Device and method of improving the perceptual luminance nonlinearity-based image data exchange across different display capabilities
A handheld imaging device has a data receiver that is configured to receive reference encoded image data. The data includes reference code values, which are encoded by an external coding system. The reference code values represent reference gray levels, which are being selected using a reference grayscale display function that is based on perceptual non-linearity of human vision adapted at different light levels to spatial frequencies. The imaging device also has a data converter that is configured to access a code mapping between the reference code values and device-specific code values of the imaging device. The device-specific code values are configured to produce gray levels that are specific to the imaging device. Based on the code mapping, the data converter is configured to transcode the reference encoded image data into device-specific image data, which is encoded with the device-specific code values.
1. A method comprising:
receiving, by a data encoder, image data to be encoded;
accessing, via the data encoder, a reference data conversion function which determines a mapping between a set of reference digital code values and a set of reference levels based on contrast sensitivity of human vision;
based on the receiving and the accessing, encoding, via the data encoder, the received image data into reference encoded image data; and
outputting, via the data encoder, the reference encoded image data,
wherein:
color component values in the received image data are represented by the set of reference digital code values, the reference digital code values having a bit depth of 10 or 12 bits,
at least a lowest three and a highest three reference digital code values are excluded from the mapping,
the mapping is based at least in part on a functional model of:
(
c
1
+
c
2
Y
n
1
+
c
3
Y
n
)
m
,
and
n, m, c 1 , c 2 , and c 3 are predetermined values.
2. The method of claim 1 , wherein:
n
=
2610
4096
×
1
4
≃
0.1593017578125
;
m
=
2523
4096
×
128
≃
78.84375
;
c
1
=
c
3
-
c
2
+
1
=
3424
4096
≃
0.8359375
;
c
2
=
2413
4096
×
32
≃
18.8515625
;
and
c
3
=
2392
4096
×
32
≃
18.6875
.
3. The method of claim 1 , wherein the color component is at least one of R, G and B color components.
4. The method of claim 1 , wherein the color component is luminance (Y).
5. The method of claim 1 , further comprising a step of mapping, via the data encoder, of a digital code value in the image data to a normalized value V, wherein 0≦V≦1.
6. The method of claim 5 , wherein a relationship between the normalized value V and the digital code value D is provided by the function:
V
=
D
-
4.2
b
-
10
1015.2
b
-
10
wherein b is a bit depth corresponding to a number of bits used to represent the digital code value.
7. The method of claim 6 , wherein the digital code value D represents a sampled value of a component of the image data comprised in a serial digital interface (SDI) signal.
8. The method of claim 6 , wherein the bit depth is 10 bits and a table representative of the reference data conversion function is provided by Table 4 of the specification.
9. The method of claim 1 , wherein the image data comprises digital code values D which represent sampled values of a component of the image data, the image data being encoded in one of a high-resolution high dynamic range (HDR) image format, a RGB color space associated with the Academy Color Encoding Specification (ACES) standard of the Academy of Motion Picture Arts and Sciences (AMPAS), a P3 color space standard of the Digital Cinema initiative, a Reference Input Medium Metric/Reference Output Medium Metric (RIMM/ROMM) standard, an sRGB color space, or a RGB color space associated with the BT. 709 Recommendation standard of the International Telecommunications Union (ITU).