/* * Copyright (c) 2010 The WebM project authors. All Rights Reserved. * * Use of this source code is governed by a BSD-style license * that can be found in the LICENSE file in the root of the source * tree. An additional intellectual property rights grant can be found * in the file PATENTS. All contributing project authors may * be found in the AUTHORS file in the root of the source tree. * * Based on code from the OggTheora software codec source code, * Copyright (C) 2002-2010 The Xiph.Org Foundation and contributors. */ #include <assert.h> #include <errno.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include "vpx/vpx_integer.h" #include "y4minput.h" // Reads 'size' bytes from 'file' into 'buf' with some fault tolerance. // Returns true on success. static int file_read(void *buf, size_t size, FILE *file) { … } static int y4m_parse_tags(y4m_input *_y4m, char *_tags) { … } // Copy a single tag into the buffer, along with a null character. // Returns 0 if any file IO errors occur. static int copy_tag(char *buf, size_t buf_len, char *end_tag, FILE *file) { … } /* Returns 1 if tags were parsed successfully, 0 otherwise. */ static int parse_tags(y4m_input *y4m_ctx, FILE *file) { … } /*All anti-aliasing filters in the following conversion functions are based on one of two window functions: The 6-tap Lanczos window (for down-sampling and shifts): sinc(\pi*t)*sinc(\pi*t/3), |t|<3 (sinc(t)==sin(t)/t) 0, |t|>=3 The 4-tap Mitchell window (for up-sampling): 7|t|^3-12|t|^2+16/3, |t|<1 -(7/3)|x|^3+12|x|^2-20|x|+32/3, |t|<2 0, |t|>=2 The number of taps is intentionally kept small to reduce computational overhead and limit ringing. The taps from these filters are scaled so that their sum is 1, and the result is scaled by 128 and rounded to integers to create a filter whose intermediate values fit inside 16 bits. Coefficients are rounded in such a way as to ensure their sum is still 128, which is usually equivalent to normal rounding. Conversions which require both horizontal and vertical filtering could have these steps pipelined, for less memory consumption and better cache performance, but we do them separately for simplicity.*/ #define OC_MINI(_a, _b) … #define OC_MAXI(_a, _b) … #define OC_CLAMPI(_a, _b, _c) … /*420jpeg chroma samples are sited like: Y-------Y-------Y-------Y------- | | | | | BR | | BR | | | | | Y-------Y-------Y-------Y------- | | | | | | | | | | | | Y-------Y-------Y-------Y------- | | | | | BR | | BR | | | | | Y-------Y-------Y-------Y------- | | | | | | | | | | | | 420mpeg2 chroma samples are sited like: Y-------Y-------Y-------Y------- | | | | BR | BR | | | | | Y-------Y-------Y-------Y------- | | | | | | | | | | | | Y-------Y-------Y-------Y------- | | | | BR | BR | | | | | Y-------Y-------Y-------Y------- | | | | | | | | | | | | We use a resampling filter to shift the site locations one quarter pixel (at the chroma plane's resolution) to the right. The 4:2:2 modes look exactly the same, except there are twice as many chroma lines, and they are vertically co-sited with the luma samples in both the mpeg2 and jpeg cases (thus requiring no vertical resampling).*/ static void y4m_42xmpeg2_42xjpeg_helper(unsigned char *_dst, const unsigned char *_src, int _c_w, int _c_h) { … } /*This format is only used for interlaced content, but is included for completeness. 420jpeg chroma samples are sited like: Y-------Y-------Y-------Y------- | | | | | BR | | BR | | | | | Y-------Y-------Y-------Y------- | | | | | | | | | | | | Y-------Y-------Y-------Y------- | | | | | BR | | BR | | | | | Y-------Y-------Y-------Y------- | | | | | | | | | | | | 420paldv chroma samples are sited like: YR------Y-------YR------Y------- | | | | | | | | | | | | YB------Y-------YB------Y------- | | | | | | | | | | | | YR------Y-------YR------Y------- | | | | | | | | | | | | YB------Y-------YB------Y------- | | | | | | | | | | | | We use a resampling filter to shift the site locations one quarter pixel (at the chroma plane's resolution) to the right. Then we use another filter to move the C_r location down one quarter pixel, and the C_b location up one quarter pixel.*/ static void y4m_convert_42xpaldv_42xjpeg(y4m_input *_y4m, unsigned char *_dst, unsigned char *_aux) { … } /*Perform vertical filtering to reduce a single plane from 4:2:2 to 4:2:0. This is used as a helper by several converation routines.*/ static void y4m_422jpeg_420jpeg_helper(unsigned char *_dst, const unsigned char *_src, int _c_w, int _c_h) { … } /*420jpeg chroma samples are sited like: Y-------Y-------Y-------Y------- | | | | | BR | | BR | | | | | Y-------Y-------Y-------Y------- | | | | | | | | | | | | Y-------Y-------Y-------Y------- | | | | | BR | | BR | | | | | Y-------Y-------Y-------Y------- | | | | | | | | | | | | 422jpeg chroma samples are sited like: Y---BR--Y-------Y---BR--Y------- | | | | | | | | | | | | Y---BR--Y-------Y---BR--Y------- | | | | | | | | | | | | Y---BR--Y-------Y---BR--Y------- | | | | | | | | | | | | Y---BR--Y-------Y---BR--Y------- | | | | | | | | | | | | We use a resampling filter to decimate the chroma planes by two in the vertical direction.*/ static void y4m_convert_422jpeg_420jpeg(y4m_input *_y4m, unsigned char *_dst, unsigned char *_aux) { … } /*420jpeg chroma samples are sited like: Y-------Y-------Y-------Y------- | | | | | BR | | BR | | | | | Y-------Y-------Y-------Y------- | | | | | | | | | | | | Y-------Y-------Y-------Y------- | | | | | BR | | BR | | | | | Y-------Y-------Y-------Y------- | | | | | | | | | | | | 422 chroma samples are sited like: YBR-----Y-------YBR-----Y------- | | | | | | | | | | | | YBR-----Y-------YBR-----Y------- | | | | | | | | | | | | YBR-----Y-------YBR-----Y------- | | | | | | | | | | | | YBR-----Y-------YBR-----Y------- | | | | | | | | | | | | We use a resampling filter to shift the original site locations one quarter pixel (at the original chroma resolution) to the right. Then we use a second resampling filter to decimate the chroma planes by two in the vertical direction.*/ static void y4m_convert_422_420jpeg(y4m_input *_y4m, unsigned char *_dst, unsigned char *_aux) { … } /*420jpeg chroma samples are sited like: Y-------Y-------Y-------Y------- | | | | | BR | | BR | | | | | Y-------Y-------Y-------Y------- | | | | | | | | | | | | Y-------Y-------Y-------Y------- | | | | | BR | | BR | | | | | Y-------Y-------Y-------Y------- | | | | | | | | | | | | 411 chroma samples are sited like: YBR-----Y-------Y-------Y------- | | | | | | | | | | | | YBR-----Y-------Y-------Y------- | | | | | | | | | | | | YBR-----Y-------Y-------Y------- | | | | | | | | | | | | YBR-----Y-------Y-------Y------- | | | | | | | | | | | | We use a filter to resample at site locations one eighth pixel (at the source chroma plane's horizontal resolution) and five eighths of a pixel to the right. Then we use another filter to decimate the planes by 2 in the vertical direction.*/ static void y4m_convert_411_420jpeg(y4m_input *_y4m, unsigned char *_dst, unsigned char *_aux) { … } /*Convert 444 to 420jpeg.*/ static void y4m_convert_444_420jpeg(y4m_input *_y4m, unsigned char *_dst, unsigned char *_aux) { … } /*The image is padded with empty chroma components at 4:2:0.*/ static void y4m_convert_mono_420jpeg(y4m_input *_y4m, unsigned char *_dst, unsigned char *_aux) { … } /*No conversion function needed.*/ static void y4m_convert_null(y4m_input *_y4m, unsigned char *_dst, unsigned char *_aux) { … } static const char TAG[] = …; int y4m_input_open(y4m_input *y4m_ctx, FILE *file, char *skip_buffer, int num_skip, int only_420) { … } void y4m_input_close(y4m_input *_y4m) { … } int y4m_input_fetch_frame(y4m_input *_y4m, FILE *_fin, vpx_image_t *_img) { … }
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