The Independent JPEG Group's JPEG software v1
diff --git a/jquant2.c b/jquant2.c
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+/*
+ * jquant2.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 2-pass color quantization (color mapping) routines.
+ * These routines are invoked via the methods color_quant_prescan,
+ * color_quant_doit, and color_quant_init/term.
+ */
+
+#include "jinclude.h"
+
+#ifdef QUANT_2PASS_SUPPORTED
+
+
+/*
+ * Initialize for two-pass color quantization.
+ */
+
+METHODDEF void
+color_quant_init (decompress_info_ptr cinfo)
+{
+ TRACEMS(cinfo->emethods, 1, "color_quant_init 2 pass");
+}
+
+
+/*
+ * Prescan some rows of pixels.
+ * Note: this could change the data being written into the big image array,
+ * if there were any benefit to doing so. The doit routine is not allowed
+ * to modify the big image array, because the memory manager is not required
+ * to support multiple write passes on a big image.
+ */
+
+METHODDEF void
+color_quant_prescan (decompress_info_ptr cinfo, int num_rows,
+ JSAMPIMAGE image_data)
+{
+ TRACEMS1(cinfo->emethods, 2, "color_quant_prescan %d rows", num_rows);
+}
+
+
+/*
+ * This routine makes the final pass over the image data.
+ * output_workspace is a one-component array of pixel dimensions at least
+ * as large as the input image strip; it can be used to hold the converted
+ * pixels' colormap indexes.
+ */
+
+METHODDEF void
+final_pass (decompress_info_ptr cinfo, int num_rows,
+ JSAMPIMAGE image_data, JSAMPARRAY output_workspace)
+{
+ TRACEMS1(cinfo->emethods, 2, "final_pass %d rows", num_rows);
+ /* for debug purposes, just emit input data */
+ /* NB: this only works for PPM output */
+ (*cinfo->methods->put_pixel_rows) (cinfo, num_rows, image_data);
+}
+
+
+/*
+ * Perform two-pass quantization: rescan the image data and output the
+ * converted data via put_color_map and put_pixel_rows.
+ * The source_method is a routine that can scan the image data; it can
+ * be called as many times as desired. The processing routine called by
+ * source_method has the same interface as color_quantize does in the
+ * one-pass case, except it must call put_pixel_rows itself. (This allows
+ * me to use multiple passes in which earlier passes don't output anything.)
+ */
+
+METHODDEF void
+color_quant_doit (decompress_info_ptr cinfo, quantize_caller_ptr source_method)
+{
+ TRACEMS(cinfo->emethods, 1, "color_quant_doit 2 pass");
+ (*source_method) (cinfo, final_pass);
+}
+
+
+/*
+ * Finish up at the end of the file.
+ */
+
+METHODDEF void
+color_quant_term (decompress_info_ptr cinfo)
+{
+ TRACEMS(cinfo->emethods, 1, "color_quant_term 2 pass");
+}
+
+
+/*
+ * Map some rows of pixels to the output colormapped representation.
+ * Not used in two-pass case.
+ */
+
+METHODDEF void
+color_quantize (decompress_info_ptr cinfo, int num_rows,
+ JSAMPIMAGE input_data, JSAMPARRAY output_data)
+{
+ ERREXIT(cinfo->emethods, "Should not get here!");
+}
+
+
+/*
+ * The method selection routine for 2-pass color quantization.
+ */
+
+GLOBAL void
+jsel2quantize (decompress_info_ptr cinfo)
+{
+ if (cinfo->two_pass_quantize) {
+ /* just one alternative for the moment */
+ cinfo->methods->color_quant_init = color_quant_init;
+ cinfo->methods->color_quant_prescan = color_quant_prescan;
+ cinfo->methods->color_quant_doit = color_quant_doit;
+ cinfo->methods->color_quant_term = color_quant_term;
+ cinfo->methods->color_quantize = color_quantize;
+ }
+}
+
+#endif /* QUANT_2PASS_SUPPORTED */