Conversion method and conversion apparatus

A conversion method for converting luminance of a video to be displayed on a display apparatus, the conversion method comprising:

• acquiring a first luminance signal indicating a first code value obtained by quantization of a luminance value of the video, the luminance value of the video being included in a first luminance range;
• and
• converting the first code value indicated by the acquired first luminance signal into a second luminance value compatible with a second luminance range, a maximum value of the second luminance range being determined based on a luminance range of the display apparatus, the maximum value of the second luminance range being smaller than a maximum value of the first luminance range, and the maximum value of the second luminance range being larger than 100 nit,
• wherein the converting the first code value comprises:
• by using an electro-optical transfer function (EOTF) that associates the luminance value in the first luminance range with a plurality of first code values, determining a first luminance value associated with the first code value indicated by the acquired first luminance signal, the first luminance value being compatible with the first luminance range;
• determining the second luminance value associated with the first luminance value in advance, the second luminance value being compatible with the second luminance range;
• and
• performing first luminance conversion to convert the first luminance value compatible with the first luminance range into the second luminance value compatible with the second luminance range,
• wherein the maximum value of the second luminance range is a maximum value of the luminance range of the display apparatus,
• wherein the performing the first luminance conversion comprises, when the first luminance value is a first maximum luminance value that is a maximum value of luminance values of a plurality of images that constitute the video, determining a second maximum luminance value that is the maximum value of the luminance of the display apparatus as the second luminance value,
• wherein the performing the first luminance conversion comprises:
• when the first luminance value is less than or equal to a first predetermined luminance value, converting the first luminance value into the second luminance value based on a conversion equation set for a low luminance region;
• when the first luminance value is greater than the first predetermined luminance value and less than a second predetermined value, converting the first luminance value into the second luminance value based on a conversion equation set for a middle luminance region;
• when the first luminance value is greater than or equal to the second predetermined luminance value, converting the first luminance value into the second luminance value based on a conversion equation set for a high luminance region, and
• wherein a locus of the conversion equation set for the low luminance region and a locus of the third conversion equation set for the high luminance region are linear, and a locus of the conversion equation set for the middle luminance region is curved.

A conversion apparatus for converting luminance of a video to be displayed on a display apparatus, the conversion apparatus comprising:

• one or more memories;
• and
• circuitry which, in operation performs:
• acquiring a first luminance signal indicating a first code value obtained by quantization of a luminance value of the video, the luminance value of the video being included in a first luminance range;
• and
• converting the first code value indicated by the acquired first luminance signal into a second luminance value compatible with a second luminance range, a maximum value of the second luminance range being determined based on a luminance range of the display apparatus, the maximum value of the second luminance range being smaller than a maximum value of the first luminance range, and the maximum value of the second luminance range being larger than 100 nit,
• wherein the converting the first code value comprises:
• by using an electro-optical transfer function (EOTF) that associates the luminance value in the first luminance range with a plurality of first code values, determining a first luminance value associated with the first code value indicated by the acquired first luminance signal, the first luminance value being compatible with the first luminance range;
• determining the second luminance value associated with the first luminance value in advance, the second luminance value being compatible with the second luminance range;
• and
• performing first luminance conversion to convert the first luminance value compatible with the first luminance range into the second luminance value compatible with the second luminance range,
• wherein the maximum value of the second luminance range is a maximum value of the luminance range of the display apparatus,
• wherein the performing the first luminance conversion comprises, when the first luminance value is a first maximum luminance value that is a maximum value of luminance values of a plurality of images that constitute the video, determining a second maximum luminance value that is the maximum value of the luminance of the display apparatus as the second luminance value,
• wherein the performing the first luminance conversion comprises:
• when the first luminance value is less than or equal to a first predetermined luminance value, converting the first luminance value into the second luminance value based on a conversion equation set for a low luminance region;
• when the first luminance value is greater than the first predetermined luminance value and less than a second predetermined value, converting the first luminance value into the second luminance value based on a conversion equation set for a middle luminance region;
• when the first luminance value is greater than or equal to the second predetermined luminance value, converting the first luminance value into the second luminance value based on a conversion equation set for a high luminance region, and wherein a locus of the conversion equation set for the low luminance region and a locus of the conversion equation set for the high luminance region are linear, and a locus of the conversion equation set for the middle luminance region is curved.