Image processing apparatus and method
View Patent ↗There is provided an image processing apparatus including a quantization unit that quantizes an image subjected to logarithmic conversion such that a quantization error is focused on a luminance region in which expansion of an error caused due to logarithmic inverse-conversion which is inverse conversion of the logarithmic conversion is relatively small or a luminance region in which no expansion of the error occurs; and an encoding unit that encodes an index image obtained through the quantization by the quantization unit.
1. An image processing apparatus comprising:
a quantization unit that quantizes an image subjected to logarithmic conversion such that a quantization error is focused on a luminance region in which expansion of an error caused due to logarithmic inverse-conversion which is inverse conversion of the logarithmic conversion is relatively small or a luminance region in which no expansion of the error occurs; and
an encoding unit that encodes an index image obtained through the quantization by the quantization unit.
2. The image processing apparatus according to claim 1 , wherein the quantization unit includes
a histogram generation unit that generates a histogram of each luminance value of the image subjected to the logarithmic conversion,
a luminance region division unit that divides an entire luminance region of the histogram generated by the histogram generation unit into a plurality of partial luminance regions,
a table generation unit that generates a quantization table indicating a correspondence relation between each luminance value and an index value and a representative value table indicating a correspondence relation between each index value and a representative value of each class for each of the partial luminance regions divided from the entire luminance region by the luminance region division unit, and
an index image generation unit that generates the index image by quantizing the image subjected to the logarithmic conversion using the quantization table for each partial luminance region generated by the table generation unit.
3. The image processing apparatus according to claim 2 , wherein the table generation unit generates the quantization table and the representative value table such that, among the plurality of partial luminance regions, the quantization error is focused on the partial luminance region in which the expansion of the error caused due to the logarithmic inverse-conversion is relatively small or the partial luminance region in which no expansion of the error occurs.
4. The image processing apparatus according to claim 3 , wherein the table generation unit generates the quantization table and the representative value table for the partial luminance region in which the expansion of the error caused due to the logarithmic inverse-conversion is relatively small or the partial luminance region in which no expansion of the error occurs in accordance with a quantization method in which the quantization error occurs, and generates the quantization table and the representative value table for the other partial luminance regions in accordance with a quantization method in which the quantization error does not occur.
5. The image processing apparatus according to claim 4 ,
wherein the luminance region division unit divides, using a predetermined division point as a boundary, the entire luminance region of the histogram into a low-luminance region of low luminance from the predetermined division point and a high-luminance region of high luminance from the predetermined division point, and
wherein the table generation unit generates the quantization table and the representative value table of Lloyd-Max quantization for the low-luminance region in which the expansion of the error caused due to the logarithmic inverse-conversion is relatively small or the low-luminance region in which no expansion of the error occurs, and generates the quantization table and the representative value table of reversible quantization for the high-luminance region in which the expansion of the error caused due to the logarithmic inverse-conversion is relatively large.
6. The image processing apparatus according to claim 5 , wherein the encoding unit encodes the representative value table generated by the table generation unit.
7. The image processing apparatus according to claim 6 , wherein the encoding unit adds encoded data of the generated representative value table to encoded data of the generated index image.
8. The image processing apparatus according to claim 6 , wherein the encoding unit associates encoded data of the generated representative value table with encoded data of the generated index image.
9. The image processing apparatus according to claim 5 ,
wherein the quantization unit further includes a division point setting unit that sets the division point, and
wherein the luminance region division unit divides the entire luminance region of the histogram into the low-luminance region and the high-luminance region using the division point set by the division point setting unit as the boundary.
10. The image processing apparatus according to claim 1 , wherein the encoding unit encodes the index image in conformity with a JPEG2000 scheme.
11. The image processing apparatus according to claim 1 , wherein the image is a high dynamic range image.
12. The image processing apparatus according to claim 1 , further comprising:
a logarithmic conversion unit that performs the logarithmic conversion on an image to be encoded,
wherein the quantization unit quantizes the image subjected to the logarithmic conversion by the logarithmic conversion unit such that the quantization error is focused on the luminance region in which the expansion of the error caused due to the logarithmic inverse-conversion is relatively small or the luminance region in which no expansion of the error occurs.
13. The image processing apparatus according to claim 12 , further comprising:
an integer conversion unit that performs floating point number-to-integer conversion on the image subjected to the logarithmic conversion by the logarithmic conversion unit and expressed by a floating point number,
wherein the quantization unit quantizes the image subjected to the floating point number-to-integer conversion by the integer conversion unit such that the quantization error is focused on the luminance region in which the expansion of the error caused due to the logarithmic inverse-conversion is relatively small or the luminance region in which no expansion of the error occurs.
14. An image processing method of an image processing apparatus, comprising:
quantizing, by a quantization unit, an image subjected to logarithmic conversion such that a quantization error is focused on a luminance region in which expansion of an error caused due to logarithmic inverse-conversion which is inverse conversion of the logarithmic conversion is relatively small or a luminance region in which no expansion of the error occurs; and
encoding, by an encoding unit, an index image obtained through the quantization.
15. An image processing apparatus comprising:
a decoding unit that decodes encoded data generated by encoding an index image which is obtained through quantization performed on an image subjected to logarithmic conversion such that a quantization error is focused on a luminance region in which expansion of an error caused due to logarithmic inverse-conversion which is inverse conversion of the logarithmic conversion is relatively small or a luminance region in which no expansion of the error occurs in accordance with a method corresponding to the encoding of generating the encoded data; and
an inverse-quantization unit that performs inverse quantization corresponding to the quantization on the index image obtained by decoding the encoded data by the decoding unit.
16. The image processing apparatus according to claim 15 , wherein the decoding unit decodes not only the encoded data of the index image but also encoded data of a representative value table corresponding to a quantization table applied in the quantization.
17. The image processing apparatus according to claim 16 , wherein the inverse-quantization unit performs the inverse quantization on the index image using the representative value table decoded by the decoding unit.
18. The image processing apparatus according to claim 17 , further comprising:
a floating point number conversion unit that performs integer-to-floating point number conversion on the image obtained by performing the inverse quantization on the index image by the inverse-quantization unit and expressed by an integer.
19. The image processing apparatus according to claim 18 , further comprising:
a logarithmic inverse-conversion unit that performs logarithmic inverse-conversion on the image obtained through the integer-to-floating point number conversion by the floating point number conversion unit and expressed by a floating point number.
20. An image processing method of an image processing apparatus, comprising:
decoding, by a decoding unit, encoded data generated by encoding an index image which is obtained through quantization performed on an image subjected to logarithmic conversion such that a quantization error is focused on a luminance region in which expansion of an error caused due to logarithmic inverse-conversion which is inverse conversion of the logarithmic conversion is relatively small or a luminance region in which no expansion of the error occurs in accordance with a method corresponding to the encoding of generating the encoded data; and
performing, by an inverse-quantization unit, inverse quantization corresponding to the quantization on the index image obtained by decoding the encoded data.