The Independent JPEG Group's JPEG software v1

1991-10-07 00:00:00 +00:00
commit 2cbeb8abd9
53 changed files with 13965 additions and 0 deletions
--- a/jbsmooth.c
+++ b/jbsmooth.c
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+/*
+ * jbsmooth.c
+ *
+ * Copyright (C) 1991, 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 cross-block smoothing routines.
+ * These routines are invoked via the smooth_coefficients method.
+ */
+
+#include "jinclude.h"
+
+#ifdef BLOCK_SMOOTHING_SUPPORTED
+
+
+/*
+ * Cross-block coefficient smoothing.
+ */
+
+METHODDEF void
+smooth_coefficients (decompress_info_ptr cinfo,
+		     jpeg_component_info *compptr,
+		     JBLOCKROW above,
+		     JBLOCKROW currow,
+		     JBLOCKROW below,
+		     JBLOCKROW output)
+{
+  QUANT_TBL_PTR Qptr = cinfo->quant_tbl_ptrs[compptr->quant_tbl_no];
+  long blocks_in_row = compptr->subsampled_width / DCTSIZE;
+  long col;
+
+  /* First, copy the block row as-is.
+   * This takes care of the first & last blocks in the row, the top/bottom
+   * special cases, and the higher-order coefficients in each block.
+   */
+  jcopy_block_row(currow, output, blocks_in_row);
+
+  /* Now apply the smoothing calculation, but not to any blocks on the
+   * edges of the image.
+   */
+
+  if (above != NULL && below != NULL) {
+    for (col = 1; col < blocks_in_row-1; col++) {
+
+      /* See section 13.10 of JPEG-8-R8, or K.8 of JPEG-9-R6.
+       *
+       * As I understand it, this produces approximations
+       * for the low frequency AC components, based on the
+       * DC values of the block and its eight neighboring blocks.
+       * (Thus it can't be used for blocks on the image edges.)
+       */
+
+      /* The layout of these variables corresponds to
+       * the text in 13.10
+       */
+      
+      JCOEF DC1, DC2, DC3;
+      JCOEF DC4, DC5, DC6;
+      JCOEF DC7, DC8, DC9;
+      
+      long       AC01, AC02;
+      long AC10, AC11;
+      long AC20;
+      
+      DC1 = above [col-1][0];
+      DC2 = above [col  ][0];
+      DC3 = above [col+1][0];
+      DC4 = currow[col-1][0];
+      DC5 = currow[col  ][0];
+      DC6 = currow[col+1][0];
+      DC7 = below [col-1][0];
+      DC8 = below [col  ][0];
+      DC9 = below [col+1][0];
+      
+#define DIVIDE_256(x)	x = ( (x) < 0 ? -((128-(x))/256) : ((x)+128)/256 )
+      
+      AC01 = (36 * (DC4 - DC6));
+      DIVIDE_256(AC01);
+      AC10 = (36 * (DC2 - DC8));
+      DIVIDE_256(AC10);
+      AC20 = (9 * (DC2 + DC8 - 2*DC5));
+      DIVIDE_256(AC20);
+      AC11 = (5 * ((DC1 - DC3) - (DC7 - DC9)));
+      DIVIDE_256(AC11);
+      AC02 = (9 * (DC4 + DC6 - 2*DC5));
+      DIVIDE_256(AC02);
+      
+      /* I think that this checks to see if the quantisation
+       * on the transmitting side would have produced this
+       * answer. If so, then we use our (hopefully better)
+       * estimate.
+       */
+
+#define ABS(x)	((x) < 0 ? -(x) : (x))
+
+#define COND_ASSIGN(_ac,_n,_z)   if ((ABS(output[col][_n] - (_ac))<<1) <= Qptr[_z]) output[col][_n] = (_ac)
+
+      COND_ASSIGN(AC01,  1, 1);
+      COND_ASSIGN(AC02,  2, 5);
+      COND_ASSIGN(AC10,  8, 2);
+      COND_ASSIGN(AC11,  9, 4);
+      COND_ASSIGN(AC20, 16, 3);
+    }
+  }
+}
+
+
+/*
+ * The method selection routine for cross-block smoothing.
+ */
+
+GLOBAL void
+jselbsmooth (decompress_info_ptr cinfo)
+{
+  /* just one implementation for now */
+  cinfo->methods->smooth_coefficients = smooth_coefficients;
+}
+
+#endif /* BLOCK_SMOOTHING_SUPPORTED */