The Independent JPEG Group's JPEG software v4a
diff --git a/jdcolor.c b/jdcolor.c
index fad9c73..f651c04 100644
--- a/jdcolor.c
+++ b/jdcolor.c
@@ -1,7 +1,7 @@
/*
* jdcolor.c
*
- * Copyright (C) 1991, 1992, Thomas G. Lane.
+ * Copyright (C) 1991, 1992, 1993, 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.
*
@@ -223,6 +223,8 @@
GLOBAL void
jseldcolor (decompress_info_ptr cinfo)
{
+ int ci;
+
/* Make sure num_components agrees with jpeg_color_space */
switch (cinfo->jpeg_color_space) {
case CS_GRAYSCALE:
@@ -247,7 +249,10 @@
break;
}
- /* Set color_out_comps and conversion method based on requested space */
+ /* Set color_out_comps and conversion method based on requested space. */
+ /* Also clear the component_needed flags for any unused components, */
+ /* so that earlier pipeline stages can avoid useless computation. */
+
switch (cinfo->out_color_space) {
case CS_GRAYSCALE:
cinfo->color_out_comps = 1;
@@ -257,6 +262,9 @@
cinfo->methods->color_convert = grayscale_convert;
cinfo->methods->colorout_init = null_init;
cinfo->methods->colorout_term = null_term;
+ /* For color->grayscale conversion, only the Y (0) component is needed */
+ for (ci = 1; ci < cinfo->num_components; ci++)
+ cinfo->cur_comp_info[ci]->component_needed = FALSE;
} else
ERREXIT(cinfo->emethods, "Unsupported color conversion request");
break;
