66 lines
2.0 KiB
C++
66 lines
2.0 KiB
C++
// Copyright 2023 The MediaPipe Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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#include "Halide.h"
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namespace {
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class RgbGray : public Halide::Generator<RgbGray> {
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public:
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Var x{"x"}, y{"y"}, c{"c"};
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Input<Buffer<uint8_t, 3>> src_rgb{"rgb"};
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Output<Buffer<uint8_t, 2>> convert{"convert"};
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void generate();
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void schedule();
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};
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// Integer math versions of the full-range JFIF RGB-Y coefficients.
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// Y = 0.2990*R + 0.5870*G + 0.1140*B
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// See https://www.w3.org/Graphics/JPEG/jfif3.pdf. These coefficients are
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// similar to, but not identical, to those used in Android.
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Halide::Expr rgby(Halide::Expr r, Halide::Expr g, Halide::Expr b) {
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r = Halide::cast<int32_t>(r);
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g = Halide::cast<int32_t>(g);
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b = Halide::cast<int32_t>(b);
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return (19595 * r + 38470 * g + 7474 * b + 32768) >> 16;
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}
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void RgbGray::generate() {
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Halide::Func gray("gray");
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gray(x, y) = rgby(src_rgb(x, y, 0), src_rgb(x, y, 1), src_rgb(x, y, 2));
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convert(x, y) = Halide::saturating_cast<uint8_t>(gray(x, y));
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}
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void RgbGray::schedule() {
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// RGB images starts at index zero in every dimension.
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src_rgb.dim(0).set_min(0);
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src_rgb.dim(1).set_min(0);
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src_rgb.dim(2).set_min(0);
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// Require that the input buffer be interleaved and tightly-packed;
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// with no gaps between pixels.
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src_rgb.dim(0).set_stride(src_rgb.dim(2).extent());
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src_rgb.dim(2).set_stride(1);
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// Grayscale images starts at index zero in every dimension.
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convert.dim(0).set_min(0);
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convert.dim(1).set_min(0);
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}
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} // namespace
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HALIDE_REGISTER_GENERATOR(RgbGray, rgb_gray_generator)
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