/*
 * jcsample.c
 *
 * Copyright (C) 1991-1994, Thomas G. Lane.
 * This file is part of the Independent JPEG Group's software.
 * For conditions of distribution and use, see the accompanying README file.
 *
 * This file contains downsampling routines.
 *
 * Downsampling input data is counted in "row groups".  A row group
 * is defined to be max_v_samp_factor pixel rows of each component,
 * from which the downsampler produces v_samp_factor sample rows.
 * A single row group is processed in each call to the downsampler module.
 *
 * The downsampler is responsible for edge-expansion of its output data
 * to fill an integral number of DCT blocks horizontally.  The source buffer
 * may be modified if it is helpful for this purpose (the source buffer is
 * allocated wide enough to correspond to the desired output width).
 * The caller (the prep controller) is responsible for vertical padding.
 *
 * The downsampler may request "context rows" by setting need_context_rows
 * during startup.  In this case, the input arrays will contain at least
 * one row group's worth of pixels above and below the passed-in data;
 * the caller will create dummy rows at image top and bottom by replicating
 * the first or last real pixel row.
 *
 * An excellent reference for image resampling is
 *   Digital Image Warping, George Wolberg, 1990.
 *   Pub. by IEEE Computer Society Press, Los Alamitos, CA. ISBN 0-8186-8944-7.
 *
 * The downsampling algorithm used here is a simple average of the source
 * pixels covered by the output pixel.  The hi-falutin sampling literature
 * refers to this as a "box filter".  In general the characteristics of a box
 * filter are not very good, but for the specific cases we normally use (1:1
 * and 2:1 ratios) the box is equivalent to a "triangle filter" which is not
 * nearly so bad.  If you intend to use other sampling ratios, you'd be well
 * advised to improve this code.
 *
 * A simple input-smoothing capability is provided.  This is mainly intended
 * for cleaning up color-dithered GIF input files (if you find it inadequate,
 * we suggest using an external filtering program such as pnmconvol).  When
 * enabled, each input pixel P is replaced by a weighted sum of itself and its
 * eight neighbors.  P's weight is 1-8*SF and each neighbor's weight is SF,
 * where SF = (smoothing_factor / 1024).
 * Currently, smoothing is only supported for 2h2v sampling factors.
 */

#define JPEG_INTERNALS
#include "jinclude.h"
#include "jpeglib.h"


/* Pointer to routine to downsample a single component */
typedef JMETHOD ( void, downsample1_ptr,
				  ( j_compress_ptr cinfo, jpeg_component_info * compptr,
					JSAMPARRAY input_data, JSAMPARRAY output_data ) );

/* Private subobject */

typedef struct {
	struct jpeg_downsampler pub; /* public fields */

	/* Downsampling method pointers, one per component */
	downsample1_ptr methods[MAX_COMPONENTS];
} my_downsampler;

typedef my_downsampler * my_downsample_ptr;


/*
 * Initialize for a downsampling pass.
 */

METHODDEF void
start_pass_downsample( j_compress_ptr cinfo ) {
	/* no work for now */
}


/*
 * Expand a component horizontally from width input_cols to width output_cols,
 * by duplicating the rightmost samples.
 */

LOCAL void
expand_right_edge( JSAMPARRAY image_data, int num_rows,
				   JDIMENSION input_cols, JDIMENSION output_cols ) {
	register JSAMPROW ptr;
	register JSAMPLE pixval;
	register int count;
	int row;
	int numcols = (int) ( output_cols - input_cols );

	if ( numcols > 0 ) {
		for ( row = 0; row < num_rows; row++ ) {
			ptr = image_data[row] + input_cols;
			pixval = ptr[-1]; /* don't need GETJSAMPLE() here */
			for ( count = numcols; count > 0; count-- )
				*ptr++ = pixval;
		}
	}
}


/*
 * Do downsampling for a whole row group (all components).
 *
 * In this version we simply downsample each component independently.
 */

METHODDEF void
sep_downsample( j_compress_ptr cinfo,
				JSAMPIMAGE input_buf, JDIMENSION in_row_index,
				JSAMPIMAGE output_buf, JDIMENSION out_row_group_index ) {
	my_downsample_ptr downsample = (my_downsample_ptr) cinfo->downsample;
	int ci;
	jpeg_component_info * compptr;
	JSAMPARRAY in_ptr, out_ptr;

	for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
		  ci++, compptr++ ) {
		in_ptr = input_buf[ci] + in_row_index;
		out_ptr = output_buf[ci] + ( out_row_group_index * compptr->v_samp_factor );
		( *downsample->methods[ci] )( cinfo, compptr, in_ptr, out_ptr );
	}
}


/*
 * Downsample pixel values of a single component.
 * One row group is processed per call.
 * This version handles arbitrary integral sampling ratios, without smoothing.
 * Note that this version is not actually used for customary sampling ratios.
 */

METHODDEF void
int_downsample( j_compress_ptr cinfo, jpeg_component_info * compptr,
				JSAMPARRAY input_data, JSAMPARRAY output_data ) {
	int inrow, outrow, h_expand, v_expand, numpix, numpix2, h, v;
	JDIMENSION outcol, outcol_h; /* outcol_h == outcol*h_expand */
	JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
	JSAMPROW inptr, outptr;
	INT32 outvalue;

	h_expand = cinfo->max_h_samp_factor / compptr->h_samp_factor;
	v_expand = cinfo->max_v_samp_factor / compptr->v_samp_factor;
	numpix = h_expand * v_expand;
	numpix2 = numpix / 2;

	/* Expand input data enough to let all the output samples be generated
	 * by the standard loop.  Special-casing padded output would be more
	 * efficient.
	 */
	expand_right_edge( input_data, cinfo->max_v_samp_factor,
					   cinfo->image_width, output_cols * h_expand );

	inrow = 0;
	for ( outrow = 0; outrow < compptr->v_samp_factor; outrow++ ) {
		outptr = output_data[outrow];
		for ( outcol = 0, outcol_h = 0; outcol < output_cols;
			  outcol++, outcol_h += h_expand ) {
			outvalue = 0;
			for ( v = 0; v < v_expand; v++ ) {
				inptr = input_data[inrow + v] + outcol_h;
				for ( h = 0; h < h_expand; h++ ) {
					outvalue += (INT32) GETJSAMPLE( *inptr++ );
				}
			}
			*outptr++ = (JSAMPLE) ( ( outvalue + numpix2 ) / numpix );
		}
		inrow += v_expand;
	}
}


/*
 * Downsample pixel values of a single component.
 * This version handles the special case of a full-size component,
 * without smoothing.
 */

METHODDEF void
fullsize_downsample( j_compress_ptr cinfo, jpeg_component_info * compptr,
					 JSAMPARRAY input_data, JSAMPARRAY output_data ) {
	/* Copy the data */
	jcopy_sample_rows( input_data, 0, output_data, 0,
					   cinfo->max_v_samp_factor, cinfo->image_width );
	/* Edge-expand */
	expand_right_edge( output_data, cinfo->max_v_samp_factor,
					   cinfo->image_width, compptr->width_in_blocks * DCTSIZE );
}


/*
 * Downsample pixel values of a single component.
 * This version handles the common case of 2:1 horizontal and 1:1 vertical,
 * without smoothing.
 *
 * A note about the "bias" calculations: when rounding fractional values to
 * integer, we do not want to always round 0.5 up to the next integer.
 * If we did that, we'd introduce a noticeable bias towards larger values.
 * Instead, this code is arranged so that 0.5 will be rounded up or down at
 * alternate pixel locations (a simple ordered dither pattern).
 */

METHODDEF void
h2v1_downsample( j_compress_ptr cinfo, jpeg_component_info * compptr,
				 JSAMPARRAY input_data, JSAMPARRAY output_data ) {
	int outrow;
	JDIMENSION outcol;
	JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
	register JSAMPROW inptr, outptr;
	register int bias;

	/* Expand input data enough to let all the output samples be generated
	 * by the standard loop.  Special-casing padded output would be more
	 * efficient.
	 */
	expand_right_edge( input_data, cinfo->max_v_samp_factor,
					   cinfo->image_width, output_cols * 2 );

	for ( outrow = 0; outrow < compptr->v_samp_factor; outrow++ ) {
		outptr = output_data[outrow];
		inptr = input_data[outrow];
		bias = 0;       /* bias = 0,1,0,1,... for successive samples */
		for ( outcol = 0; outcol < output_cols; outcol++ ) {
			*outptr++ = (JSAMPLE) ( ( GETJSAMPLE( *inptr ) + GETJSAMPLE( inptr[1] )
									  + bias ) >> 1 );
			bias ^= 1;  /* 0=>1, 1=>0 */
			inptr += 2;
		}
	}
}


/*
 * Downsample pixel values of a single component.
 * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
 * without smoothing.
 */

METHODDEF void
h2v2_downsample( j_compress_ptr cinfo, jpeg_component_info * compptr,
				 JSAMPARRAY input_data, JSAMPARRAY output_data ) {
	int inrow, outrow;
	JDIMENSION outcol;
	JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
	register JSAMPROW inptr0, inptr1, outptr;
	register int bias;

	/* Expand input data enough to let all the output samples be generated
	 * by the standard loop.  Special-casing padded output would be more
	 * efficient.
	 */
	expand_right_edge( input_data, cinfo->max_v_samp_factor,
					   cinfo->image_width, output_cols * 2 );

	inrow = 0;
	for ( outrow = 0; outrow < compptr->v_samp_factor; outrow++ ) {
		outptr = output_data[outrow];
		inptr0 = input_data[inrow];
		inptr1 = input_data[inrow + 1];
		bias = 1;       /* bias = 1,2,1,2,... for successive samples */
		for ( outcol = 0; outcol < output_cols; outcol++ ) {
			*outptr++ = (JSAMPLE) ( ( GETJSAMPLE( *inptr0 ) + GETJSAMPLE( inptr0[1] ) +
									  GETJSAMPLE( *inptr1 ) + GETJSAMPLE( inptr1[1] )
									  + bias ) >> 2 );
			bias ^= 3;  /* 1=>2, 2=>1 */
			inptr0 += 2; inptr1 += 2;
		}
		inrow += 2;
	}
}


#ifdef INPUT_SMOOTHING_SUPPORTED

/*
 * Downsample pixel values of a single component.
 * This version handles the standard case of 2:1 horizontal and 2:1 vertical,
 * with smoothing.  One row of context is required.
 */

METHODDEF void
h2v2_smooth_downsample( j_compress_ptr cinfo, jpeg_component_info * compptr,
						JSAMPARRAY input_data, JSAMPARRAY output_data ) {
	int inrow, outrow;
	JDIMENSION colctr;
	JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
	register JSAMPROW inptr0, inptr1, above_ptr, below_ptr, outptr;
	INT32 membersum, neighsum, memberscale, neighscale;

	/* Expand input data enough to let all the output samples be generated
	 * by the standard loop.  Special-casing padded output would be more
	 * efficient.
	 */
	expand_right_edge( input_data - 1, cinfo->max_v_samp_factor + 2,
					   cinfo->image_width, output_cols * 2 );

	/* We don't bother to form the individual "smoothed" input pixel values;
	 * we can directly compute the output which is the average of the four
	 * smoothed values.  Each of the four member pixels contributes a fraction
	 * (1-8*SF) to its own smoothed image and a fraction SF to each of the three
	 * other smoothed pixels, therefore a total fraction (1-5*SF)/4 to the final
	 * output.  The four corner-adjacent neighbor pixels contribute a fraction
	 * SF to just one smoothed pixel, or SF/4 to the final output; while the
	 * eight edge-adjacent neighbors contribute SF to each of two smoothed
	 * pixels, or SF/2 overall.  In order to use integer arithmetic, these
	 * factors are scaled by 2^16 = 65536.
	 * Also recall that SF = smoothing_factor / 1024.
	 */

	memberscale = 16384 - cinfo->smoothing_factor * 80; /* scaled (1-5*SF)/4 */
	neighscale = cinfo->smoothing_factor * 16; /* scaled SF/4 */

	inrow = 0;
	for ( outrow = 0; outrow < compptr->v_samp_factor; outrow++ ) {
		outptr = output_data[outrow];
		inptr0 = input_data[inrow];
		inptr1 = input_data[inrow + 1];
		above_ptr = input_data[inrow - 1];
		below_ptr = input_data[inrow + 2];

		/* Special case for first column: pretend column -1 is same as column 0 */
		membersum = GETJSAMPLE( *inptr0 ) + GETJSAMPLE( inptr0[1] ) +
					GETJSAMPLE( *inptr1 ) + GETJSAMPLE( inptr1[1] );
		neighsum = GETJSAMPLE( *above_ptr ) + GETJSAMPLE( above_ptr[1] ) +
				   GETJSAMPLE( *below_ptr ) + GETJSAMPLE( below_ptr[1] ) +
				   GETJSAMPLE( *inptr0 ) + GETJSAMPLE( inptr0[2] ) +
				   GETJSAMPLE( *inptr1 ) + GETJSAMPLE( inptr1[2] );
		neighsum += neighsum;
		neighsum += GETJSAMPLE( *above_ptr ) + GETJSAMPLE( above_ptr[2] ) +
					GETJSAMPLE( *below_ptr ) + GETJSAMPLE( below_ptr[2] );
		membersum = membersum * memberscale + neighsum * neighscale;
		*outptr++ = (JSAMPLE) ( ( membersum + 32768 ) >> 16 );
		inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;

		for ( colctr = output_cols - 2; colctr > 0; colctr-- ) {
			/* sum of pixels directly mapped to this output element */
			membersum = GETJSAMPLE( *inptr0 ) + GETJSAMPLE( inptr0[1] ) +
						GETJSAMPLE( *inptr1 ) + GETJSAMPLE( inptr1[1] );
			/* sum of edge-neighbor pixels */
			neighsum = GETJSAMPLE( *above_ptr ) + GETJSAMPLE( above_ptr[1] ) +
					   GETJSAMPLE( *below_ptr ) + GETJSAMPLE( below_ptr[1] ) +
					   GETJSAMPLE( inptr0[-1] ) + GETJSAMPLE( inptr0[2] ) +
					   GETJSAMPLE( inptr1[-1] ) + GETJSAMPLE( inptr1[2] );
			/* The edge-neighbors count twice as much as corner-neighbors */
			neighsum += neighsum;
			/* Add in the corner-neighbors */
			neighsum += GETJSAMPLE( above_ptr[-1] ) + GETJSAMPLE( above_ptr[2] ) +
						GETJSAMPLE( below_ptr[-1] ) + GETJSAMPLE( below_ptr[2] );
			/* form final output scaled up by 2^16 */
			membersum = membersum * memberscale + neighsum * neighscale;
			/* round, descale and output it */
			*outptr++ = (JSAMPLE) ( ( membersum + 32768 ) >> 16 );
			inptr0 += 2; inptr1 += 2; above_ptr += 2; below_ptr += 2;
		}

		/* Special case for last column */
		membersum = GETJSAMPLE( *inptr0 ) + GETJSAMPLE( inptr0[1] ) +
					GETJSAMPLE( *inptr1 ) + GETJSAMPLE( inptr1[1] );
		neighsum = GETJSAMPLE( *above_ptr ) + GETJSAMPLE( above_ptr[1] ) +
				   GETJSAMPLE( *below_ptr ) + GETJSAMPLE( below_ptr[1] ) +
				   GETJSAMPLE( inptr0[-1] ) + GETJSAMPLE( inptr0[1] ) +
				   GETJSAMPLE( inptr1[-1] ) + GETJSAMPLE( inptr1[1] );
		neighsum += neighsum;
		neighsum += GETJSAMPLE( above_ptr[-1] ) + GETJSAMPLE( above_ptr[1] ) +
					GETJSAMPLE( below_ptr[-1] ) + GETJSAMPLE( below_ptr[1] );
		membersum = membersum * memberscale + neighsum * neighscale;
		*outptr = (JSAMPLE) ( ( membersum + 32768 ) >> 16 );

		inrow += 2;
	}
}


/*
 * Downsample pixel values of a single component.
 * This version handles the special case of a full-size component,
 * with smoothing.  One row of context is required.
 */

METHODDEF void
fullsize_smooth_downsample( j_compress_ptr cinfo, jpeg_component_info *compptr,
							JSAMPARRAY input_data, JSAMPARRAY output_data ) {
	int outrow;
	JDIMENSION colctr;
	JDIMENSION output_cols = compptr->width_in_blocks * DCTSIZE;
	register JSAMPROW inptr, above_ptr, below_ptr, outptr;
	INT32 membersum, neighsum, memberscale, neighscale;
	int colsum, lastcolsum, nextcolsum;

	/* Expand input data enough to let all the output samples be generated
	 * by the standard loop.  Special-casing padded output would be more
	 * efficient.
	 */
	expand_right_edge( input_data - 1, cinfo->max_v_samp_factor + 2,
					   cinfo->image_width, output_cols );

	/* Each of the eight neighbor pixels contributes a fraction SF to the
	 * smoothed pixel, while the main pixel contributes (1-8*SF).  In order
	 * to use integer arithmetic, these factors are multiplied by 2^16 = 65536.
	 * Also recall that SF = smoothing_factor / 1024.
	 */

	memberscale = 65536L - cinfo->smoothing_factor * 512L; /* scaled 1-8*SF */
	neighscale = cinfo->smoothing_factor * 64; /* scaled SF */

	for ( outrow = 0; outrow < compptr->v_samp_factor; outrow++ ) {
		outptr = output_data[outrow];
		inptr = input_data[outrow];
		above_ptr = input_data[outrow - 1];
		below_ptr = input_data[outrow + 1];

		/* Special case for first column */
		colsum = GETJSAMPLE( *above_ptr++ ) + GETJSAMPLE( *below_ptr++ ) +
				 GETJSAMPLE( *inptr );
		membersum = GETJSAMPLE( *inptr++ );
		nextcolsum = GETJSAMPLE( *above_ptr ) + GETJSAMPLE( *below_ptr ) +
					 GETJSAMPLE( *inptr );
		neighsum = colsum + ( colsum - membersum ) + nextcolsum;
		membersum = membersum * memberscale + neighsum * neighscale;
		*outptr++ = (JSAMPLE) ( ( membersum + 32768 ) >> 16 );
		lastcolsum = colsum; colsum = nextcolsum;

		for ( colctr = output_cols - 2; colctr > 0; colctr-- ) {
			membersum = GETJSAMPLE( *inptr++ );
			above_ptr++; below_ptr++;
			nextcolsum = GETJSAMPLE( *above_ptr ) + GETJSAMPLE( *below_ptr ) +
						 GETJSAMPLE( *inptr );
			neighsum = lastcolsum + ( colsum - membersum ) + nextcolsum;
			membersum = membersum * memberscale + neighsum * neighscale;
			*outptr++ = (JSAMPLE) ( ( membersum + 32768 ) >> 16 );
			lastcolsum = colsum; colsum = nextcolsum;
		}

		/* Special case for last column */
		membersum = GETJSAMPLE( *inptr );
		neighsum = lastcolsum + ( colsum - membersum ) + colsum;
		membersum = membersum * memberscale + neighsum * neighscale;
		*outptr = (JSAMPLE) ( ( membersum + 32768 ) >> 16 );

	}
}

#endif /* INPUT_SMOOTHING_SUPPORTED */


/*
 * Module initialization routine for downsampling.
 * Note that we must select a routine for each component.
 */

GLOBAL void
jinit_downsampler( j_compress_ptr cinfo ) {
	my_downsample_ptr downsample;
	int ci;
	jpeg_component_info * compptr;
	boolean smoothok = TRUE;

	downsample = (my_downsample_ptr)
				( *cinfo->mem->alloc_small ) ( (j_common_ptr) cinfo, JPOOL_IMAGE,
											   SIZEOF( my_downsampler ) );
	cinfo->downsample = (struct jpeg_downsampler *) downsample;
	downsample->pub.start_pass = start_pass_downsample;
	downsample->pub.downsample = sep_downsample;
	downsample->pub.need_context_rows = FALSE;

	if ( cinfo->CCIR601_sampling ) {
		ERREXIT( cinfo, JERR_CCIR601_NOTIMPL );
	}

	/* Verify we can handle the sampling factors, and set up method pointers */
	for ( ci = 0, compptr = cinfo->comp_info; ci < cinfo->num_components;
		  ci++, compptr++ ) {
		if ( compptr->h_samp_factor == cinfo->max_h_samp_factor &&
			 compptr->v_samp_factor == cinfo->max_v_samp_factor ) {
#ifdef INPUT_SMOOTHING_SUPPORTED
			if ( cinfo->smoothing_factor ) {
				downsample->methods[ci] = fullsize_smooth_downsample;
				downsample->pub.need_context_rows = TRUE;
			} else
#endif
			downsample->methods[ci] = fullsize_downsample;
		} else if ( compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
					compptr->v_samp_factor == cinfo->max_v_samp_factor ) {
			smoothok = FALSE;
			downsample->methods[ci] = h2v1_downsample;
		} else if ( compptr->h_samp_factor * 2 == cinfo->max_h_samp_factor &&
					compptr->v_samp_factor * 2 == cinfo->max_v_samp_factor ) {
#ifdef INPUT_SMOOTHING_SUPPORTED
			if ( cinfo->smoothing_factor ) {
				downsample->methods[ci] = h2v2_smooth_downsample;
				downsample->pub.need_context_rows = TRUE;
			} else
#endif
			downsample->methods[ci] = h2v2_downsample;
		} else if ( ( cinfo->max_h_samp_factor % compptr->h_samp_factor ) == 0 &&
					( cinfo->max_v_samp_factor % compptr->v_samp_factor ) == 0 ) {
			smoothok = FALSE;
			downsample->methods[ci] = int_downsample;
		} else {
			ERREXIT( cinfo, JERR_FRACT_SAMPLE_NOTIMPL );
		}
	}

#ifdef INPUT_SMOOTHING_SUPPORTED
	if ( cinfo->smoothing_factor && !smoothok ) {
		TRACEMS( cinfo, 0, JTRC_SMOOTH_NOTIMPL );
	}
#endif
}
