Method for outputting freshness information, freshness information output apparatus, and non-transitory computer-readable recording medium

1. A method for outputting freshness information, the method comprising the steps of:

obtaining, using a hardware processor, information indicating luminance of an iris portion of an eye of a fish onto which ultraviolet light is radiated; and

outputting, using the hardware processor, the freshness information indicating freshness of the fish on the basis of the foregoing information.

2. The method according to claim 1 , further comprising the steps of:

capturing an ultraviolet image of the eye of the fish onto which the ultraviolet light has been radiated; and

extracting a luminance value of the iris portion from the ultraviolet image, determining the freshness of the fish on the basis of the luminance value of the iris portion, and outputting the freshness information.

3. The method according to claim 2 ,

wherein, in the step of extracting, a luminance value of a crystalline lens portion is extracted from the ultraviolet image and the freshness of the fish is determined on the basis of a freshness index, which is obtained by normalizing the luminance value of the iris portion using the luminance value of the crystalline lens portion.

4. The method according to claim 3 ,

wherein, in the step of extracting, the freshness index is a difference between the luminance value of the iris portion and the luminance value of the crystalline lens portion, a value obtained by dividing the difference by the luminance value of the crystalline lens portion, or a ratio of the luminance value of the iris portion to the luminance value of the crystalline lens portion.

5. The method according to claim 4 ,

wherein the step of extracting includes the steps of (a) detecting an edge portion in the ultraviolet image, and (b) detecting a portion similar to a double-circle pattern from the detected edge portion,

wherein the double-circle pattern includes a first circle and a second circle having a radius larger than that of the first circle,

wherein a region inside the first circle includes the crystalline lens portion, and

wherein a region between an arc of the first circle and an arc of the second circle includes the iris portion.

6. The method according to claim 2 ,

wherein, in the step of capturing, the ultraviolet image is captured by radiating the ultraviolet light and an infrared image of the eye of the fish is captured by radiating infrared light, and

wherein, in the step of extracting, the freshness of the fish is determined in accordance with a freshness index, which is obtained by normalizing the luminance value of the iris portion extracted from the ultraviolet image using a luminance value of an iris portion extracted from the infrared image.

7. The method according to claim 6 ,

wherein, in the step of extracting, the freshness index is a difference between the luminance value of the iris portion extracted from the ultraviolet image and the luminance value of the iris portion extracted from the infrared image, a value obtained by dividing the difference by the luminance value of the iris portion extracted from the infrared image, or a ratio of the luminance value of the iris portion extracted from the ultraviolet image to the luminance value of the iris portion extracted from the infrared image.

8. The method according to claim 7 ,

wherein, in the step of extracting, the freshness of the fish is determined by referring to predetermined determination information, in which each of a plurality of different pieces of freshness information and each of a plurality of ranges of values of the freshness index are associated with each other.

9. The method according to claim 8 ,

wherein the freshness information is represented by time elapsed since a fish died, and

wherein the determination information is information in which a longer time elapsed since a fish died is associated with a range of larger values of the freshness index.

10. A freshness information output apparatus comprising:

an obtainer that obtains information indicating luminance of an iris portion of an eye of a fish onto which ultraviolet light has been radiated; and

an outputter that outputs freshness information indicating freshness of the fish determined on the basis of the foregoing information.

11. The freshness information output apparatus according to claim 10 , further comprising:

an ultraviolet light radiator that radiates the ultraviolet light; and

a mobile information device,

wherein the mobile information device includes an image capturer that captures an image at a time when the ultraviolet radiator radiates the ultraviolet light and an outputter that determines the freshness of the fish on the basis of a luminance value of the iris portion extracted from the image captured by the image capturer and that displays information indicating a result of the determination.

12. A non-transitory computer-readable recording medium storing a control program for causing a device including a processor to execute a process for determining freshness of a fish, the process comprising the steps of:

capturing an ultraviolet image of an eye of the fish onto which ultraviolet light has been radiated; and

extracting a luminance value of an iris portion from the ultraviolet image, determining the freshness of the fish on the basis of the luminance value of the iris portion, and outputting freshness information indicating a result of the determination.