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initial defiltering implementation (potentially broken)

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Luna 2025-07-11 07:54:52 +02:00
parent 7c09fa42a7
commit 5b4d489b79
1 changed files with 152 additions and 2 deletions
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154
lily_png.cpp
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@ -22,6 +22,57 @@ static metadata parse_metadata(buffer &data)
return m;
}
static size_t get_pixel_bit_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)
{
ret = meta.bit_depth;
}
else
throw std::runtime_error("Invalid bit depht");
break;
case 2:
if (meta.bit_depth == 8 || meta.bit_depth == 16)
{
ret = meta.bit_depth * 3;
}
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)
{
ret = meta.bit_depth;
}
else
throw std::runtime_error("Invalid bit depht");
break;
case 4:
if (meta.bit_depth == 8 || meta.bit_depth == 16)
{
ret = meta.bit_depth * 2;
}
else
throw std::runtime_error("Invalid bit depht");
break;
case 6:
if (meta.bit_depth == 8 || meta.bit_depth == 16)
{
ret = meta.bit_depth * 4;
}
else
throw std::runtime_error("Invalid bit depht");
break;
default:
throw std::runtime_error("Invalid color type");
}
return ret;
}
static size_t get_uncompressed_size(const metadata meta)
{
size_t ret = 0;
@ -79,7 +130,7 @@ static size_t get_uncompressed_size(const metadata meta)
return ret;
}
void read_png(const std::string &file_path, buffer_unsigned &data)
static void read_raw_data(const std::string &file_path, buffer_unsigned &data, metadata &meta)
{
unsigned char magic[9] = {137, 80, 78, 71, 13, 10, 26, 10};
file_reader reader(file_path);
@ -91,7 +142,6 @@ void read_png(const std::string &file_path, buffer_unsigned &data)
return ;
}
buffer_unsigned raw_dat{};
metadata meta{};
while (true)
{
std::tuple<unsigned int, buffer> chunk_header;
@ -142,3 +192,103 @@ void read_png(const std::string &file_path, buffer_unsigned &data)
throw std::runtime_error("Uncompress fail");
}
}
template <typename T>
T paeth_predict(T a, T b, T c)
{
T pred = a+b-c;
T pred1 = abs(pred - a);
T pred2 = abs(pred - b);
T pred3 = abs(pred - c);
if (pred1 <= pred2 && pred1 <= pred3)
return a;
if (pred2 <= pred3)
return b;
return c;
}
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);
unsigned long scanlines = 0;
dest.allocate(get_uncompressed_size(meta));
while (scanlines < meta.height)
{
unsigned char filter = 0;
for (int i = 0; i < (pixel_size/8) * meta.width + 1; i++)
{
if (i == 0)
{
filter = data.data[index + i];
continue;
}
long index_before = 0;
long index_before2 = 0;
long index_before3 = 0;
switch (filter)
{
case 0:
dest.data[index_dest] = data.data[index + i];
break;
case 1:
if (pixel_size < 8)
index_before = index + i - 1;
else
index_before = index + i - pixel_size/8;
if (index_before <= 0)
break;
dest.data[index_dest] = data.data[index + i] + dest.data[index_before];
break;
case 2:
index_before = (index + i) - (meta.width * (pixel_size/8));
if (index_before <= 0)
break;
dest.data[index_dest] = data.data[index + i] + dest.data[index_before];
break;
case 3:
if (pixel_size < 8)
index_before = index + i - 1;
else
index_before = index + i - pixel_size/8;
if (index_before <= 0)
break;
index_before2 = (index + i) - (meta.width * (pixel_size/8));
dest.data[index_dest] = data.data[index + i] + floor((dest.data[index_before] + dest.data[index_before2])/2);
break;
case 4:
if (pixel_size < 8)
index_before = index + i - 1;
else
index_before = index + i - pixel_size/8;
if (index_before <= 0)
break;
index_before2 = (index + i) - (meta.width * (pixel_size/8));
index_before3 = 0;
if (pixel_size < 8)
index_before3 = index_before2 + i - 1;
else
index_before3 = index_before2 + i - pixel_size/8;
if (index_before3 <= 0)
break;
dest.data[index_dest] = data.data[index + i] + paeth_predict(dest.data[index_before], dest.data[index_before2], dest.data[index_before3]);
break;
default:
std::println("Non standard filter");
break;
}
index_dest++;
}
index += (pixel_size/8) * meta.width + 1;
scanlines++;
}
}
void read_png(const std::string &file_path, buffer_unsigned &data)
{
buffer_unsigned tmp_data{};
metadata meta{0};
read_raw_data(file_path, tmp_data, meta);
filter(tmp_data, data, meta);
}