Image encoding method and device, image decoding method and device, and imaging device

1. An image encoding method, which is performed using a processor, for encoding, from a pixel value of a pixel quantized in m-bit accuracy and which is included in a pixel array where a plurality of pixels are arrayed, a pixel value quantized in n-bit accuracy, where n-bit is smaller than m-bit, the image encoding method comprising:

determining whether a pixel value of a pixel to be encoded is a specific pixel value;

when the pixel value of the pixel to be encoded is the specific pixel value,

encoding the pixel value of the pixel to be encoded by allocating a specific quantized representative value included in a range of quantized representative values to the pixel to be encoded, the range of the quantized representative values including a quantized representative value which is quantized in n-bit accuracy from the pixel value of the pixel to be encoded; and

when the pixel value of the pixel to be encoded is other than the specific pixel value,

adding a predetermined offset value to the pixel value of the pixel to be encoded, and

encoding the pixel value of the pixel to be encoded by allocating a quantized representative value other than the specific quantized representative value to the pixel value to be encoded, the range of the quantized representative values including the quantized representative value other than the specific quantized representative value.

2. The image encoding method according to claim 1 , wherein the predetermined offset value is 2 (m−n) −1.

3. An image encoding method, which is performed using a processor, for encoding, from a pixel value of a pixel quantized in m-bit accuracy and which is included in a pixel array where a plurality of pixels are arrayed, a pixel value quantized in n-bit accuracy, where n-bit is smaller than m-bit, the image encoding method comprising:

calculating a difference value between a pixel value of a pixel to be encoded and a pixel value of a pixel adjacent to the pixel to be encoded;

setting a quantized width used at the time of quantizing in n-bit accuracy according to the size of the difference value and a quantized representative value which is quantized in n-bit accuracy from the difference value;

determining whether the pixel value of the pixel adjacent to the pixel to be encoded is a specific pixel value;

when the pixel value of the pixel adjacent to the pixel to be encoded is not the specific pixel value, quantizing the difference value in n-bit accuracy by using the quantized width; and

when the pixel value of the pixel adjacent to the pixel to be encoded is the specific pixel value, quantizing the difference value by allocating a specific quantized representative value included in a range of quantized representative values to the difference value, the range of the quantized representative values including the quantized representative value quantized in n-bit accuracy from the difference value.

4. The image encoding method according to claim 3 ,

wherein when the pixel value of the pixel adjacent to the pixel to be encoded is not the specific pixel value, the quantizing the difference value by allocating the specific quantized representative value included in the range of the quantized representative values to the difference value includes:

changing the quantized width to a quantized width larger than the quantized width; and

quantizing the difference value in n-bit accuracy by using the changed quantized width.

5. The image encoding method according to claim 3 ,

wherein when the pixel value of the pixel adjacent to the pixel to be encoded is not the specific pixel value, the quantizing the difference value by allocating the specific quantized representative value included in the range of the quantized representative values to the difference value includes:

quantizing the difference value in n-bit accuracy by allocating a quantized representative value other than the specific quantized representative value included in the range of the quantized representative values.

6. The image encoding method according to claim 3 , further comprising

selecting a pixel having a pixel value other than the specific value as the pixel to be encoded.

7. The image encoding method according to claim 3 ,

wherein the pixel array has pixels of at least two types of colors arrayed therein, and

wherein the pixel adjacent to the pixel to be encoded has the same color as the pixel to be encoded.

8. The image encoding method according to claim 3 ,

wherein the pixel array has pixels of at least two types of colors arrayed therein, and

wherein the pixel adjacent to the pixel to be encoded has a different color other than the color of the pixel to be encoded.

9. The image encoding method according to claim 1 , further comprising

packing the pixel array including the plurality of pixels, each pixel having a quantized representative value quantized in n-bit accuracy, by multiples of a memory access bit width.

10. An image encoding device for encoding, from a pixel value of a pixel quantized in m-bit accuracy and which is included in a pixel array where a plurality of pixels are arrayed, a pixel value quantized in n-bit accuracy, where n-bit is smaller than m-bit, the image encoding device comprising:

a specific pixel value determining unit that determines whether a pixel value of a pixel to be encoded is a specific pixel value;

an encoding unit that (i) when the pixel value of the pixel to be encoded is the specific pixel value, performs encoding of the pixel value of the pixel to be encoded by allocating a specific quantized representative value included in a range of quantized representative values to the pixel to be encoded, the range of the quantized representative values including a quantized representative value which is quantized in n-bit accuracy from the pixel value of the pixel to be encoded, and (ii) when the pixel value of the pixel to be encoded is other than the specific pixel value, performs encoding of the pixel value of the pixel to be encoded by allocating a quantized representative value other than the specific quantized representative value, the range of the quantized representative values including the quantized representative value other than the specific quantized representative value; and

an adding unit that adds, when the pixel value of the pixel to be encoded is other than the specific pixel value, a predetermined offset value to the pixel value of the pixel to be encoded prior to encoding the pixel value of the pixel to be encoded.

11. An image encoding device for encoding, from a pixel value of a pixel quantized in m-bit accuracy and which is included in a pixel array where a plurality of pixels are arrayed, a pixel value quantized in n-bit accuracy, where n-bit is smaller than m-bit, the image encoding device comprising:

a difference value calculating unit that calculates a difference value between a pixel value of a pixel to be encoded and a pixel value of a pixel adjacent to the pixel to be encoded;

a setting unit that sets a quantized width used at the time of quantizing in n-bit accuracy according to the size of the difference value and a quantized representative value which is quantized in n-bit accuracy from the difference value;

a specific pixel value determining unit that determines whether the pixel value of the pixel adjacent to the pixel to be encoded is a specific pixel value; and

an encoding unit that (i) when the pixel value of the pixel adjacent the pixel to be encoded is the specific pixel value, quantizes the difference value in n-bit accuracy by using the quantized width, and (ii) when the pixel value of the pixel adjacent to the pixel to be encoded is other than the specific pixel value, quantizes the difference value by allocating a specific quantized representative value included in a range of quantized representative values to the difference value, the range of the quantized representative values including the quantized representative value quantized in n-bit accuracy from the difference value.