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Filter selection, palette index checks

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Palette index checking: checking on read was erroneously skipped.  pngcp can now
turn off the palette index checking or fix the errors (mainly to allow
comparison with libpng 1.6, which defaulted to ignoring it).  The API now
documents how the 'enabled' parameter works.  On read the check is on by default
(it was apparently off in libpng 1.6) however now if explicitly turned on the
warning message is stopped, this provides better interaction with
get_palette_max at the cost of a small API change (may need to be reviewed.)

Palette size errors: invalid entries in the palette are now set to #beaded to
make the errors more obvious and allow easy detection in memory.

Read transform pipeline caching: changes to fix the palette index check (which
are erroneously cached), the pipeline can now contain multiple caches.  E.g.
caching of packing of palette indices can be combined with caching of palette
RGB transforms.

Read code now checks for callbacks to read 0 data (and faults them).  Fixed the
reading of PNGs with multiple 0 length IDATs that failed as a result plus the
handling of zero length unknown.  (Which occurs, validly; the spurious warning
has been removed).

filter selection: the 1.6 and earlier sum of absolute differences algorithm has
been reintroduced with an option to disfavor some filters over others where the
sums are close (not yet exposed).  The selection code also logs the last known
occurence of each possible byte code across multiple lines.  This allows
detection of PNG images with lower bit depth than the format implies and,
therefore, allows the filtering to be turned off in those cases as well.

The default write zlib settings are still lower than libpng16.  The selection
algorithm is being refined (the overall results are worse than not doing any
filtering).

Signed-off-by: John Bowler <jbowler@acm.org>
This commit is contained in:
John Bowler
2016-05-15 16:32:01 -07:00
parent cf46e3748f
commit 5652acdd48
13 changed files with 298 additions and 98 deletions
Download Patch File Download Diff File Expand all files Collapse all files

122
pngtrans.c
View File

@@ -586,23 +586,35 @@ set_palette_max(png_structrp png_ptr, png_transformp tr, unsigned int max,
{
/* One of these must be true: */
# ifdef PNG_CHECK_FOR_INVALID_INDEX_SUPPORTED
if (max >= tr->args && !png_ptr->palette_index_check_issued)
if (max >= (tr->args & 0x1FFU) && !png_ptr->palette_index_check_issued)
{
# ifdef PNG_READ_SUPPORTED
/* In 1.7 only issue the error/warning by default; the 'check' API is
* used to enable/disable the check. Assume that if the app enabled it
* then the app will be checking the result with get_palette_max in
* read. In write an error results unless the check is disabled.
*/
if (png_ptr->palette_index_check == PNG_PALETTE_CHECK_DEFAULT
# ifdef PNG_WRITE_SUPPORTED
(png_ptr->read_struct ? png_chunk_benign_error : png_error)
# else /* !WRITE */
png_chunk_benign_error
# endif /* !WRITE */
# else /* !READ */
png_error
# endif /* !READ */
(png_ptr, "palette index too large");
|| (!png_ptr->read_struct &&
png_ptr->palette_index_check != PNG_PALETTE_CHECK_OFF)
# endif /* WRITE */
)
# ifdef PNG_READ_SUPPORTED
# ifdef PNG_WRITE_SUPPORTED
(png_ptr->read_struct ? png_chunk_benign_error : png_error)
# else /* !WRITE */
png_chunk_benign_error
# endif /* READ */
# else /* !READ */
png_error
# endif /* WRITE */
(png_ptr, "palette index too large");
png_ptr->palette_index_check_issued = 1;
}
# endif
# ifdef PNG_GET_PALETTE_MAX_SUPPORTED
png_ptr->palette_index_max = png_check_bits(png_ptr, max, 9);
png_ptr->palette_index_max = png_check_byte(png_ptr, max);
# endif
if (max == format_max)
@@ -642,7 +654,8 @@ palette_max_2bpp(png_transformp *tr, png_transform_controlp tc)
{
png_const_bytep sp = png_voidcast(png_const_bytep, tc->sp);
png_uint_32 width = tc->width;
unsigned int max = (*tr)->args; /* saved maximum */
const png_uint_32 args = (*tr)->args;
unsigned int max = args >> 24; /* saved maximum */
while (width > 0)
{
@@ -699,7 +712,7 @@ palette_max_2bpp(png_transformp *tr, png_transform_controlp tc)
}
/* End of input, check the next line. */
(*tr)->args = max;
(*tr)->args = (max << 24) + (args & 0xFFFFFFU);
}
static void
@@ -707,7 +720,8 @@ palette_max_4bpp(png_transformp *tr, png_transform_controlp tc)
{
png_const_bytep sp = png_voidcast(png_const_bytep, tc->sp);
png_uint_32 width = tc->width;
unsigned int max = (*tr)->args; /* saved maximum */
const png_uint_32 args = (*tr)->args;
unsigned int max = args >> 24; /* saved maximum */
while (width > 0)
{
@@ -725,12 +739,12 @@ palette_max_4bpp(png_transformp *tr, png_transform_controlp tc)
max = (input >> 4) & 0xFU;
}
if (max > (*tr)->args)
if (max > (args >> 24))
{
if (set_palette_max(tc->png_ptr, *tr, max, 15U))
return;
(*tr)->args = max;
(*tr)->args = (max << 24) + (args & 0xFFFFFFU);
}
}
@@ -739,7 +753,8 @@ palette_max_8bpp(png_transformp *tr, png_transform_controlp tc)
{
png_const_bytep sp = png_voidcast(png_const_bytep, tc->sp);
png_uint_32 width = tc->width;
unsigned int max = (*tr)->args; /* saved maximum */
const png_uint_32 args = (*tr)->args;
unsigned int max = args >> 24; /* saved maximum */
while (width > 0)
{
@@ -751,12 +766,12 @@ palette_max_8bpp(png_transformp *tr, png_transform_controlp tc)
--width;
}
if (max > (*tr)->args)
if (max > (args >> 24))
{
if (set_palette_max(tc->png_ptr, *tr, max, 255U))
return;
(*tr)->args = max;
(*tr)->args = (max << 24) + (args & 0xFFFFFFU);
}
}
@@ -764,26 +779,27 @@ static void
palette_max_init(png_transformp *tr, png_transform_controlp tc)
{
# define png_ptr (tc->png_ptr)
if ((tc->format & PNG_FORMAT_FLAG_COLORMAP) != 0)
affirm((tc->format & PNG_FORMAT_FLAG_COLORMAP) != 0);
debug(tc->init);
if (tc->init == PNG_TC_INIT_FINAL)
{
if (tc->init == PNG_TC_INIT_FINAL)
/* Record the palette depth to check here along with the running total
* in the top 8 bits (initially 0, which is always valid).
*/
(*tr)->args = png_ptr->num_palette;
switch (tc->bit_depth)
{
/* Record the palette depth to check here: */
(*tr)->args = png_ptr->num_palette;
switch (tc->bit_depth)
{
case 1: (*tr)->fn = palette_max_1bpp; break;
case 2: (*tr)->fn = palette_max_2bpp; break;
case 4: (*tr)->fn = palette_max_4bpp; break;
case 8: (*tr)->fn = palette_max_8bpp; break;
default:impossible("palette bit depth");
}
case 1: (*tr)->fn = palette_max_1bpp; break;
case 2: (*tr)->fn = palette_max_2bpp; break;
case 4: (*tr)->fn = palette_max_4bpp; break;
case 8: (*tr)->fn = palette_max_8bpp; break;
default:impossible("palette bit depth");
}
}
else
(*tr)->fn = NULL; /* not applicable */
png_ptr->palette_index_have_max = 1U;
}
# undef png_ptr
}
#endif /* PALETTE_MAX */
@@ -792,11 +808,7 @@ palette_max_init(png_transformp *tr, png_transform_controlp tc)
int PNGAPI
png_get_palette_max(png_const_structrp png_ptr, png_const_inforp info_ptr)
{
if (png_ptr != NULL
# ifdef PNG_CHECK_FOR_INVALID_INDEX_SUPPORTED
&& !png_ptr->palette_index_check_disabled
# endif
)
if (png_ptr != NULL && png_ptr->palette_index_have_max)
return png_ptr->palette_index_max;
/* This indicates to the caller that the information is not available: */
@@ -812,7 +824,7 @@ png_get_palette_max(png_const_structrp png_ptr, png_const_inforp info_ptr)
* fewer entries than the image's bit-depth would allow. We recover
* from this gracefully by filling any incomplete palette with zeros
* (opaque black). By default, when this occurs libpng will issue
* a benign error. This API can be used to override that behavior.
* an error. This API can be used to override that behavior.
*/
void PNGAPI
png_set_check_for_invalid_index(png_structrp png_ptr, int enabled)
@@ -821,17 +833,31 @@ png_set_check_for_invalid_index(png_structrp png_ptr, int enabled)
if (png_ptr != NULL)
{
if (png_ptr->read_struct)
{
# ifdef PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED
png_ptr->palette_index_check_disabled = enabled <= 0;
if (enabled > 0)
png_ptr->palette_index_check = PNG_PALETTE_CHECK_ON;
else if (enabled < 0)
png_ptr->palette_index_check = PNG_PALETTE_CHECK_OFF;
else
png_ptr->palette_index_check = PNG_PALETTE_CHECK_DEFAULT;
# else /* !READ_CHECK_FOR_INVALID_INDEX */
png_app_error(png_ptr, "no read palette check support");
# endif /* !READ_CHECK_FOR_INVALID_INDEX */
}
else /* write struct */
{
# ifdef PNG_WRITE_CHECK_FOR_INVALID_INDEX_SUPPORTED
png_ptr->palette_index_check_disabled = enabled <= 0;
if (enabled > 0)
png_ptr->palette_index_check = PNG_PALETTE_CHECK_ON;
else if (enabled < 0)
png_ptr->palette_index_check = PNG_PALETTE_CHECK_OFF;
else
png_ptr->palette_index_check = PNG_PALETTE_CHECK_DEFAULT;
# else /* !WRITE_CHECK_FOR_INVALID_INDEX */
png_app_error(png_ptr, "no write palette check support");
# endif /* !WRITE_CHECK_FOR_INVALID_INDEX */
}
}
}
#endif /* CHECK_FOR_INVALID_INDEX */
@@ -856,8 +882,11 @@ png_init_row_info(png_structrp png_ptr)
defined (PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED)
(png_ptr->read_struct
# ifdef PNG_READ_CHECK_FOR_INVALID_INDEX_SUPPORTED
&& !png_ptr->palette_index_check_disabled)
&& (png_ptr->palette_index_check == PNG_PALETTE_CHECK_ON ||
(png_ptr->palette_index_check == PNG_PALETTE_CHECK_DEFAULT
&& png_ptr->num_palette < (1U << png_ptr->bit_depth)))
# endif /* READ_CHECK_FOR_INVALID_INDEX */
)
# else /* no READ support */
0
# endif /* READ checks */
@@ -866,8 +895,11 @@ png_init_row_info(png_structrp png_ptr)
defined (PNG_WRITE_CHECK_FOR_INVALID_INDEX_SUPPORTED)
(!png_ptr->read_struct
# ifdef PNG_WRITE_CHECK_FOR_INVALID_INDEX_SUPPORTED
&& !png_ptr->palette_index_check_disabled)
&& (png_ptr->palette_index_check == PNG_PALETTE_CHECK_ON ||
(png_ptr->palette_index_check == PNG_PALETTE_CHECK_DEFAULT
&& png_ptr->num_palette < (1U << png_ptr->bit_depth)))
# endif /* WRITE_CHECK_FOR_INVALID_INDEX */
)
# else /* no WRITE support */
0
# endif /* WRITE checks */