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/*! @file companding.c
*
* @brief Implementation of the routines for computing the companding curves
* that is applied to the quantized coefficient magnitudes.
*
* @version 1.0.0
*
* (C) Copyright 2018 GoPro Inc (http://gopro.com/).
*
* Licensed under either:
* - Apache License, Version 2.0, http://www.apache.org/licenses/LICENSE-2.0
* - MIT license, http://opensource.org/licenses/MIT
* at your option.
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "common.h"
//TODO: Change the companding parameter into a global constant
#ifndef COMPANDING
#define COMPANDING 1
#define COMPANDING_MORE (54) // Zero means no companding (54 is a good value)
#endif
/*!
@brief Maximum coefficient magnitude in the codebook
@todo Need to calculate the maximum value from the codebook
*/
const int maximum_codebook_value = 255;
/*!
@brief Apply the default companding curve to the specified value
Note that this companding curve has been superceeded by the cubic curve.
*/
int32_t CompandedValue(int32_t value)
{
const int midpoint_rounding = 2;
int32_t magnitude = absolute(value);
#if COMPANDING
if (magnitude >= 40)
{
magnitude -= 40;
magnitude += midpoint_rounding;
magnitude >>= 2;
magnitude += 40;
#if COMPANDING_MORE
if (magnitude >= COMPANDING_MORE)
{
magnitude -= COMPANDING_MORE;
magnitude += midpoint_rounding;
magnitude >>= 2;
magnitude += COMPANDING_MORE;
}
#endif
}
#endif
// Restore the sign to the companded value
return ((value >= 0) ? magnitude : neg(magnitude));
}
/*!
@brief Return the parameter that controls the companding curve
This parameter does not apply if the cubic companding curve is used.
*/
uint32_t CompandingParameter()
{
return COMPANDING_MORE;
}
/*!
@brief Compute a table of values for the cubic companding curve
The companding curve is f(x) = x + (x ^ 3 / (255 ^ 3)) * 768
so the range of coefficient magnitudes from 0 to 255 becomess 0 to 1023.
*/
CODEC_ERROR ComputeCubicTable(int16_t cubic_table[], int cubic_table_length, int16_t maximum_value)
{
size_t cubic_table_size = cubic_table_length * sizeof(cubic_table[0]);
int last_cubic_table_index = cubic_table_length - 2;
int16_t last_magnitude;
int16_t index;
// Clear the cubic table
memset(cubic_table, 0, cubic_table_size);
for (index = 1; index <= maximum_value; index++)
{
double cubic = index;
int magnitude = index;
cubic *= index;
cubic *= index;
cubic *= 768;
//cubic /= 256*256*256;
cubic /= 255*255*255;
magnitude += (int)cubic;
//if (mag > 1023) mag = 1023;
if (magnitude > last_cubic_table_index) {
magnitude = last_cubic_table_index;
}
cubic_table[magnitude] = index;
}
// Fill unused entries in the cubic table
last_magnitude = 0;
for (index = 0; index < cubic_table_length; index++)
{
if (cubic_table[index])
{
last_magnitude = cubic_table[index];
}
else
{
cubic_table[index] = last_magnitude;
}
}
return CODEC_ERROR_OKAY;
}
/*!
@brief Invert the companding curve applied during encoding
*/
int32_t UncompandedValue(int32_t value)
{
#if 1 //CUBIC_COMPANDING
double cubic;
int32_t magnitude = absolute(value);
cubic = magnitude;
cubic *= magnitude;
cubic *= magnitude;
cubic *= 768;
//cubic /= 256*256*256;
cubic /= 255*255*255;
magnitude += (int32_t)cubic;
// Restore the sign
value = ((value < 0) ? neg(magnitude) : magnitude);
#else
if (40 <= value && value < 264)
{
#if COMPANDING_MORE
if (value >= COMPANDING_MORE)
{
value -= COMPANDING_MORE;
value <<= 2;
value += COMPANDING_MORE;
}
#endif
value -= 40;
value <<= 2;
value += 40;
}
else if (value <= -40)
{
// Apply the inverse companding formula to the absolute value
value = -value;
#if COMPANDING_MORE
if (value >= COMPANDING_MORE)
{
value -= COMPANDING_MORE;
value <<= 2;
value += COMPANDING_MORE;
}
#endif
value -= 40;
value <<= 2;
value += 40;
// Restore the sign
value = -value;
}
#endif
return value;
}
/*!
@brief Invert the companding curve applied to a pixel
*/
PIXEL UncompandedPixel(PIXEL value)
{
#if 1 //CUBIC_COMPANDING
double cubic;
int32_t magnitude = absolute(value);
cubic = magnitude;
cubic *= magnitude;
cubic *= magnitude;
cubic *= 768;
//cubic /= 256*256*256;
cubic /= 255*255*255;
magnitude += (int32_t)cubic;
// Restore the sign
value = ClampPixel((value < 0) ? neg(magnitude) : magnitude);
#else
if (40 <= value && value < 264)
{
#if COMPANDING_MORE
if (value >= COMPANDING_MORE)
{
value -= COMPANDING_MORE;
value <<= 2;
value += COMPANDING_MORE;
}
#endif
value -= 40;
value <<= 2;
value += 40;
}
else if (value <= -40)
{
// Apply the inverse companding formula to the absolute value
value = neg(value);
#if COMPANDING_MORE
if (value >= COMPANDING_MORE)
{
value -= COMPANDING_MORE;
value <<= 2;
value += COMPANDING_MORE;
}
#endif
value -= 40;
value <<= 2;
value += 40;
// Restore the sign
value = neg(value);
}
#endif
return value;
}
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