image: add more varied downsample, pgm reader
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75d69bf9df
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208
image.cpp
208
image.cpp
@ -19,13 +19,109 @@
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#include "image.hpp"
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#include "debug.hpp"
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#include "except.hpp"
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#include "io.hpp"
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#include <fstream>
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//-----------------------------------------------------------------------------
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struct box {
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static constexpr float support = 0.5f;
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static constexpr float weight [[gnu::pure]] (float x)
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{
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return (x >= -0.5f && x <= 0.5f) ? 1.f : 0.f;
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}
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};
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//-----------------------------------------------------------------------------
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// XXX: Known to cause hard black ringing
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template <size_t S>
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struct lanczos {
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static constexpr float support = float {S};
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static float weight [[gnu::pure]] (float x)
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{
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if (x < 0.f)
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x = -x;
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if (x <= S)
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return sincn (x) * sincn (x / S);
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return 0.f;
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}
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};
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template struct lanczos< 3>;
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template struct lanczos< 4>;
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template struct lanczos< 6>;
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template struct lanczos<12>;
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//-----------------------------------------------------------------------------
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struct bspline {
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static constexpr float support = 2.f;
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static float weight [[gnu::pure]] (float x)
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{
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if (x < 0.f)
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x = -x;
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if (x < 1.f)
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return .5f * x * x * x - x * x + (2.f / 3.f);
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if (x < 2.f) {
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x = 2.f - x;
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return (1.f / 6.f) * x * x * x;
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}
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return 0.f;
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}
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};
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//-----------------------------------------------------------------------------
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// XXX: Known to cause hard black ringing
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struct mitchell {
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static constexpr float support = 2.f;
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static float weight [[gnu::pure]] (float x)
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{
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return eval (x, 1.f / 3.f, 1.f / 3.f);
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}
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private:
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static float eval (float x, float B, float C)
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{
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if (x < 0.f)
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x = -x;
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if (x < 1.f) {
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x = ( 12.f - 9.f * B - 6.f * C) * x * x * x
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+ (-18.f + 12.f * B + 6.f * C) * x * x
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+ 6.f - 2.f * B;
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return x / 6.f;
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}
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if (x < 2.f) {
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x = ( -1.f * B - 6.f * C) * x * x * x
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+ ( 6.f * B + 30.f * C) * x * x
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+ (-12.f * B - 48.f * C) * x
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+ 8.f * B + 24.f * C;
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return x / 6.f;
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}
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return 0.f;
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}
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};
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//-----------------------------------------------------------------------------
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template <typename T>
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util::image::buffer<T>::buffer (size_t _w, size_t _h, size_t _s):
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@ -110,38 +206,101 @@ util::image::buffer<T>::clone (void) const
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//-----------------------------------------------------------------------------
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// HACK: This code hasn't really been tested with multiple filters (it is
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// known to produce dark ringing artefacts with sinc) or robustly with
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// fractional factors. But... it works more or less.
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template <typename T>
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util::image::buffer<T>
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util::image::buffer<T>::downsample (unsigned factor)
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util::image::buffer<T>::downsample (float factor) const
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{
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CHECK_GE (factor, 1);
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if (factor == 1)
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return clone<T> ();
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CHECK_GE (factor, 0);
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size_t w_ = w / factor;
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size_t h_ = h / factor;
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size_t s_ = w_;
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using filter = bspline;
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CHECK_NEQ (w_, 0);
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CHECK_NEQ (h_, 0);
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const buffer &src = *this;
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buffer dst (static_cast<size_t> (w / factor),
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static_cast<size_t> (h / factor));
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buffer out { w_, h_, s_, std::make_unique<T[]> (w_ * h_) };
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const float scale = float (dst.w) / src.w;
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const float half_width = filter::support / scale;
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const int half_pixels = int (std::ceil (half_width));
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// Do a really shitty nearest neighbour average in src-space.
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for (size_t y = 0; y < out.h; ++y)
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for (size_t x = 0; x < out.w; ++x) {
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size_t src00 = (y + 0) * s * factor + (x * factor) + 0;
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size_t src01 = (y + 0) * s * factor + (x * factor) + 1;
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size_t src10 = (y + 1) * s * factor + (x * factor) + 0;
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size_t src11 = (y + 1) * s * factor + (x * factor) + 1;
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// Calculate the weighted sum of the src pixels for each dst pixel
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for (size_t d_y = 0; d_y < dst.h; ++d_y)
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for (size_t d_x = 0; d_x < dst.w; ++d_x) {
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// Initialise value and weight sums
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float v = 0.f;
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float m = 0.f;
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out.data[x + y * out.s] = (data[src00] + data[src01] + data[src10] + data[src11]) / 4;
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// Find the centre of the src pixel
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float o_y = (d_y + 0.5f) / scale;
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float o_x = (d_x + 0.5f) / scale;
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// Do a full summation across the window. This isn't using
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// seperable filtering because:
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// a) we need high precision with fractional factors
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// b) it's much easier to implement as is
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//
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// TODO: seperable filters
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for (int s_y = -half_pixels; s_y <= half_pixels; ++s_y)
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for (int s_x = -half_pixels; s_x <= half_pixels; ++s_x) {
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float m_x = filter::weight (s_x * scale);
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float m_y = filter::weight (s_y * scale);
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float m_ = m_x * m_y;
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// Simple clamp to border for edges
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int x = int (limit (o_x + s_x - 0.5f, 0, src.w));
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int y = int (limit (o_y + s_y - 0.5f, 0, src.h));
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// Collection the contribution
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v += m_ * src.data[y * src.s + x];
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m += m_;
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}
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CHECK_NEZ (m);
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dst.data[d_y * dst.s + d_x] = uint8_t (v / m);
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}
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return dst;
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}
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//-----------------------------------------------------------------------------
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// HACK: This does not support the full header structure with any robustness.
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// In particular it will abort when it sees a comment. If you want better
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// support use waif, or port its implementation.
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util::image::buffer<uint8_t>
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util::pgm::read (const boost::filesystem::path &path)
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{
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util::mapped_file raw (path);
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std::ifstream cooked (path.c_str (), std::ios::binary);
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char magic[2];
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size_t width, height, scale;
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char space;
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cooked >> magic[0] >> magic[1] >> width >> height >> scale >> space;
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if (magic[0] != 'P' && magic[1] != '5')
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throw std::runtime_error ("invalid header magic");
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if (width == 0 || height == 0 || scale == 0)
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throw std::runtime_error ("zero width, height, or scale");
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size_t expected = width * height;
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size_t remain = raw.size () - cooked.tellg ();
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if (expected != remain)
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throw std::runtime_error ("expected data size mismatch");
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util::image::buffer<uint8_t> out (width, height);
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CHECK_EQ (out.w, out.s);
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std::copy (raw.begin () + cooked.tellg () - 1, raw.end (), out.data.get ());
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return out;
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}
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//-----------------------------------------------------------------------------
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static void
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write_netpbm (const uint8_t *restrict pixels,
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@ -174,6 +333,15 @@ write_netpbm (const uint8_t *restrict pixels,
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}
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//-----------------------------------------------------------------------------
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void
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util::pgm::write (const util::image::buffer<uint8_t> &src,
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const boost::filesystem::path &path)
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{
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write (src.data.get (), src.w, src.h, src.s, path);
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}
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//-----------------------------------------------------------------------------
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void
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util::pgm::write (const uint8_t *restrict pixels,
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@ -45,7 +45,7 @@ namespace util {
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template <typename U>
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buffer<U> clone (void) const;
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buffer<T> downsample (unsigned factor);
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buffer<T> downsample (float factor) const;
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size_t w;
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size_t h;
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@ -57,6 +57,11 @@ namespace util {
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struct pgm {
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static image::buffer<uint8_t> read (const boost::filesystem::path&);
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static void write (const image::buffer<uint8_t> &src,
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const boost::filesystem::path &);
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static void write (const uint8_t *restrict pixels,
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size_t width,
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size_t height,
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