/*

* jcsample.c

*

* Copyright (C) 1991-1996, 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];

/* Height of an output row group for each component. */

int rowgroup_height[MAX_COMPONENTS];

/* These arrays save pixel expansion factors so that int_downsample need not

* recompute them each time. They are unused for other downsampling methods.

*/

UINT8 h_expand[MAX_COMPONENTS];

UINT8 v_expand[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 * downsample->rowgroup_height[ci]);

(*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)

{

my_downsample_ptr downsample = (my_downsample_ptr) cinfo->downsample;

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 * compptr->DCT_h_scaled_size;

JSAMPROW inptr, outptr;

INT32 outvalue;

h_expand = downsample->h_expand[compptr->component_index];

v_expand = downsample->v_expand[compptr->component_index];

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 = outrow = 0;

while (inrow < cinfo->max_v_samp_factor) {

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;

outrow++;

}

}

/*

* 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 * compptr->DCT_h_scaled_size);

}

/*

* 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 inrow;

JDIMENSION outcol;

JDIMENSION output_cols = compptr->width_in_blocks * compptr->DCT_h_scaled_size;

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 (inrow = 0; inrow < cinfo->max_v_samp_factor; inrow++) {

outptr = output_data[inrow];

inptr = input_data[inrow];

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 * compptr->DCT_h_scaled_size;

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 = outrow = 0;

while (inrow < cinfo->max_v_samp_factor) {

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;

outrow++;

}

}

#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 * compptr->DCT_h_scaled_size;

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 = outrow = 0;

while (inrow < cinfo->max_v_samp_factor) {

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;

outrow++;

}

}

/*

* 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 inrow;

JDIMENSION colctr;

JDIMENSION output_cols = compptr->width_in_blocks * compptr->DCT_h_scaled_size;

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 (inrow = 0; inrow < cinfo->max_v_samp_factor; inrow++) {

outptr = output_data[inrow];

inptr = input_data[inrow];

above_ptr = input_data[inrow-1];

below_ptr = input_data[inrow+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;

int h_in_group, v_in_group, h_out_group, v_out_group;

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++) {

/* Compute size of an "output group" for DCT scaling. This many samples

* are to be converted from max_h_samp_factor * max_v_samp_factor pixels.

*/

h_out_group = (compptr->h_samp_factor * compptr->DCT_h_scaled_size) /

cinfo->min_DCT_h_scaled_size;

v_out_group = (compptr->v_samp_factor * compptr->DCT_v_scaled_size) /

cinfo->min_DCT_v_scaled_size;

h_in_group = cinfo->max_h_samp_factor;

v_in_group = cinfo->max_v_samp_factor;

downsample->rowgroup_height[ci] = v_out_group; /* save for use later */

if (h_in_group == h_out_group && v_in_group == v_out_group) {

#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 (h_in_group == h_out_group * 2 &&

v_in_group == v_out_group) {

smoothok = FALSE;

downsample->methods[ci] = h2v1_downsample;

} else if (h_in_group == h_out_group * 2 &&

v_in_group == v_out_group * 2) {

#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 ((h_in_group % h_out_group) == 0 &&

(v_in_group % v_out_group) == 0) {

smoothok = FALSE;

downsample->methods[ci] = int_downsample;

downsample->h_expand[ci] = (UINT8) (h_in_group / h_out_group);

downsample->v_expand[ci] = (UINT8) (v_in_group / v_out_group);

} else

ERREXIT(cinfo, JERR_FRACT_SAMPLE_NOTIMPL);

}

#ifdef INPUT_SMOOTHING_SUPPORTED

if (cinfo->smoothing_factor && !smoothok)

TRACEMS(cinfo, 0, JTRC_SMOOTH_NOTIMPL);

#endif

}