From eb84b2179b059aef3a0ceb5fc9a8b66b9de81234 Mon Sep 17 00:00:00 2001
From: Socks the Fox <jade@socksthefox.net>
Date: Mon, 18 Jan 2016 10:42:41 -0600
Subject: [PATCH] Initial 16 bit per channel PNG support
---
stb_image.h | 133 ++++++++++++++++++++++++++++++++++++++++++++--------
1 file changed, 113 insertions(+), 20 deletions(-)
diff --git a/stb_image.h b/stb_image.h
index be25097..daa47ae 100644
--- a/stb_image.h
+++ b/stb_image.h
@@ -3938,6 +3938,7 @@ typedef struct
{
stbi__context *s;
stbi_uc *idata, *expanded, *out;
+ int depth;
} stbi__png;
@@ -3977,14 +3978,19 @@ static stbi_uc stbi__depth_scale_table[9] = { 0, 0xff, 0x55, 0, 0x11, 0,0,0, 0x0
// create the png data from post-deflated data
static int stbi__create_png_image_raw(stbi__png *a, stbi_uc *raw, stbi__uint32 raw_len, int out_n, stbi__uint32 x, stbi__uint32 y, int depth, int color)
{
+ int bytes = (depth == 16? 2 : 1);
stbi__context *s = a->s;
- stbi__uint32 i,j,stride = x*out_n;
+ stbi__uint32 i,j,stride = x*out_n*bytes;
stbi__uint32 img_len, img_width_bytes;
int k;
int img_n = s->img_n; // copy it into a local for later
+ int output_bytes = out_n*bytes;
+ int filter_bytes = img_n*bytes;
+ int width = x;
+
STBI_ASSERT(out_n == s->img_n || out_n == s->img_n+1);
- a->out = (stbi_uc *) stbi__malloc(x * y * out_n); // extra bytes to write off the end into
+ a->out = (stbi_uc *) stbi__malloc(x * y * output_bytes); // extra bytes to write off the end into
if (!a->out) return stbi__err("outofmem", "Out of memory");
img_width_bytes = (((img_n * x * depth) + 7) >> 3);
@@ -3999,8 +4005,7 @@ static int stbi__create_png_image_raw(stbi__png *a, stbi_uc *raw, stbi__uint32 r
stbi_uc *cur = a->out + stride*j;
stbi_uc *prior = cur - stride;
int filter = *raw++;
- int filter_bytes = img_n;
- int width = x;
+
if (filter > 4)
return stbi__err("invalid filter","Corrupt PNG");
@@ -4033,6 +4038,14 @@ static int stbi__create_png_image_raw(stbi__png *a, stbi_uc *raw, stbi__uint32 r
raw += img_n;
cur += out_n;
prior += out_n;
+ } else if (depth == 16) {
+ if (img_n != out_n) {
+ cur[filter_bytes] = 255; // first pixel top byte
+ cur[filter_bytes+1] = 255; // first pixel bottom byte
+ }
+ raw += filter_bytes;
+ cur += output_bytes;
+ prior += output_bytes;
} else {
raw += 1;
cur += 1;
@@ -4041,7 +4054,7 @@ static int stbi__create_png_image_raw(stbi__png *a, stbi_uc *raw, stbi__uint32 r
// this is a little gross, so that we don't switch per-pixel or per-component
if (depth < 8 || img_n == out_n) {
- int nk = (width - 1)*img_n;
+ int nk = (width - 1)*filter_bytes;
#define CASE(f) \
case f: \
for (k=0; k < nk; ++k)
@@ -4061,18 +4074,27 @@ static int stbi__create_png_image_raw(stbi__png *a, stbi_uc *raw, stbi__uint32 r
STBI_ASSERT(img_n+1 == out_n);
#define CASE(f) \
case f: \
- for (i=x-1; i >= 1; --i, cur[img_n]=255,raw+=img_n,cur+=out_n,prior+=out_n) \
- for (k=0; k < img_n; ++k)
+ for (i=x-1; i >= 1; --i, cur[filter_bytes]=255,raw+=filter_bytes,cur+=output_bytes,prior+=output_bytes) \
+ for (k=0; k < filter_bytes; ++k)
switch (filter) {
CASE(STBI__F_none) cur[k] = raw[k]; break;
- CASE(STBI__F_sub) cur[k] = STBI__BYTECAST(raw[k] + cur[k-out_n]); break;
+ CASE(STBI__F_sub) cur[k] = STBI__BYTECAST(raw[k] + cur[k- output_bytes]); break;
CASE(STBI__F_up) cur[k] = STBI__BYTECAST(raw[k] + prior[k]); break;
- CASE(STBI__F_avg) cur[k] = STBI__BYTECAST(raw[k] + ((prior[k] + cur[k-out_n])>>1)); break;
- CASE(STBI__F_paeth) cur[k] = STBI__BYTECAST(raw[k] + stbi__paeth(cur[k-out_n],prior[k],prior[k-out_n])); break;
- CASE(STBI__F_avg_first) cur[k] = STBI__BYTECAST(raw[k] + (cur[k-out_n] >> 1)); break;
- CASE(STBI__F_paeth_first) cur[k] = STBI__BYTECAST(raw[k] + stbi__paeth(cur[k-out_n],0,0)); break;
+ CASE(STBI__F_avg) cur[k] = STBI__BYTECAST(raw[k] + ((prior[k] + cur[k- output_bytes])>>1)); break;
+ CASE(STBI__F_paeth) cur[k] = STBI__BYTECAST(raw[k] + stbi__paeth(cur[k- output_bytes],prior[k],prior[k- output_bytes])); break;
+ CASE(STBI__F_avg_first) cur[k] = STBI__BYTECAST(raw[k] + (cur[k- output_bytes] >> 1)); break;
+ CASE(STBI__F_paeth_first) cur[k] = STBI__BYTECAST(raw[k] + stbi__paeth(cur[k- output_bytes],0,0)); break;
}
#undef CASE
+
+ // the loop above sets the high byte of the pixels' alpha, but for
+ // 16 bit png files we also need the low byte set. we'll do that here.
+ if (depth == 16) {
+ cur = a->out + stride*j; // start at the beginning of the row again
+ for (i=0; i < x; ++i,cur+=output_bytes) {
+ cur[filter_bytes+1] = 255;
+ }
+ }
}
}
@@ -4148,6 +4170,17 @@ static int stbi__create_png_image_raw(stbi__png *a, stbi_uc *raw, stbi__uint32 r
}
}
}
+ } else if (depth == 16) {
+ // force the image data from big-endian to platform-native.
+ // this is done in a separate pass due to the decoding relying
+ // on the data being untouched, but could probably be done
+ // per-line during decode if care is taken.
+ stbi_uc *cur = a->out;
+ stbi__uint16 *cur16 = (stbi__uint16*)cur;
+
+ for(i=0; i < x*y*out_n; ++i,cur16++,cur+=2) {
+ *cur16 = (cur[0] << 8) | cur[1];
+ }
}
return 1;
@@ -4220,6 +4253,31 @@ static int stbi__compute_transparency(stbi__png *z, stbi_uc tc[3], int out_n)
return 1;
}
+static int stbi__compute_transparency16(stbi__png *z, stbi__uint16 tc[3], int out_n)
+{
+ stbi__context *s = z->s;
+ stbi__uint32 i, pixel_count = s->img_x * s->img_y;
+ stbi__uint16 *p = (stbi__uint16*) z->out;
+
+ // compute color-based transparency, assuming we've
+ // already got 65535 as the alpha value in the output
+ STBI_ASSERT(out_n == 2 || out_n == 4);
+
+ if (out_n == 2) {
+ for (i = 0; i < pixel_count; ++i) {
+ p[1] = (p[0] == tc[0] ? 0 : 65535);
+ p += 2;
+ }
+ } else {
+ for (i = 0; i < pixel_count; ++i) {
+ if (p[0] == tc[0] && p[1] == tc[1] && p[2] == tc[2])
+ p[3] = 0;
+ p += 4;
+ }
+ }
+ return 1;
+}
+
static int stbi__expand_png_palette(stbi__png *a, stbi_uc *palette, int len, int pal_img_n)
{
stbi__uint32 i, pixel_count = a->s->img_x * a->s->img_y;
@@ -4257,6 +4315,26 @@ static int stbi__expand_png_palette(stbi__png *a, stbi_uc *palette, int len, int
return 1;
}
+static int stbi__reduce_png(stbi__png *p)
+{
+ int i;
+ int img_len = p->s->img_x * p->s->img_y * p->s->img_out_n;
+ stbi_uc *reduced;
+ stbi__uint16 *orig = (stbi__uint16*)p->out;
+
+ if (p->depth != 16) return 1; // don't need to do anything if not 16-bit data
+
+ reduced = (stbi_uc *)stbi__malloc(img_len);
+ if (p == NULL) return stbi__err("outofmem", "Out of memory");
+
+ for (i = 0; i < img_len; ++i) reduced[i] = (stbi_uc)((orig[i] >> 8) & 0xFF); // top half of each byte is a decent approx of 16->8 bit scaling
+
+ p->out = reduced;
+ STBI_FREE(orig);
+
+ return 1;
+}
+
static int stbi__unpremultiply_on_load = 0;
static int stbi__de_iphone_flag = 0;
@@ -4318,8 +4396,9 @@ static int stbi__parse_png_file(stbi__png *z, int scan, int req_comp)
{
stbi_uc palette[1024], pal_img_n=0;
stbi_uc has_trans=0, tc[3];
+ stbi__uint16 tc16[3];
stbi__uint32 ioff=0, idata_limit=0, i, pal_len=0;
- int first=1,k,interlace=0, color=0, depth=0, is_iphone=0;
+ int first=1,k,interlace=0, color=0, is_iphone=0;
stbi__context *s = z->s;
z->expanded = NULL;
@@ -4344,8 +4423,9 @@ static int stbi__parse_png_file(stbi__png *z, int scan, int req_comp)
if (c.length != 13) return stbi__err("bad IHDR len","Corrupt PNG");
s->img_x = stbi__get32be(s); if (s->img_x > (1 << 24)) return stbi__err("too large","Very large image (corrupt?)");
s->img_y = stbi__get32be(s); if (s->img_y > (1 << 24)) return stbi__err("too large","Very large image (corrupt?)");
- depth = stbi__get8(s); if (depth != 1 && depth != 2 && depth != 4 && depth != 8) return stbi__err("1/2/4/8-bit only","PNG not supported: 1/2/4/8-bit only");
+ z->depth = stbi__get8(s); if (z->depth != 1 && z->depth != 2 && z->depth != 4 && z->depth != 8 && z->depth != 16) return stbi__err("1/2/4/8/16-bit only","PNG not supported: 1/2/4/8/16-bit only");
color = stbi__get8(s); if (color > 6) return stbi__err("bad ctype","Corrupt PNG");
+ if (color == 3 && z->depth == 16) return stbi__err("bad ctype","Corrupt PNG");
if (color == 3) pal_img_n = 3; else if (color & 1) return stbi__err("bad ctype","Corrupt PNG");
comp = stbi__get8(s); if (comp) return stbi__err("bad comp method","Corrupt PNG");
filter= stbi__get8(s); if (filter) return stbi__err("bad filter method","Corrupt PNG");
@@ -4393,8 +4473,11 @@ static int stbi__parse_png_file(stbi__png *z, int scan, int req_comp)
if (!(s->img_n & 1)) return stbi__err("tRNS with alpha","Corrupt PNG");
if (c.length != (stbi__uint32) s->img_n*2) return stbi__err("bad tRNS len","Corrupt PNG");
has_trans = 1;
- for (k=0; k < s->img_n; ++k)
- tc[k] = (stbi_uc) (stbi__get16be(s) & 255) * stbi__depth_scale_table[depth]; // non 8-bit images will be larger
+ if (z->depth == 16) {
+ for (k = 0; k < s->img_n; ++k) tc16[k] = stbi__get16be(s); // copy the values as-is
+ } else {
+ for (k = 0; k < s->img_n; ++k) tc[k] = (stbi_uc)(stbi__get16be(s) & 255) * stbi__depth_scale_table[z->depth]; // non 8-bit images will be larger
+ }
}
break;
}
@@ -4424,7 +4507,7 @@ static int stbi__parse_png_file(stbi__png *z, int scan, int req_comp)
if (scan != STBI__SCAN_load) return 1;
if (z->idata == NULL) return stbi__err("no IDAT","Corrupt PNG");
// initial guess for decoded data size to avoid unnecessary reallocs
- bpl = (s->img_x * depth + 7) / 8; // bytes per line, per component
+ bpl = (s->img_x * z->depth + 7) / 8; // bytes per line, per component
raw_len = bpl * s->img_y * s->img_n /* pixels */ + s->img_y /* filter mode per row */;
z->expanded = (stbi_uc *) stbi_zlib_decode_malloc_guesssize_headerflag((char *) z->idata, ioff, raw_len, (int *) &raw_len, !is_iphone);
if (z->expanded == NULL) return 0; // zlib should set error
@@ -4433,9 +4516,14 @@ static int stbi__parse_png_file(stbi__png *z, int scan, int req_comp)
s->img_out_n = s->img_n+1;
else
s->img_out_n = s->img_n;
- if (!stbi__create_png_image(z, z->expanded, raw_len, s->img_out_n, depth, color, interlace)) return 0;
- if (has_trans)
- if (!stbi__compute_transparency(z, tc, s->img_out_n)) return 0;
+ if (!stbi__create_png_image(z, z->expanded, raw_len, s->img_out_n, z->depth, color, interlace)) return 0;
+ if (has_trans) {
+ if (z->depth == 16) {
+ if (!stbi__compute_transparency16(z, tc16, s->img_out_n)) return 0;
+ } else {
+ if (!stbi__compute_transparency(z, tc, s->img_out_n)) return 0;
+ }
+ }
if (is_iphone && stbi__de_iphone_flag && s->img_out_n > 2)
stbi__de_iphone(z);
if (pal_img_n) {
@@ -4477,6 +4565,11 @@ static unsigned char *stbi__do_png(stbi__png *p, int *x, int *y, int *n, int req
unsigned char *result=NULL;
if (req_comp < 0 || req_comp > 4) return stbi__errpuc("bad req_comp", "Internal error");
if (stbi__parse_png_file(p, STBI__SCAN_load, req_comp)) {
+ if (p->depth == 16) {
+ if (!stbi__reduce_png(p)) {
+ return result;
+ }
+ }
result = p->out;
p->out = NULL;
if (req_comp && req_comp != p->s->img_out_n) {