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Now defiltering works properly, it was caused to bad bit size calculation of pixel boundaries

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Luna 2025-07-13 18:39:22 +02:00
parent b8cb54b034
commit 0320618494
1 changed files with 25 additions and 80 deletions
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105
lily_png.cpp
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@ -76,57 +76,8 @@ static size_t get_pixel_bit_size(const metadata &meta)
static size_t get_uncompressed_size(const metadata meta)
{
size_t ret = 0;
switch (meta.color_type)
{
case 0:
if (meta.bit_depth == 1 || meta.bit_depth == 2 || meta.bit_depth == 4 || meta.bit_depth == 8 || meta.bit_depth == 16)
{
size_t size_per_row = ceil((meta.width * (meta.bit_depth))/8) + 1;
ret = size_per_row * meta.height;
}
else
throw std::runtime_error("Invalid bit depht");
break;
case 2:
if (meta.bit_depth == 8 || meta.bit_depth == 16)
{
size_t size_per_row = ceil((meta.width * (meta.bit_depth * 3))/8) + 1;
ret = size_per_row * meta.height;
}
else
throw std::runtime_error("Invalid bit depht");
break;
case 3:
if (meta.bit_depth == 1 || meta.bit_depth == 2 || meta.bit_depth == 4 || meta.bit_depth == 8)
{
size_t size_per_row = ceil((meta.width * (meta.bit_depth))/8) + 1;
ret = size_per_row * meta.height;
}
else
throw std::runtime_error("Invalid bit depht");
break;
case 4:
if (meta.bit_depth == 8 || meta.bit_depth == 16)
{
size_t size_per_row = ceil((meta.width * (meta.bit_depth * 2))/8) + 1;
ret = size_per_row * meta.height;
}
else
throw std::runtime_error("Invalid bit depht");
break;
case 6:
if (meta.bit_depth == 8 || meta.bit_depth == 16)
{
size_t size_per_row = ceil((meta.width * (meta.bit_depth * 4))/8) + 1;
ret = size_per_row * meta.height;
}
else
throw std::runtime_error("Invalid bit depht");
break;
default:
throw std::runtime_error("Invalid color type");
}
size_t ret = (meta.width * get_pixel_bit_size(meta) + 7)/8; //ceil() but for bytes
ret = (ret + 1) * meta.height;
std::println("Uncompressed size {}", ret);
return ret;
}
@ -210,46 +161,38 @@ int paeth_predict(int a, int b, int c)
static void filter_scanline(unsigned char *scanline, unsigned char *previous_scanline, unsigned char *dest, metadata &meta, unsigned char filter_type)
{
size_t pixel_size = get_pixel_bit_size(meta);
for (int i = 0; i < ceil(pixel_size/8.0f) * meta.width; i++)
size_t pixel_size_bytes = (pixel_size + 7)/8;
size_t scanline_size = (meta.width * pixel_size + 7)/8;
for (int i = 0; i < scanline_size; i++)
{
long index_before = 0;
unsigned char a = 0;
unsigned char b = 0;
unsigned char c = 0;
if (i >= pixel_size_bytes)
a = dest[i - pixel_size_bytes];
if (previous_scanline != nullptr)
b = previous_scanline[i];
if (previous_scanline != nullptr && i >= pixel_size_bytes)
c = previous_scanline[i - pixel_size_bytes];
switch (filter_type)
{
case 0:
dest[i] = scanline[i];
break;
case 1:
if (pixel_size < 8)
index_before = i - 1;
else
index_before = i - ceil(pixel_size/8.0f);
if (index_before <= 0)
dest[i] = scanline[i] + 0;
else
dest[i] = scanline[i] + dest[index_before];
dest[i] = scanline[i] + a;
break;
case 2:
dest[i] = scanline[i] + previous_scanline[i];
dest[i] = scanline[i] + b;
break;
case 3:
if (pixel_size < 8)
index_before = i - 1;
else
index_before = i - ceil(pixel_size/8.0f);
if (index_before <= 0)
dest[i] = scanline[i] + floor((0 + previous_scanline[i])/2);
else
dest[i] = scanline[i] + floor((dest[index_before] + previous_scanline[i])/2);
dest[i] = scanline[i] + floor((a + b)/2);
break;
case 4:
if (pixel_size < 8)
index_before = i - 1;
else
index_before = i - ceil(pixel_size/8.0f);
if (index_before <= 0)
dest[i] = scanline[i] + paeth_predict(0, previous_scanline[i], 0);
else
dest[i] = scanline[i] + paeth_predict(dest[index_before], previous_scanline[i], previous_scanline[index_before]);
dest[i] = scanline[i] + paeth_predict(a, b, c);
break;
default:
std::println("Non standard filter");
@ -263,6 +206,8 @@ static void filter(buffer_unsigned &data, buffer_unsigned &dest ,metadata &meta)
unsigned long index = 0;
unsigned long index_dest = 0;
size_t pixel_size = get_pixel_bit_size(meta);
size_t pixel_size_bytes = (pixel_size + 7)/8;
size_t scanline_size = (meta.width * pixel_size + 7)/8;
unsigned long scanlines = 0;
dest.allocate(get_uncompressed_size(meta));
unsigned char *previous_scanline = nullptr;
@ -270,10 +215,10 @@ static void filter(buffer_unsigned &data, buffer_unsigned &dest ,metadata &meta)
{
unsigned char filter = data.data[index];
std::println("Filter {}", filter);
filter_scanline(&data.data[index++], previous_scanline, &dest.data[index_dest], meta, filter);
filter_scanline(&data.data[index + 1], previous_scanline, &dest.data[index_dest], meta, filter);
previous_scanline = &dest.data[index_dest];
index += ceil(pixel_size/8.0f) * meta.width;
index_dest += ceil(pixel_size/8.0f) * meta.width;
index += scanline_size + 1;
index_dest += scanline_size;
scanlines++;
}
}