--- /dev/null
+/*
+ * jdlossy.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 the control logic for the lossy JPEG decompressor.
+ */
+
+#define JPEG_INTERNALS
+#include "jinclude.h"
+#include "jpeglib.h"
+#include "jlossy.h"
+
+
+/*
+ * Compute output image dimensions and related values.
+ */
+
+METHODDEF(void)
+calc_output_dimensions (j_decompress_ptr cinfo)
+{
+#ifdef IDCT_SCALING_SUPPORTED
+ int ci;
+ jpeg_component_info *compptr;
+
+ /* Compute actual output image dimensions and DCT scaling choices. */
+ if (cinfo->scale_num * 8 <= cinfo->scale_denom) {
+ /* Provide 1/8 scaling */
+ cinfo->output_width = (JDIMENSION)
+ jdiv_round_up((long) cinfo->image_width, 8L);
+ cinfo->output_height = (JDIMENSION)
+ jdiv_round_up((long) cinfo->image_height, 8L);
+ cinfo->min_codec_data_unit = 1;
+ } else if (cinfo->scale_num * 4 <= cinfo->scale_denom) {
+ /* Provide 1/4 scaling */
+ cinfo->output_width = (JDIMENSION)
+ jdiv_round_up((long) cinfo->image_width, 4L);
+ cinfo->output_height = (JDIMENSION)
+ jdiv_round_up((long) cinfo->image_height, 4L);
+ cinfo->min_codec_data_unit = 2;
+ } else if (cinfo->scale_num * 2 <= cinfo->scale_denom) {
+ /* Provide 1/2 scaling */
+ cinfo->output_width = (JDIMENSION)
+ jdiv_round_up((long) cinfo->image_width, 2L);
+ cinfo->output_height = (JDIMENSION)
+ jdiv_round_up((long) cinfo->image_height, 2L);
+ cinfo->min_codec_data_unit = 4;
+ } else {
+ /* Provide 1/1 scaling */
+ cinfo->output_width = cinfo->image_width;
+ cinfo->output_height = cinfo->image_height;
+ cinfo->min_codec_data_unit = DCTSIZE;
+ }
+ /* In selecting the actual DCT scaling for each component, we try to
+ * scale up the chroma components via IDCT scaling rather than upsampling.
+ * This saves time if the upsampler gets to use 1:1 scaling.
+ * Note this code assumes that the supported DCT scalings are powers of 2.
+ */
+ for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
+ ci++, compptr++) {
+ int ssize = cinfo->min_codec_data_unit;
+ while (ssize < DCTSIZE &&
+ (compptr->h_samp_factor * ssize * 2 <=
+ cinfo->max_h_samp_factor * cinfo->min_codec_data_unit) &&
+ (compptr->v_samp_factor * ssize * 2 <=
+ cinfo->max_v_samp_factor * cinfo->min_codec_data_unit)) {
+ ssize = ssize * 2;
+ }
+ compptr->codec_data_unit = ssize;
+ }
+
+ /* Recompute downsampled dimensions of components;
+ * application needs to know these if using raw downsampled data.
+ */
+ for (ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
+ ci++, compptr++) {
+ /* Size in samples, after IDCT scaling */
+ compptr->downsampled_width = (JDIMENSION)
+ jdiv_round_up((long) cinfo->image_width *
+ (long) (compptr->h_samp_factor * compptr->codec_data_unit),
+ (long) (cinfo->max_h_samp_factor * DCTSIZE));
+ compptr->downsampled_height = (JDIMENSION)
+ jdiv_round_up((long) cinfo->image_height *
+ (long) (compptr->v_samp_factor * compptr->codec_data_unit),
+ (long) (cinfo->max_v_samp_factor * DCTSIZE));
+ }
+
+#else /* !IDCT_SCALING_SUPPORTED */
+
+ /* Hardwire it to "no scaling" */
+ cinfo->output_width = cinfo->image_width;
+ cinfo->output_height = cinfo->image_height;
+ /* jdinput.c has already initialized codec_data_unit to DCTSIZE,
+ * and has computed unscaled downsampled_width and downsampled_height.
+ */
+
+#endif /* IDCT_SCALING_SUPPORTED */
+}
+
+
+/*
+ * Save away a copy of the Q-table referenced by each component present
+ * in the current scan, unless already saved during a prior scan.
+ *
+ * In a multiple-scan JPEG file, the encoder could assign different components
+ * the same Q-table slot number, but change table definitions between scans
+ * so that each component uses a different Q-table. (The IJG encoder is not
+ * currently capable of doing this, but other encoders might.) Since we want
+ * to be able to dequantize all the components at the end of the file, this
+ * means that we have to save away the table actually used for each component.
+ * We do this by copying the table at the start of the first scan containing
+ * the component.
+ * The JPEG spec prohibits the encoder from changing the contents of a Q-table
+ * slot between scans of a component using that slot. If the encoder does so
+ * anyway, this decoder will simply use the Q-table values that were current
+ * at the start of the first scan for the component.
+ *
+ * The decompressor output side looks only at the saved quant tables,
+ * not at the current Q-table slots.
+ */
+
+LOCAL(void)
+latch_quant_tables (j_decompress_ptr cinfo)
+{
+ int ci, qtblno;
+ jpeg_component_info *compptr;
+ JQUANT_TBL * qtbl;
+
+ for (ci = 0; ci < cinfo->comps_in_scan; ci++) {
+ compptr = cinfo->cur_comp_info[ci];
+ /* No work if we already saved Q-table for this component */
+ if (compptr->quant_table != NULL)
+ continue;
+ /* Make sure specified quantization table is present */
+ qtblno = compptr->quant_tbl_no;
+ if (qtblno < 0 || qtblno >= NUM_QUANT_TBLS ||
+ cinfo->quant_tbl_ptrs[qtblno] == NULL)
+ ERREXIT1(cinfo, JERR_NO_QUANT_TABLE, qtblno);
+ /* OK, save away the quantization table */
+ qtbl = (JQUANT_TBL *)
+ (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_IMAGE,
+ SIZEOF(JQUANT_TBL));
+ MEMCOPY(qtbl, cinfo->quant_tbl_ptrs[qtblno], SIZEOF(JQUANT_TBL));
+ compptr->quant_table = qtbl;
+ }
+}
+
+
+/*
+ * Initialize for an input processing pass.
+ */
+
+METHODDEF(void)
+start_input_pass (j_decompress_ptr cinfo)
+{
+ j_lossy_d_ptr lossyd = (j_lossy_d_ptr) cinfo->codec;
+
+ latch_quant_tables(cinfo);
+ (*lossyd->entropy_start_pass) (cinfo);
+ (*lossyd->coef_start_input_pass) (cinfo);
+}
+
+
+/*
+ * Initialize for an output processing pass.
+ */
+
+METHODDEF(void)
+start_output_pass (j_decompress_ptr cinfo)
+{
+ j_lossy_d_ptr lossyd = (j_lossy_d_ptr) cinfo->codec;
+
+ (*lossyd->idct_start_pass) (cinfo);
+ (*lossyd->coef_start_output_pass) (cinfo);
+}
+
+/*
+ * Initialize the lossy decompression codec.
+ * This is called only once, during master selection.
+ */
+
+GLOBAL(void)
+jinit_lossy_d_codec (j_decompress_ptr cinfo)
+{
+ j_lossy_d_ptr lossyd;
+ boolean use_c_buffer;
+
+ /* Create subobject in permanent pool */
+ lossyd = (j_lossy_d_ptr)
+ (*cinfo->mem->alloc_small) ((j_common_ptr) cinfo, JPOOL_PERMANENT,
+ SIZEOF(jpeg_lossy_d_codec));
+ cinfo->codec = (struct jpeg_d_codec *) lossyd;
+
+ /* Initialize sub-modules */
+
+ /* Inverse DCT */
+ jinit_inverse_dct(cinfo);
+ /* Entropy decoding: either Huffman or arithmetic coding. */
+ if (cinfo->arith_code) {
+ jinit_arith_decoder(cinfo);
+ } else {
+ if (cinfo->process == JPROC_PROGRESSIVE) {
+#ifdef D_PROGRESSIVE_SUPPORTED
+ jinit_phuff_decoder(cinfo);
+#else
+ ERREXIT(cinfo, JERR_NOT_COMPILED);
+#endif
+ } else
+ jinit_shuff_decoder(cinfo);
+ }
+
+ use_c_buffer = cinfo->inputctl->has_multiple_scans || cinfo->buffered_image;
+ jinit_d_coef_controller(cinfo, use_c_buffer);
+
+ /* Initialize method pointers.
+ *
+ * Note: consume_data and decompress_data are assigned in jdcoefct.c.
+ */
+ lossyd->pub.calc_output_dimensions = calc_output_dimensions;
+ lossyd->pub.start_input_pass = start_input_pass;
+ lossyd->pub.start_output_pass = start_output_pass;
+}
+
+
+
+
git://git.creatis.insa-lyon.fr / gdcm.git / blobdiff