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/*! @file logcurve.c
*
* @brief Implementation of functions used to do log conversion.
*
* @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"
uint16_t EncoderLogCurve[LOG_CURVE_TABLE_LENGTH];
uint16_t DecoderLogCurve[LOG_CURVE_TABLE_LENGTH];
void SetupDecoderLogCurve(void)
{
int i;
const int log_table_size = sizeof(DecoderLogCurve) / sizeof(DecoderLogCurve[0]);
const int max_16_bit = (1 << 16) - 1;
for( i = 0; i < log_table_size; i++ )
{
//input 12-bit, output 16-bit
float input = i;
float output = max_16_bit * (pow(113.0, input/4095.0) - 1.0)/112.0;
DecoderLogCurve[i] = minimum( (int)output, max_16_bit );
}
}
void SetupEncoderLogCurve(void)
{
int i;
const int max_input_val = LOG_CURVE_TABLE_LENGTH - 1;
for( i = 0; i < LOG_CURVE_TABLE_LENGTH; i++ )
{
//input 16-bit, output 12-bit
float input = maximum( 0, i );
float output = 4095.0 * (log10(input/max_input_val * 112.0 + 1.0)/log10(113));
EncoderLogCurve[i] = ( (uint16_t)output );
}
}
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