image: add more varied downsample, pgm reader

This commit is contained in:
Danny Robson 2015-02-05 20:34:38 +11:00
parent 75d69bf9df
commit 1290cde443
2 changed files with 194 additions and 21 deletions

208
image.cpp
View File

@ -19,13 +19,109 @@
#include "image.hpp"
#include "debug.hpp"
#include "except.hpp"
#include "io.hpp"
#include <fstream>
//-----------------------------------------------------------------------------
struct box {
static constexpr float support = 0.5f;
static constexpr float weight [[gnu::pure]] (float x)
{
return (x >= -0.5f && x <= 0.5f) ? 1.f : 0.f;
}
};
//-----------------------------------------------------------------------------
// XXX: Known to cause hard black ringing
template <size_t S>
struct lanczos {
static constexpr float support = float {S};
static float weight [[gnu::pure]] (float x)
{
if (x < 0.f)
x = -x;
if (x <= S)
return sincn (x) * sincn (x / S);
return 0.f;
}
};
template struct lanczos< 3>;
template struct lanczos< 4>;
template struct lanczos< 6>;
template struct lanczos<12>;
//-----------------------------------------------------------------------------
struct bspline {
static constexpr float support = 2.f;
static float weight [[gnu::pure]] (float x)
{
if (x < 0.f)
x = -x;
if (x < 1.f)
return .5f * x * x * x - x * x + (2.f / 3.f);
if (x < 2.f) {
x = 2.f - x;
return (1.f / 6.f) * x * x * x;
}
return 0.f;
}
};
//-----------------------------------------------------------------------------
// XXX: Known to cause hard black ringing
struct mitchell {
static constexpr float support = 2.f;
static float weight [[gnu::pure]] (float x)
{
return eval (x, 1.f / 3.f, 1.f / 3.f);
}
private:
static float eval (float x, float B, float C)
{
if (x < 0.f)
x = -x;
if (x < 1.f) {
x = ( 12.f - 9.f * B - 6.f * C) * x * x * x
+ (-18.f + 12.f * B + 6.f * C) * x * x
+ 6.f - 2.f * B;
return x / 6.f;
}
if (x < 2.f) {
x = ( -1.f * B - 6.f * C) * x * x * x
+ ( 6.f * B + 30.f * C) * x * x
+ (-12.f * B - 48.f * C) * x
+ 8.f * B + 24.f * C;
return x / 6.f;
}
return 0.f;
}
};
//-----------------------------------------------------------------------------
template <typename T>
util::image::buffer<T>::buffer (size_t _w, size_t _h, size_t _s):
@ -110,38 +206,101 @@ util::image::buffer<T>::clone (void) const
//-----------------------------------------------------------------------------
// HACK: This code hasn't really been tested with multiple filters (it is
// known to produce dark ringing artefacts with sinc) or robustly with
// fractional factors. But... it works more or less.
template <typename T>
util::image::buffer<T>
util::image::buffer<T>::downsample (unsigned factor)
util::image::buffer<T>::downsample (float factor) const
{
CHECK_GE (factor, 1);
if (factor == 1)
return clone<T> ();
CHECK_GE (factor, 0);
size_t w_ = w / factor;
size_t h_ = h / factor;
size_t s_ = w_;
using filter = bspline;
CHECK_NEQ (w_, 0);
CHECK_NEQ (h_, 0);
const buffer &src = *this;
buffer dst (static_cast<size_t> (w / factor),
static_cast<size_t> (h / factor));
buffer out { w_, h_, s_, std::make_unique<T[]> (w_ * h_) };
const float scale = float (dst.w) / src.w;
const float half_width = filter::support / scale;
const int half_pixels = int (std::ceil (half_width));
// Do a really shitty nearest neighbour average in src-space.
for (size_t y = 0; y < out.h; ++y)
for (size_t x = 0; x < out.w; ++x) {
size_t src00 = (y + 0) * s * factor + (x * factor) + 0;
size_t src01 = (y + 0) * s * factor + (x * factor) + 1;
size_t src10 = (y + 1) * s * factor + (x * factor) + 0;
size_t src11 = (y + 1) * s * factor + (x * factor) + 1;
// Calculate the weighted sum of the src pixels for each dst pixel
for (size_t d_y = 0; d_y < dst.h; ++d_y)
for (size_t d_x = 0; d_x < dst.w; ++d_x) {
// Initialise value and weight sums
float v = 0.f;
float m = 0.f;
out.data[x + y * out.s] = (data[src00] + data[src01] + data[src10] + data[src11]) / 4;
// Find the centre of the src pixel
float o_y = (d_y + 0.5f) / scale;
float o_x = (d_x + 0.5f) / scale;
// Do a full summation across the window. This isn't using
// seperable filtering because:
// a) we need high precision with fractional factors
// b) it's much easier to implement as is
//
// TODO: seperable filters
for (int s_y = -half_pixels; s_y <= half_pixels; ++s_y)
for (int s_x = -half_pixels; s_x <= half_pixels; ++s_x) {
float m_x = filter::weight (s_x * scale);
float m_y = filter::weight (s_y * scale);
float m_ = m_x * m_y;
// Simple clamp to border for edges
int x = int (limit (o_x + s_x - 0.5f, 0, src.w));
int y = int (limit (o_y + s_y - 0.5f, 0, src.h));
// Collection the contribution
v += m_ * src.data[y * src.s + x];
m += m_;
}
CHECK_NEZ (m);
dst.data[d_y * dst.s + d_x] = uint8_t (v / m);
}
return dst;
}
//-----------------------------------------------------------------------------
// HACK: This does not support the full header structure with any robustness.
// In particular it will abort when it sees a comment. If you want better
// support use waif, or port its implementation.
util::image::buffer<uint8_t>
util::pgm::read (const boost::filesystem::path &path)
{
util::mapped_file raw (path);
std::ifstream cooked (path.c_str (), std::ios::binary);
char magic[2];
size_t width, height, scale;
char space;
cooked >> magic[0] >> magic[1] >> width >> height >> scale >> space;
if (magic[0] != 'P' && magic[1] != '5')
throw std::runtime_error ("invalid header magic");
if (width == 0 || height == 0 || scale == 0)
throw std::runtime_error ("zero width, height, or scale");
size_t expected = width * height;
size_t remain = raw.size () - cooked.tellg ();
if (expected != remain)
throw std::runtime_error ("expected data size mismatch");
util::image::buffer<uint8_t> out (width, height);
CHECK_EQ (out.w, out.s);
std::copy (raw.begin () + cooked.tellg () - 1, raw.end (), out.data.get ());
return out;
}
//-----------------------------------------------------------------------------
static void
write_netpbm (const uint8_t *restrict pixels,
@ -174,6 +333,15 @@ write_netpbm (const uint8_t *restrict pixels,
}
//-----------------------------------------------------------------------------
void
util::pgm::write (const util::image::buffer<uint8_t> &src,
const boost::filesystem::path &path)
{
write (src.data.get (), src.w, src.h, src.s, path);
}
//-----------------------------------------------------------------------------
void
util::pgm::write (const uint8_t *restrict pixels,

View File

@ -45,7 +45,7 @@ namespace util {
template <typename U>
buffer<U> clone (void) const;
buffer<T> downsample (unsigned factor);
buffer<T> downsample (float factor) const;
size_t w;
size_t h;
@ -57,6 +57,11 @@ namespace util {
struct pgm {
static image::buffer<uint8_t> read (const boost::filesystem::path&);
static void write (const image::buffer<uint8_t> &src,
const boost::filesystem::path &);
static void write (const uint8_t *restrict pixels,
size_t width,
size_t height,