kc3-lang/libjpeg-turbo/jdscale.c

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• Hash : 2e8360e0
  Author :
  Date : 1999-04-27T00:00:00
  

  IJG's JPEG software v6b with lossless JPEG support
  
  Patch obtained from:
  https://sourceforge.net/projects/jpeg/files/ftp.oceana.com
  
  Author date taken from original announcement and timestamp of patch
  tarball:
  https://groups.google.com/g/comp.protocols.dicom/c/rrkP8BxoMRk/m/Ij4dfprggp8J
  

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• jdscale.c

• /*
   * jdscale.c
   *
   * Copyright (C) 1998, Thomas G. Lane.
   * This file is part of the Independent JPEG Group's software.
   * For conditions of distribution and use, see the accompanying README file.
   *
   * This file contains sample scaling for lossless JPEG.  This is a
   * combination of upscaling the undifferenced sample by 2^Pt and downscaling
   * the sample to fit into JSAMPLE.
   */
  
  #define JPEG_INTERNALS
  #include "jinclude.h"
  #include "jpeglib.h"
  #include "jlossls.h"		/* Private declarations for lossless codec */
  
  
  #ifdef D_LOSSLESS_SUPPORTED
  
  /*
   * Private scaler object for lossless decoding.
   */
  
  typedef struct {
    int scale_factor;
  } scaler;
  
  typedef scaler * scaler_ptr;
  
  
  /*
   * Scalers for packing sample differences into JSAMPLEs.
   */
  
  METHODDEF(void)
  simple_upscale(j_decompress_ptr cinfo,
  	       JDIFFROW diff_buf, JSAMPROW output_buf,
  	       JDIMENSION width)
  {
    j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
    scaler_ptr scaler = (scaler_ptr) losslsd->scaler_private;
    int scale_factor = scaler->scale_factor;
    int xindex;
  
    for (xindex = 0; xindex < width; xindex++)
      output_buf[xindex] = (JSAMPLE) (diff_buf[xindex] << scale_factor);
  }
  
  METHODDEF(void)
  simple_downscale(j_decompress_ptr cinfo,
  		 JDIFFROW diff_buf, JSAMPROW output_buf,
  		 JDIMENSION width)
  {
    j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
    scaler_ptr scaler = (scaler_ptr) losslsd->scaler_private;
    int scale_factor = scaler->scale_factor;
    int xindex;
  
    for (xindex = 0; xindex < width; xindex++)
      output_buf[xindex] = (JSAMPLE) RIGHT_SHIFT(diff_buf[xindex], scale_factor);
  }
  
  METHODDEF(void)
  noscale(j_decompress_ptr cinfo,
  	JDIFFROW diff_buf, JSAMPROW output_buf,
  	JDIMENSION width)
  {
    int xindex;
  
    for (xindex = 0; xindex < width; xindex++)
      output_buf[xindex] = (JSAMPLE) diff_buf[xindex];
  }
  
  
  METHODDEF(void)
  scaler_start_pass (j_decompress_ptr cinfo)
  {
    j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
    scaler_ptr scaler = (scaler_ptr) losslsd->scaler_private;
    int downscale;
  
    /*
     * Downscale by the difference in the input vs. output precision.  If the
     * output precision >= input precision, then do not downscale.
     */
    downscale = BITS_IN_JSAMPLE < cinfo->data_precision ?
      cinfo->data_precision - BITS_IN_JSAMPLE : 0;
  
    scaler->scale_factor = cinfo->Al - downscale;
  
    /* Set scaler functions based on scale_factor (positive = left shift) */
    if (scaler->scale_factor > 0)
      losslsd->scaler_scale = simple_upscale;
    else if (scaler->scale_factor < 0) {
      scaler->scale_factor = -scaler->scale_factor;
      losslsd->scaler_scale = simple_downscale;
    }
    else
      losslsd->scaler_scale = noscale;
  }
  
  
  GLOBAL(void)
  jinit_d_scaler (j_decompress_ptr cinfo)
  {
    j_lossless_d_ptr losslsd = (j_lossless_d_ptr) cinfo->codec;
    scaler_ptr scaler;
  
    scaler = (scaler_ptr)
      (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
  				SIZEOF(scaler));
    losslsd->scaler_private = (void *) scaler;
    losslsd->scaler_start_pass = scaler_start_pass;
  }
  
  #endif /* D_LOSSLESS_SUPPORTED */
  
  

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