that compresses and decodes an encoded image obtained by subtracting data obtained by frequency-converting and quantizing the watermarked image from data obtained by frequency-converting and quantizing the original image When,
Of the data compressed and decoded by the first compression / decoding unit, the data corresponding to the data compressed and decoded by the second compression / decoding unit is used by the second compression / decoding unit. A differential restoration unit for adding data;
An image decoding apparatus comprising: an inverse quantization / frequency inverse transform unit that performs inverse quantization / frequency inverse transform on data by the difference restoration unit. A first compression decoding unit that compresses and decodes an encoded image that has been subjected to frequency conversion, quantization, and compression encoding for the watermarked image obtained by combining the original image and the watermark image;
Of the data quantized by frequency conversion of the original image, the watermarked image is quantized by frequency conversion of the encoded image obtained by compression-encoding a portion different from the watermarked image or the original image data. A second compression decoding unit that compresses and decodes an encoded image obtained by subtracting the converted data and performing compression encoding;
Of the data compressed and decoded by the first compression decoding unit, the data corresponding to the data compressed and decoded by the second compression decoding unit is processed by the second compression decoding unit. Difference restoration part to replace with data,
A difference restoring unit that adds data by the second compression decoding unit to data of a portion corresponding to data by the second compression decoding unit among the data by the first compression decoding unit;
A data determination unit that selects processing by the difference restoration unit or the difference restoration unit based on data by a second compression decoding unit;
An image decoding apparatus comprising: the difference restoration unit or an inverse quantization / frequency inverse transform unit that performs inverse quantization / frequency inverse transform on data by the difference restoration unit. An encryption / decryption unit for canceling the encryption when the encoded image is encrypted,
The said 2nd compression decoding part compresses and decodes the encoding image by which encryption was cancelled | released by the said encryption decoding part, The one of Claims 5-7 characterized by the above-mentioned. Image encoding device. An image encoding device that generates an encoded image by encoding a watermarked image obtained by combining an original image and a watermark image, and an image decoding that decodes the encoded image generated by the image encoding device to generate a restored image In an image encoding / decoding system including an encoding device,
The image encoding device includes:
An image synthesis unit that synthesizes the original image and the watermark image to generate a watermarked image;
A first frequency conversion / quantization unit for frequency-converting and quantizing the watermarked image generated by the image synthesis unit;
A second frequency conversion / quantization unit for frequency-converting and quantizing the original image;
Of the data calculated by the second frequency conversion / quantization unit, a difference extraction unit that extracts data of a portion different from the data calculated by the first frequency conversion / quantization unit;
A first compression encoding unit for compressing and encoding data by the first frequency transform / quantization unit;
A second compression encoding unit that compresses and encodes the data extracted by the difference extraction unit;
The image decoding device includes:
A first compression decoding unit for compressing and decoding data compressed and encoded by the first compression encoding unit;
A second compression decoding unit for compressing and decoding the data compressed and encoded by the second compression encoding unit;
Of the data compressed and decoded by the first compression decoding unit, the data corresponding to the data compressed and decoded by the second compression decoding unit is converted by the second compression decoding unit. Difference restoration part to replace with data,
An image encoding / decoding system comprising: an inverse quantization / frequency inverse transform unit that performs inverse quantization / frequency inverse transform on data by the difference restoration unit. An image encoding device that generates an encoded image by encoding a watermarked image obtained by combining an original image and a watermark image, and an image decoding that decodes the encoded image generated by the image encoding device to generate a restored image In an image encoding / decoding system including an encoding device,
The image encoding device includes:
An image composition unit that synthesizes the original image and a watermark image to generate a watermarked image;
A first frequency conversion / quantization unit for frequency-converting and quantizing the watermarked image generated by the image synthesis unit;
A second frequency conversion / quantization unit for frequency-converting and quantizing the original image;
A difference extraction unit for extracting data obtained by subtracting the data calculated by the first frequency conversion / quantization unit from the data calculated by the second frequency conversion / quantization unit;
A first compression encoding unit for compressing and encoding data by the first frequency transform / quantization unit;
A third compression encoding unit that compresses and encodes the data extracted by the difference extraction unit;
The image decoding device includes:
A first compression decoding unit for compressing and decoding data compressed and encoded by the first compression encoding unit;
A second compression decoding unit for compressing and decoding the data compressed and encoded by the third compression encoding unit;
Of the data compressed and decoded by the first compression / decoding unit, the data corresponding to the data compressed and decoded by the second compression / decoding unit is used by the second compression / decoding unit. A differential restoration unit for adding data;
An image encoding / decoding system comprising: an inverse quantization / frequency inverse transform unit that performs inverse quantization / frequency inverse transform on data by the difference restoration unit. An image encoding device that generates an encoded image by encoding a watermarked image obtained by combining an original image and a watermark image, and an image decoding that decodes the encoded image generated by the image encoding device to generate a restored image In an image encoding / decoding system including an encoding device,
The image encoding device includes:
An image composition unit that synthesizes the original image and a watermark image to generate a watermarked image;
A first frequency conversion / quantization unit for frequency-converting and quantizing the watermarked image generated by the image synthesis unit;
A second frequency conversion / quantization unit for frequency-converting and quantizing the original image;
Of the data calculated by the second frequency conversion / quantization unit, a difference extraction unit that extracts data of a portion different from the data calculated by the first frequency conversion / quantization unit;
A difference extraction unit that extracts data obtained by subtracting data from the first frequency transformation / quantization unit from data from the second frequency transformation / quantization unit;
A first compression encoding unit for compressing and encoding data by the first frequency transform / quantization unit;
A second compression encoding unit for compressing and encoding the data extracted by the difference extraction unit;
A third compression encoding unit for compressing and encoding the data extracted by the difference extraction unit;
A data selection unit that compares the data compression-encoded by the second compression-encoding unit with the data compression-encoded by the third compression-encoding unit and selects data with a small amount of data; ,
The image decoding device includes:
A first compression decoding unit for compressing and decoding data compressed and encoded by the first compression encoding unit;
A second compression decoding unit for compressing and decoding the data selected by the data selection unit;
Of the data compressed and decoded by the first compression decoding unit, the data corresponding to the data compressed and decoded by the second compression decoding unit is processed by the second compression decoding unit. Difference restoration part to replace with data,
A difference restoring unit that adds data by the second compression decoding unit to data of a portion corresponding to data by the second compression decoding unit among the data by the first compression decoding unit;
A data determination unit that selects processing by the difference restoration unit or the difference restoration unit based on data by a second compression decoding unit;
An image encoding / decoding system comprising: the difference restoration unit or an inverse quantization / frequency inverse transform unit that performs inverse quantization / frequency inverse transform on data by the difference restoration unit. An image compositing step for compositing the original image and the watermark image to generate a watermarked image;
A first frequency conversion / quantization step for frequency-converting and quantizing the watermarked image generated in the image synthesis step;
A second frequency conversion / quantization step of frequency-converting and quantizing the original image;
Of the data calculated in the second frequency conversion / quantization step, a difference extraction step of extracting data of a portion different from the data calculated in the first frequency conversion / quantization step;
A first compression encoding step for compressing and encoding data in the first frequency conversion / quantization step;
And a second compression encoding step for compression encoding the data extracted in the difference extraction step. An image synthesis step of synthesizing the original image and the watermark image to generate a watermarked image;
A first frequency conversion / quantization step for frequency-converting and quantizing the watermarked image generated in the image synthesis step;
A second frequency conversion / quantization step of frequency-converting and quantizing the original image;
A difference extraction step of extracting data obtained by subtracting the data calculated in the first frequency conversion / quantization step from the data calculated in the second frequency conversion / quantization step;
A first compression encoding step for compressing and encoding data in the first frequency conversion / quantization step;
And a third compression encoding step for compressing and encoding the data extracted in the difference extraction step. An image synthesis step of synthesizing the original image and the watermark image to generate a watermarked image;
A first frequency conversion / quantization step for frequency-converting and quantizing the watermarked image generated in the image synthesis step;
A second frequency conversion / quantization step of frequency-converting and quantizing the original image;
Of the data calculated in the second frequency conversion / quantization step, a difference extraction step of extracting data of a portion different from the data calculated in the first frequency conversion / quantization step;
A difference extraction step of extracting data obtained by subtracting data in the first frequency conversion / quantization step from data in the second frequency conversion / quantization step;
A first compression encoding step for compressing and encoding data in the first frequency conversion / quantization step;
A second compression encoding step for compression encoding the data extracted in the difference extraction step;
A third compression encoding step for compression encoding the data extracted in the difference extraction step;
An image code comprising: a data selection step for comparing the data compression-encoded in the second compression-encoding step with the data compression-encoded in the third compression-encoding step and outputting data with a small amount of data Method. A first compression decoding step of compressing and decoding an encoded image obtained by frequency-converting and quantizing and compressing an original image and a watermarked image obtained by combining the watermark image;
A second compression decoding step for compressing and decoding an encoded image obtained by compression encoding a step different from the watermarked image in the data quantized by frequency conversion of the original image;
Of the data compressed and decoded in the first compression decoding step, the data corresponding to the data compressed and decoded in the second compression decoding step is converted into data in the second compression decoding step. A difference restoration step to replace,
An image decoding method comprising: an inverse quantization / frequency inverse transform step of inverse quantization / frequency inverse transform of data in the difference restoration step. A first compression decoding step of compressing and decoding an encoded image obtained by frequency-converting and quantizing and compressing an original image and a watermarked image obtained by combining the watermark image;
A second compression decoding step for compressing and decoding an encoded image obtained by subtracting data obtained by frequency converting and quantizing the watermarked image from data obtained by frequency converting and quantizing the original image; When,
Of the data compressed and decoded in the first compression decoding step, the data in the second compression decoding step is added to the data corresponding to the data compressed and decoded in the second compression decoding step. A difference restoration step to add,
An image decoding method comprising: an inverse quantization / frequency inverse transform step for inverse quantization / frequency inverse transform of data in the difference restoration step. A first compression decoding step of compressing and decoding an encoded image obtained by frequency-converting and quantizing and compressing an original image and a watermarked image obtained by combining the watermark image;
Of the data quantized by frequency conversion of the original image, the watermarked image is quantized by frequency conversion of the encoded image obtained by compression-encoding a portion different from the watermarked image or the original image data. A second compression decoding step of compressing and decoding the encoded image obtained by subtracting the converted data and compression encoding;
Of the data compressed and composited in the first compression decoding step, the data corresponding to the data compressed and composited in the second compression decoding step is converted into data in the second compression decoding step. A difference restoration step to replace,
A difference restoration step of adding the data in the second compression decoding step to the data corresponding to the data in the second compression decoding step among the data in the first compression decoding step;
A data determination step for selecting the difference restoration step or the processing by the difference restoration step based on the data in the second compression decoding step;
An image decoding method comprising: the difference restoration step or an inverse quantization / frequency inverse transformation step for inverse quantization / frequency inverse transformation of data in the difference restoration step.

Images