Partial revert BPC related check of #975 (#979)

PR #975 introduced a check that rejects images that have different bit depth/sign
per compoment in SIZ marker if the JP2 IHDR box has BPC != 255
This didn't work properly if decoding a .j2k file since the new bit added in
opj_cp_t wasn't initialized to the right value.
For clarity, tThis new bit has also been renamed to allow_different_bit_depth_sign

But looking closer at the code, it seems we were already tolerant to inconsistencies.
For example we parsed a JP2 BPCC box even if BPC != 255 (just a warning is emitted)
So failing hard in opj_j2k_read_siz() wouldn't be very inconsistent, and that
alone cannot protect against other issues, so just emit a warning if BPC != 255
and the SIZ marker contains different bit depth/sign per component.

Note: we could also check that the content of JP2 BPCC box is consistant with the one
of the SIZ marker.

3 files changed, 10 insertions, 6 deletions

diff --git a/src/lib/openjp2/j2k.c b/src/lib/openjp2/j2k.c
index 5a169e18..9cdc770b 100644
--- a/src/lib/openjp2/j2k.c
+++ b/src/lib/openjp2/j2k.c
@@ -2239,14 +2239,14 @@ static OPJ_BOOL opj_j2k_read_siz(opj_j2k_t *p_j2k,
             if (i == 0) {
                 l_prec0 = l_img_comp->prec;
                 l_sgnd0 = l_img_comp->sgnd;
-            } else if (l_cp->bpc_is_255 == 0
+            } else if (!l_cp->allow_different_bit_depth_sign
                        && (l_img_comp->prec != l_prec0 || l_img_comp->sgnd != l_sgnd0)) {
-                opj_event_msg(p_manager, EVT_ERROR,
-                              "Invalid precision and/or sgnd values for comp[%d]:\n"
+                opj_event_msg(p_manager, EVT_WARNING,
+                              "Despite JP2 BPC!=255, precision and/or sgnd values for comp[%d] is different than comp[0]:\n"
                               "        [0] prec(%d) sgnd(%d) [%d] prec(%d) sgnd(%d)\n", i, l_prec0, l_sgnd0,
                               i, l_img_comp->prec, l_img_comp->sgnd);
-                return OPJ_FALSE;
             }
+            /* TODO: we should perhaps also check against JP2 BPCC values */
         }
         opj_read_bytes(p_header_data, &tmp, 1); /* XRsiz_i */
         ++p_header_data;
@@ -9273,6 +9273,9 @@ opj_j2k_t* opj_j2k_create_decompress(void)
 
     l_j2k->m_is_decoder = 1;
     l_j2k->m_cp.m_is_decoder = 1;
+    /* in the absence of JP2 boxes, consider different bit depth / sign */
+    /* per component is allowed */
+    l_j2k->m_cp.allow_different_bit_depth_sign = 1;
 
 #ifdef OPJ_DISABLE_TPSOT_FIX
     l_j2k->m_specific_param.m_decoder.m_nb_tile_parts_correction_checked = 1;
diff --git a/src/lib/openjp2/j2k.h b/src/lib/openjp2/j2k.h
index eeef6a9e..d61c96db 100644
--- a/src/lib/openjp2/j2k.h
+++ b/src/lib/openjp2/j2k.h
@@ -446,7 +446,8 @@ typedef struct opj_cp {
     OPJ_BITFIELD ppm : 1;
     /** tells if the parameter is a coding or decoding one */
     OPJ_BITFIELD m_is_decoder : 1;
-    OPJ_BITFIELD bpc_is_255 : 1;
+    /** whether different bit depth or sign per component is allowed. Decoder only for ow */
+    OPJ_BITFIELD allow_different_bit_depth_sign : 1;
     /* <<UniPG */
 } opj_cp_t;
 
diff --git a/src/lib/openjp2/jp2.c b/src/lib/openjp2/jp2.c
index df35a164..f3ccb997 100644
--- a/src/lib/openjp2/jp2.c
+++ b/src/lib/openjp2/jp2.c
@@ -619,7 +619,7 @@ static OPJ_BOOL opj_jp2_read_ihdr(opj_jp2_t *jp2,
     opj_read_bytes(p_image_header_data, &(jp2->IPR), 1);        /* IPR */
     ++ p_image_header_data;
 
-    jp2->j2k->m_cp.bpc_is_255 = (jp2->bpc == 255);
+    jp2->j2k->m_cp.allow_different_bit_depth_sign = (jp2->bpc == 255);
     jp2->j2k->ihdr_w = jp2->w;
     jp2->j2k->ihdr_h = jp2->h;
     jp2->has_ihdr = 1;