Use mozjpeg defaults by default

Since mozjpeg is now backward ABI-compatible with libjpeg[-turbo], it is now
possible to temporarily load mozjpeg into a binary application and cause that
application to generate uber-compressed JPEGs (at the expense of an extreme
performance loss, of course.)  For instance, someone could do

LD_LIBRARY_PATH=/opt/mozjpeg/lib convert blah_blah_blah

to make ImageMagick use mozjpeg instead of the system's pre-installed JPEG
library (libjpeg-turbo, in most cases.)  However, this only makes sense if
mozjpeg is actually producing different behavior by default than libjpeg-turbo.
Currently it isn't.  Currently it requires the application to set
JBOOLEAN_USE_MOZ_DEFAULTS to TRUE in order to enable the mozjpeg-specific
behavior, but of course applications that were built to use libjpeg[-turbo]
won't do that.  Thus, this patch sets use_moz_defaults to TRUE by default,
requiring an application to explicitly set it to FALSE in order to revert to
the libjpeg[-turbo] behavior (makes sense, since the only applications that
would need to revert to the libjpeg[-turbo] behavior would be mozjpeg-aware
applications.)

Note that we discussed the possibility of adding a function
(jpeg_revert_defaults()), which would act the same as jpeg_set_defaults() does
in libjpeg[-turbo].  This is a good solution for implementing the -revert
switch in cjpeg, but unfortunately it doesn't work for jpegtran.  The reason
is that jpeg_set_defaults() is called within the body of
jpeg_copy_critical_parameters(), which is part of the API.  So yet again,
if mozjpeg were loaded into a non-mozjpeg-aware application at run time, it
would be desirable for jpeg_copy_critical_parameters() to set the parameters
to mozjpeg defaults.  That means that, in order to implement the -revert
switch in jpegtran, it would be necessary to introduce a new function
(jpeg_revert_critical_parameters(), perhaps).  It seems cleaner to just keep
using the JBOOLEAN_USE_MOZ_DEFAULTS parameter to control the behavior of
jpeg_set_defaults(), even though this represents a minor abuse of the libjpeg
API (jpeg_set_defaults() is technically supposed to set all of the parameters
to defaults, irrespective of any previous state.  However, as long as we
document that JBOOLEAN_USE_MOZ_DEFAULTS works differently, then it should be
OK.)

cjpeg.c

@@ -634,8 +634,6 @@ main (int argc, char **argv)
    */
 
   cinfo.in_color_space = JCS_RGB; /* arbitrary guess */
-  if (jpeg_c_bool_param_supported(&cinfo, JBOOLEAN_USE_MOZ_DEFAULTS))
-    jpeg_c_set_bool_param(&cinfo, JBOOLEAN_USE_MOZ_DEFAULTS, TRUE);
   jpeg_set_defaults(&cinfo);
 
   /* Scan command line to find file names.

example.c

@@ -126,8 +126,6 @@ write_JPEG_file (char * filename, int quality)
   cinfo.image_height = image_height;
   cinfo.input_components = 3;           /* # of color components per pixel */
   cinfo.in_color_space = JCS_RGB;       /* colorspace of input image */
-  jpeg_c_set_bool_param(&cinfo, JBOOLEAN_USE_MOZ_DEFAULTS, TRUE); /* use Mozilla defaults for improved compression */
-  
   /* Now use the library's routine to set default compression parameters.
    * (You must set at least cinfo.in_color_space before calling this,
    * since the defaults depend on the source color space.)

jcapimin.c

@@ -99,6 +99,7 @@ jpeg_CreateCompress (j_compress_ptr cinfo, int version, size_t structsize)
   cinfo->master = (struct jpeg_comp_master *)
       jpeg_get_small ((j_common_ptr) cinfo, sizeof(struct jpeg_comp_master));
   MEMZERO(cinfo->master, sizeof(struct jpeg_comp_master));
+  cinfo->master->use_moz_defaults = TRUE;
 }
 
 

jcstest.c

@@ -1,7 +1,5 @@
 /*
  * Copyright (C)2011 D. R. Commander.  All Rights Reserved.
- * mozjpeg Modifications:
- * Copyright (C) 2014, Mozilla Corporation.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -87,8 +85,6 @@ int main(void)
 
   jpeg_create_compress(&cinfo);
   cinfo.input_components = 3;
-  if (jpeg_c_bool_param_supported(&cinfo, JBOOLEAN_USE_MOZ_DEFAULTS))
-    jpeg_c_set_bool_param(&cinfo, JBOOLEAN_USE_MOZ_DEFAULTS, TRUE);
   jpeg_set_defaults(&cinfo);
   cinfo.in_color_space = JCS_EXT_RGB;
   jpeg_default_colorspace(&cinfo);

jpegtran.c

@@ -415,8 +415,6 @@ main (int argc, char **argv)
   /* Initialize the JPEG compression object with default error handling. */
   dstinfo.err = jpeg_std_error(&jdsterr);
   jpeg_create_compress(&dstinfo);
-  if (jpeg_c_bool_param_supported(&dstinfo, JBOOLEAN_USE_MOZ_DEFAULTS))
-    jpeg_c_set_bool_param(&dstinfo, JBOOLEAN_USE_MOZ_DEFAULTS, TRUE);
 
   /* Scan command line to find file names.
    * It is convenient to use just one switch-parsing routine, but the switch

turbojpeg.c

@@ -206,7 +206,6 @@ static int setCompDefaults(struct jpeg_compress_struct *cinfo,
 	}
 
 	cinfo->input_components=tjPixelSize[pixelFormat];
-	cinfo->master->use_moz_defaults = TRUE;
 	jpeg_set_defaults(cinfo);
 
 	if((env=getenv("TJ_OPTIMIZE"))!=NULL && strlen(env)>0 && !strcmp(env, "1"))

yuvjpeg.c

@@ -217,9 +217,6 @@ int main(int argc, char *argv[]) {
 
   jpeg_stdio_dest(&cinfo, jpg_fd);
 
-  if (jpeg_c_bool_param_supported(&cinfo, JBOOLEAN_USE_MOZ_DEFAULTS))
-    jpeg_c_set_bool_param(&cinfo, JBOOLEAN_USE_MOZ_DEFAULTS, TRUE);
-
   cinfo.image_width = luma_width;
   cinfo.image_height = luma_height;
   cinfo.input_components = 3;