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image: add support for image/jpeg and image/png (#303)
* Copy from go1.17 image package * Remove unnecessary files * Reduce memory usage * Add examples/ili9341/slideshow * image: add ./image/README.md * image: change convert2bin to . /cmd * Makefile: add ./cmd to NOTEST
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// Copyright 2009 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package jpeg
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// This is a Go translation of idct.c from
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//
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// http://standards.iso.org/ittf/PubliclyAvailableStandards/ISO_IEC_13818-4_2004_Conformance_Testing/Video/verifier/mpeg2decode_960109.tar.gz
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//
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// which carries the following notice:
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/* Copyright (C) 1996, MPEG Software Simulation Group. All Rights Reserved. */
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/*
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* Disclaimer of Warranty
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*
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* These software programs are available to the user without any license fee or
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* royalty on an "as is" basis. The MPEG Software Simulation Group disclaims
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* any and all warranties, whether express, implied, or statuary, including any
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* implied warranties or merchantability or of fitness for a particular
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* purpose. In no event shall the copyright-holder be liable for any
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* incidental, punitive, or consequential damages of any kind whatsoever
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* arising from the use of these programs.
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*
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* This disclaimer of warranty extends to the user of these programs and user's
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* customers, employees, agents, transferees, successors, and assigns.
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*
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* The MPEG Software Simulation Group does not represent or warrant that the
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* programs furnished hereunder are free of infringement of any third-party
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* patents.
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*
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* Commercial implementations of MPEG-1 and MPEG-2 video, including shareware,
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* are subject to royalty fees to patent holders. Many of these patents are
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* general enough such that they are unavoidable regardless of implementation
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* design.
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*
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*/
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const blockSize = 64 // A DCT block is 8x8.
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type block [blockSize]int32
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const (
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w1 = 2841 // 2048*sqrt(2)*cos(1*pi/16)
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w2 = 2676 // 2048*sqrt(2)*cos(2*pi/16)
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w3 = 2408 // 2048*sqrt(2)*cos(3*pi/16)
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w5 = 1609 // 2048*sqrt(2)*cos(5*pi/16)
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w6 = 1108 // 2048*sqrt(2)*cos(6*pi/16)
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w7 = 565 // 2048*sqrt(2)*cos(7*pi/16)
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w1pw7 = w1 + w7
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w1mw7 = w1 - w7
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w2pw6 = w2 + w6
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w2mw6 = w2 - w6
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w3pw5 = w3 + w5
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w3mw5 = w3 - w5
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r2 = 181 // 256/sqrt(2)
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)
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// idct performs a 2-D Inverse Discrete Cosine Transformation.
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//
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// The input coefficients should already have been multiplied by the
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// appropriate quantization table. We use fixed-point computation, with the
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// number of bits for the fractional component varying over the intermediate
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// stages.
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//
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// For more on the actual algorithm, see Z. Wang, "Fast algorithms for the
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// discrete W transform and for the discrete Fourier transform", IEEE Trans. on
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// ASSP, Vol. ASSP- 32, pp. 803-816, Aug. 1984.
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func idct(src *block) {
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// Horizontal 1-D IDCT.
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for y := 0; y < 8; y++ {
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y8 := y * 8
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s := src[y8 : y8+8 : y8+8] // Small cap improves performance, see https://golang.org/issue/27857
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// If all the AC components are zero, then the IDCT is trivial.
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if s[1] == 0 && s[2] == 0 && s[3] == 0 &&
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s[4] == 0 && s[5] == 0 && s[6] == 0 && s[7] == 0 {
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dc := s[0] << 3
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s[0] = dc
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s[1] = dc
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s[2] = dc
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s[3] = dc
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s[4] = dc
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s[5] = dc
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s[6] = dc
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s[7] = dc
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continue
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}
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// Prescale.
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x0 := (s[0] << 11) + 128
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x1 := s[4] << 11
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x2 := s[6]
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x3 := s[2]
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x4 := s[1]
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x5 := s[7]
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x6 := s[5]
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x7 := s[3]
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// Stage 1.
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x8 := w7 * (x4 + x5)
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x4 = x8 + w1mw7*x4
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x5 = x8 - w1pw7*x5
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x8 = w3 * (x6 + x7)
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x6 = x8 - w3mw5*x6
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x7 = x8 - w3pw5*x7
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// Stage 2.
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x8 = x0 + x1
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x0 -= x1
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x1 = w6 * (x3 + x2)
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x2 = x1 - w2pw6*x2
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x3 = x1 + w2mw6*x3
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x1 = x4 + x6
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x4 -= x6
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x6 = x5 + x7
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x5 -= x7
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// Stage 3.
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x7 = x8 + x3
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x8 -= x3
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x3 = x0 + x2
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x0 -= x2
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x2 = (r2*(x4+x5) + 128) >> 8
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x4 = (r2*(x4-x5) + 128) >> 8
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// Stage 4.
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s[0] = (x7 + x1) >> 8
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s[1] = (x3 + x2) >> 8
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s[2] = (x0 + x4) >> 8
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s[3] = (x8 + x6) >> 8
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s[4] = (x8 - x6) >> 8
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s[5] = (x0 - x4) >> 8
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s[6] = (x3 - x2) >> 8
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s[7] = (x7 - x1) >> 8
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}
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// Vertical 1-D IDCT.
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for x := 0; x < 8; x++ {
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// Similar to the horizontal 1-D IDCT case, if all the AC components are zero, then the IDCT is trivial.
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// However, after performing the horizontal 1-D IDCT, there are typically non-zero AC components, so
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// we do not bother to check for the all-zero case.
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s := src[x : x+57 : x+57] // Small cap improves performance, see https://golang.org/issue/27857
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// Prescale.
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y0 := (s[8*0] << 8) + 8192
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y1 := s[8*4] << 8
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y2 := s[8*6]
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y3 := s[8*2]
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y4 := s[8*1]
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y5 := s[8*7]
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y6 := s[8*5]
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y7 := s[8*3]
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// Stage 1.
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y8 := w7*(y4+y5) + 4
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y4 = (y8 + w1mw7*y4) >> 3
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y5 = (y8 - w1pw7*y5) >> 3
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y8 = w3*(y6+y7) + 4
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y6 = (y8 - w3mw5*y6) >> 3
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y7 = (y8 - w3pw5*y7) >> 3
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// Stage 2.
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y8 = y0 + y1
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y0 -= y1
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y1 = w6*(y3+y2) + 4
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y2 = (y1 - w2pw6*y2) >> 3
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y3 = (y1 + w2mw6*y3) >> 3
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y1 = y4 + y6
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y4 -= y6
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y6 = y5 + y7
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y5 -= y7
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// Stage 3.
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y7 = y8 + y3
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y8 -= y3
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y3 = y0 + y2
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y0 -= y2
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y2 = (r2*(y4+y5) + 128) >> 8
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y4 = (r2*(y4-y5) + 128) >> 8
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// Stage 4.
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s[8*0] = (y7 + y1) >> 14
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s[8*1] = (y3 + y2) >> 14
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s[8*2] = (y0 + y4) >> 14
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s[8*3] = (y8 + y6) >> 14
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s[8*4] = (y8 - y6) >> 14
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s[8*5] = (y0 - y4) >> 14
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s[8*6] = (y3 - y2) >> 14
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s[8*7] = (y7 - y1) >> 14
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}
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}
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