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Allow decoding of any grayscale png as any of the grayscale destination formats #278

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Allow decoding of any grayscale png as any of the grayscale destination formats #278

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149 changes: 83 additions & 66 deletions spng/spng.c
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Original file line number Diff line number Diff line change
Expand Up @@ -640,10 +640,14 @@ static int check_decode_fmt(const struct spng_ihdr *ihdr, const int fmt)
return 0;
case SPNG_FMT_G8:
case SPNG_FMT_GA8:
if(ihdr->color_type == SPNG_COLOR_TYPE_GRAYSCALE && ihdr->bit_depth <= 8) return 0;
if(ihdr->color_type == SPNG_COLOR_TYPE_GRAYSCALE ||
ihdr->color_type == SPNG_COLOR_TYPE_GRAYSCALE_ALPHA)
return 0;
else return SPNG_EFMT;
case SPNG_FMT_GA16:
if(ihdr->color_type == SPNG_COLOR_TYPE_GRAYSCALE && ihdr->bit_depth == 16) return 0;
if(ihdr->color_type == SPNG_COLOR_TYPE_GRAYSCALE ||
ihdr->color_type == SPNG_COLOR_TYPE_GRAYSCALE_ALPHA)
return 0;
else return SPNG_EFMT;
default: return SPNG_EFMT;
}
Expand Down Expand Up @@ -1780,6 +1784,36 @@ static inline void gamma_correct_row(unsigned char *row, uint32_t pixels, int fm
px[2] = gamma_lut[px[2]];
}
}
else if(fmt == SPNG_FMT_G8)
{
unsigned char *px;
for(i=0; i < pixels; i++)
{
px = row + i;
px[0] = gamma_lut[px[0]];
}
}
else if(fmt == SPNG_FMT_GA8)
{
unsigned char *px;
for(i=0; i < pixels; i++)
{
px = row + i * 2;
px[0] = gamma_lut[px[0]];
}
}
else if(fmt == SPNG_FMT_GA16)
{
for(i=0; i < pixels; i++)
{
uint16_t px[2];
memcpy(&px, row + i * 4, 4);

px[0] = gamma_lut[px[0]];

memcpy(row + i * 4, px, 4);
}
}
}

/* Apply transparency to output row */
Expand Down Expand Up @@ -1922,6 +1956,19 @@ static inline void scale_row(unsigned char *row, uint32_t pixels, int fmt, unsig
row[i*2] = sample_to_target(row[i*2], depth, sbit->grayscale_bits, 8);
}
}
else if(fmt == SPNG_FMT_GA16)
{
uint16_t px[2];
for(i=0; i < pixels; i++)
{
memcpy(px, row + i * 4, 4);

px[0] = sample_to_target(px[0], depth, sbit->grayscale_bits, 16);
px[1] = sample_to_target(px[1], depth, sbit->alpha_bits, 16);

memcpy(row + i * 4, px, 4);
}
}
}

/* Expand to *row using 8-bit palette indices from *scanline */
Expand Down Expand Up @@ -1979,54 +2026,6 @@ static void expand_row(unsigned char *row,
}
}

/* Unpack 1/2/4/8-bit samples to G8/GA8/GA16 or G16 -> GA16 */
static void unpack_scanline(unsigned char *out, const unsigned char *scanline, uint32_t width, unsigned bit_depth, int fmt)
{
struct spng__iter iter = spng__iter_init(bit_depth, scanline);
uint32_t i;
uint16_t sample, alpha = 65535;


if(fmt == SPNG_FMT_GA8) goto ga8;
else if(fmt == SPNG_FMT_GA16) goto ga16;

/* 1/2/4-bit -> 8-bit */
for(i=0; i < width; i++) out[i] = get_sample(&iter);

return;

ga8:
/* 1/2/4/8-bit -> GA8 */
for(i=0; i < width; i++)
{
out[i*2] = get_sample(&iter);
out[i*2 + 1] = 255;
}

return;

ga16:

/* 16 -> GA16 */
if(bit_depth == 16)
{
for(i=0; i < width; i++)
{
memcpy(out + i * 4, scanline + i * 2, 2);
memcpy(out + i * 4 + 2, &alpha, 2);
}
return;
}

/* 1/2/4/8-bit -> GA16 */
for(i=0; i < width; i++)
{
sample = get_sample(&iter);
memcpy(out + i * 4, &sample, 2);
memcpy(out + i * 4 + 2, &alpha, 2);
}
}

static int check_ihdr(const struct spng_ihdr *ihdr, uint32_t max_width, uint32_t max_height)
{
if(ihdr->width > spng_u32max || !ihdr->width) return SPNG_EWIDTH;
Expand Down Expand Up @@ -3324,6 +3323,8 @@ int spng_decode_scanline(spng_ctx *ctx, void *out, size_t len)

if(fmt == SPNG_FMT_RGBA16) pixel_size = 8;
else if(fmt == SPNG_FMT_RGB8) pixel_size = 3;
else if(fmt == SPNG_FMT_GA8) pixel_size = 2;
else if(fmt == SPNG_FMT_G8) pixel_size = 1;

if(len < sub[pass].out_width) return SPNG_EBUFSIZ;

Expand All @@ -3346,12 +3347,6 @@ int spng_decode_scanline(spng_ctx *ctx, void *out, size_t len)
break;
}

if(f.unpack)
{
unpack_scanline(out, scanline, width, ihdr->bit_depth, fmt);
break;
}

if(ihdr->color_type == SPNG_COLOR_TYPE_TRUECOLOR)
{
if(ihdr->bit_depth == 16)
Expand Down Expand Up @@ -3519,6 +3514,30 @@ int spng_decode_scanline(spng_ctx *ctx, void *out, size_t len)
memcpy(pixel + 4, &b_16, 2);
memcpy(pixel + 6, &a_16, 2);
}
else if(fmt & (SPNG_FMT_G8 | SPNG_FMT_GA8))
{
if(ihdr->bit_depth == 16)
{
gray_8 = gray_16 >> 8;
a_8 = a_16 >> 8;
}

pixel[0] = gray_8;

if(fmt == SPNG_FMT_GA8) pixel[1] = a_8;
}
else if(fmt == SPNG_FMT_GA16)
{
if(ihdr->bit_depth != 16)
{
gray_16 = gray_8;
a_16 = a_8;
}

memcpy(pixel, &gray_16, 2);
memcpy(pixel + 2, &a_16, 2);
}

}/* for(k=0; k < width; k++) */

if(f.apply_trns) trns_row(out, scanline, trns_px, ctx->bytes_per_pixel, &ctx->ihdr, width, fmt);
Expand Down Expand Up @@ -3709,7 +3728,7 @@ int spng_decode_image(spng_ctx *ctx, void *out, size_t len, int fmt, int flags)
if(f.indexed) f.do_scaling = 0;

unsigned depth_target = 8; /* FMT_RGBA8, G8 */
if(fmt == SPNG_FMT_RGBA16) depth_target = 16;
if(fmt & (SPNG_FMT_RGBA16 | SPNG_FMT_GA16)) depth_target = 16;

if(flags & SPNG_DECODE_TRNS && ctx->stored.trns) f.apply_trns = 1;
else flags &= ~SPNG_DECODE_TRNS;
Expand Down Expand Up @@ -3742,24 +3761,22 @@ int spng_decode_image(spng_ctx *ctx, void *out, size_t len, int fmt, int flags)
f.apply_gamma = 0; /* for now */
f.apply_trns = 0;
}
else if(fmt == SPNG_FMT_G8 && ihdr->color_type == SPNG_COLOR_TYPE_GRAYSCALE && ihdr->bit_depth <= 8)
else if(fmt == SPNG_FMT_G8)
{
if(ihdr->bit_depth == depth_target) f.same_layout = 1;
else if(ihdr->bit_depth < 8) f.unpack = 1;
if(ihdr->color_type == SPNG_COLOR_TYPE_GRAYSCALE &&
ihdr->bit_depth == depth_target) f.same_layout = 1;

f.apply_trns = 0;
}
else if(fmt == SPNG_FMT_GA8 && ihdr->color_type == SPNG_COLOR_TYPE_GRAYSCALE && ihdr->bit_depth <= 8)
else if(fmt == SPNG_FMT_GA8)
{
if(ihdr->color_type == SPNG_COLOR_TYPE_GRAYSCALE_ALPHA &&
ihdr->bit_depth == depth_target) f.same_layout = 1;
else if(ihdr->bit_depth <= 8) f.unpack = 1;
}
else if(fmt == SPNG_FMT_GA16 && ihdr->color_type == SPNG_COLOR_TYPE_GRAYSCALE && ihdr->bit_depth == 16)
else if(fmt == SPNG_FMT_GA16)
{
if(ihdr->color_type == SPNG_COLOR_TYPE_GRAYSCALE_ALPHA &&
ihdr->bit_depth == depth_target) f.same_layout = 1;
else if(ihdr->bit_depth == 16) f.unpack = 1;
}

/*if(f.same_layout && !flags && !f.interlaced) f.zerocopy = 1;*/
Expand All @@ -3773,7 +3790,7 @@ int spng_decode_image(spng_ctx *ctx, void *out, size_t len, int fmt, int flags)

unsigned lut_entries;

if(fmt & (SPNG_FMT_RGBA8 | SPNG_FMT_RGB8))
if(fmt & (SPNG_FMT_RGBA8 | SPNG_FMT_RGB8 | SPNG_FMT_GA8 | SPNG_FMT_G8))
{
lut_entries = 256;
max = 255.0f;
Expand Down Expand Up @@ -3846,7 +3863,7 @@ int spng_decode_image(spng_ctx *ctx, void *out, size_t len, int fmt, int flags)
}
}

if(ihdr->bit_depth == 16 && fmt & (SPNG_FMT_RGBA8 | SPNG_FMT_RGB8))
if(ihdr->bit_depth == 16 && fmt & (SPNG_FMT_RGBA8 | SPNG_FMT_RGB8 | SPNG_FMT_GA8 | SPNG_FMT_G8))
{/* samples are scaled down by 8 bits in the decode loop */
sb->red_bits -= 8;
sb->green_bits -= 8;
Expand Down