The Independent JPEG Group's JPEG software v1

jdmaster.c

@@ -0,0 +1,180 @@
+/*
+ * jdmaster.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 the main control for the JPEG decompressor.
+ * The system-dependent (user interface) code should call jpeg_decompress()
+ * after doing appropriate setup of the decompress_info_struct parameter.
+ */
+
+#include "jinclude.h"
+
+
+METHODDEF void
+d_per_scan_method_selection (decompress_info_ptr cinfo)
+/* Central point for per-scan method selection */
+{
+  /* MCU disassembly */
+  jseldmcu(cinfo);
+  /* Un-subsampling of pixels */
+  jselunsubsample(cinfo);
+}
+
+
+LOCAL void
+d_initial_method_selection (decompress_info_ptr cinfo)
+/* Central point for initial method selection (after reading file header) */
+{
+  /* JPEG file scanning method selection is already done. */
+  /* So is output file format selection (both are done by user interface). */
+
+  /* Entropy decoding: either Huffman or arithmetic coding. */
+#ifdef ARITH_CODING_SUPPORTED
+  jseldarithmetic(cinfo);
+#else
+  if (cinfo->arith_code) {
+    ERREXIT(cinfo->emethods, "Arithmetic coding not supported");
+  }
+#endif
+  jseldhuffman(cinfo);
+  /* Cross-block smoothing */
+#ifdef BLOCK_SMOOTHING_SUPPORTED
+  jselbsmooth(cinfo);
+#else
+  cinfo->do_block_smoothing = FALSE;
+#endif
+  /* Gamma and color space conversion */
+  jseldcolor(cinfo);
+
+  /* Color quantization */
+#ifdef QUANT_1PASS_SUPPORTED
+#ifndef QUANT_2PASS_SUPPORTED
+  cinfo->two_pass_quantize = FALSE; /* only have 1-pass */
+#endif
+#else /* not QUANT_1PASS_SUPPORTED */
+#ifdef QUANT_2PASS_SUPPORTED
+  cinfo->two_pass_quantize = TRUE; /* only have 2-pass */
+#else /* not QUANT_2PASS_SUPPORTED */
+  if (cinfo->quantize_colors) {
+    ERREXIT(cinfo->emethods, "Color quantization was not compiled");
+  }
+#endif
+#endif
+
+#ifdef QUANT_1PASS_SUPPORTED
+  jsel1quantize(cinfo);
+#endif
+#ifdef QUANT_2PASS_SUPPORTED
+  jsel2quantize(cinfo);
+#endif
+
+  /* Pipeline control */
+  jseldpipeline(cinfo);
+  /* Overall control (that's me!) */
+  cinfo->methods->d_per_scan_method_selection = d_per_scan_method_selection;
+}
+
+
+LOCAL void
+initial_setup (decompress_info_ptr cinfo)
+/* Do computations that are needed before initial method selection */
+{
+  short ci;
+  jpeg_component_info *compptr;
+
+  /* Compute maximum sampling factors; check factor validity */
+  cinfo->max_h_samp_factor = 1;
+  cinfo->max_v_samp_factor = 1;
+  for (ci = 0; ci < cinfo->num_components; ci++) {
+    compptr = &cinfo->comp_info[ci];
+    if (compptr->h_samp_factor<=0 || compptr->h_samp_factor>MAX_SAMP_FACTOR ||
+	compptr->v_samp_factor<=0 || compptr->v_samp_factor>MAX_SAMP_FACTOR)
+      ERREXIT(cinfo->emethods, "Bogus sampling factors");
+    cinfo->max_h_samp_factor = MAX(cinfo->max_h_samp_factor,
+				   compptr->h_samp_factor);
+    cinfo->max_v_samp_factor = MAX(cinfo->max_v_samp_factor,
+				   compptr->v_samp_factor);
+
+  }
+
+  /* Compute logical subsampled dimensions of components */
+  for (ci = 0; ci < cinfo->num_components; ci++) {
+    compptr = &cinfo->comp_info[ci];
+    compptr->true_comp_width = (cinfo->image_width * compptr->h_samp_factor
+				+ cinfo->max_h_samp_factor - 1)
+				/ cinfo->max_h_samp_factor;
+    compptr->true_comp_height = (cinfo->image_height * compptr->v_samp_factor
+				 + cinfo->max_v_samp_factor - 1)
+				 / cinfo->max_v_samp_factor;
+  }
+}
+
+
+/*
+ * This is the main entry point to the JPEG decompressor.
+ */
+
+
+GLOBAL void
+jpeg_decompress (decompress_info_ptr cinfo)
+{
+  short i;
+
+  /* Initialize pointers as needed to mark stuff unallocated. */
+  cinfo->comp_info = NULL;
+  for (i = 0; i < NUM_QUANT_TBLS; i++)
+    cinfo->quant_tbl_ptrs[i] = NULL;
+  for (i = 0; i < NUM_HUFF_TBLS; i++) {
+    cinfo->dc_huff_tbl_ptrs[i] = NULL;
+    cinfo->ac_huff_tbl_ptrs[i] = NULL;
+  }
+
+  /* Read the JPEG file header markers; everything up through the first SOS
+   * marker is read now.  NOTE: the user interface must have initialized the
+   * read_file_header method pointer (eg, by calling jselrjfif or jselrtiff).
+   * The other file reading methods (read_scan_header etc.) were probably
+   * set at the same time, but could be set up by read_file_header itself.
+   */
+  (*cinfo->methods->read_file_header) (cinfo);
+  if (! ((*cinfo->methods->read_scan_header) (cinfo)))
+    ERREXIT(cinfo->emethods, "Empty JPEG file");
+
+  /* Give UI a chance to adjust decompression parameters and select */
+  /* output file format based on info from file header. */
+  (*cinfo->methods->d_ui_method_selection) (cinfo);
+
+  /* Now select methods for decompression steps. */
+  initial_setup(cinfo);
+  d_initial_method_selection(cinfo);
+
+  /* Initialize the output file & other modules as needed */
+  /* (color_quant and entropy_decoder are inited by pipeline controller) */
+
+  (*cinfo->methods->output_init) (cinfo);
+  (*cinfo->methods->colorout_init) (cinfo);
+
+  /* And let the pipeline controller do the rest. */
+  (*cinfo->methods->d_pipeline_controller) (cinfo);
+
+  /* Finish output file, release working storage, etc */
+  (*cinfo->methods->colorout_term) (cinfo);
+  (*cinfo->methods->output_term) (cinfo);
+  (*cinfo->methods->read_file_trailer) (cinfo);
+
+  /* Release allocated storage for tables */
+#define FREE(ptr)  if ((ptr) != NULL) \
+			(*cinfo->emethods->free_small) ((void *) ptr)
+
+  FREE(cinfo->comp_info);
+  for (i = 0; i < NUM_QUANT_TBLS; i++)
+    FREE(cinfo->quant_tbl_ptrs[i]);
+  for (i = 0; i < NUM_HUFF_TBLS; i++) {
+    FREE(cinfo->dc_huff_tbl_ptrs[i]);
+    FREE(cinfo->ac_huff_tbl_ptrs[i]);
+  }
+
+  /* My, that was easy, wasn't it? */
+}