evas png: apply interpolation when scale down image loading.

Summary:
This patch improves png quality when image uses scale-down at image loading.

Since current scale-down logic just works like point sampling,
image result could be wholely different,

Simply, if source data is consist of continous white and black pixels,
and scale down factor is 2, the sampled data would be only white,
and lose all black pixels, or vice versa.

The result can be unexpected by users.
Even current jpeg scale-down works with interpolation.

Before:
{F3711651}

After:
{F3711652}

Original:
{F3711653}

Reviewers: cedric, raster, #committers, kimcinoo, jsuya

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D8788

Change-Id: I904ace4bfe944e76beb4818af43f6bc63077c163

diff --git a/src/modules/evas/image_loaders/png/evas_image_load_png.c b/src/modules/evas/image_loaders/png/evas_image_load_png.c
index db8fb50..6d0c1e9 100644 (file)
--- a/src/modules/evas/image_loaders/png/evas_image_load_png.c
+++ b/src/modules/evas/image_loaders/png/evas_image_load_png.c
@@ -259,7 +259,6 @@ evas_image_load_file_data_png(void *loader_data,
    Eina_File *f;
 
    unsigned char *surface;
-   unsigned char *tmp_line;
    png_structp png_ptr = NULL;
    png_infop info_ptr = NULL;
    Evas_PNG_Info epi;
@@ -414,7 +413,7 @@ evas_image_load_file_data_png(void *loader_data,
      }
 
    passes = png_set_interlace_handling(png_ptr);
-   
+
    /* we read image line by line if scale down was set */
    if (scale_ratio == 1 && region_set == 0)
      {
@@ -428,6 +427,7 @@ evas_image_load_file_data_png(void *loader_data,
    else
      {
         unsigned char *src_ptr;
+        unsigned char *dst_ptr = surface;
         int skip_row = 0, region_x = 0, region_y = 0;
 
         if (region_set)
@@ -438,51 +438,86 @@ evas_image_load_file_data_png(void *loader_data,
 
         if (passes == 1)
           {
-             tmp_line = (unsigned char *) alloca(image_w * pack_offset);
+             int line_size = (image_w * pack_offset) - (region_x * pack_offset);
+             unsigned char *tmp_line = (unsigned char *) alloca(image_w * pack_offset);
+             //accumulate pixel color here.
+             unsigned short *interp_buf = (unsigned short *) alloca(line_size * sizeof(unsigned short));
+             unsigned short *pbuf;
 
              for (skip_row = 0; skip_row < region_y; skip_row++)
                png_read_row(png_ptr, tmp_line, NULL);
 
-             //general case: 4 bytes pixel.
-             if (pack_offset == sizeof(DATA32))
-               {
-                  DATA32 *dst_ptr = (DATA32 *) surface;
-                  DATA32 *src_ptr2;
+             png_read_row(png_ptr, tmp_line, NULL);
+             src_ptr = tmp_line + (region_x * pack_offset);
 
-                  for (i = 0; i < h; i++)
-                    {
-                       png_read_row(png_ptr, tmp_line, NULL);
-                       src_ptr2 = (DATA32 *) (tmp_line + region_x * pack_offset);
+             //The first pixel, of the first line
+             for (k = 0; k < (int) pack_offset; k++)
+               dst_ptr[k] = src_ptr[k];
 
-                       for (j = 0; j < w; j++)
-                         {
-                            *dst_ptr = *src_ptr2;
-                            ++dst_ptr;
-                            src_ptr2 += scale_ratio;
-                         }
-                       for (j = 0; j < (scale_ratio - 1); j++)
-                         png_read_row(png_ptr, tmp_line, NULL);
+             dst_ptr += pack_offset;
+             src_ptr += (scale_ratio * pack_offset);
+
+             for (j = 1; j < w; j++)
+               {
+                  //rgba
+                  interp_buf[0] = 0;
+                  interp_buf[1] = 0;
+                  interp_buf[2] = 0;
+                  interp_buf[3] = 0;
+
+                  //horizontal interpolation.
+                  for (p = 0; p < scale_ratio; p++)
+                    {
+                       for (k = 0; k < (int) pack_offset; k++)
+                         interp_buf[k] += src_ptr[k - (int)(p * pack_offset)];
                     }
+                  for (k = 0; k < (int) pack_offset; k++)
+                    dst_ptr[k] = (interp_buf[k] / scale_ratio);
+
+                  dst_ptr += pack_offset;
+                  src_ptr += (scale_ratio * pack_offset);
                }
-             else
+
+             //next lines
+             for (i = 1; i < h; i++)
                {
-                  unsigned char *dst_ptr = surface;
+                  memset(interp_buf, 0x00, line_size * sizeof(unsigned short));
 
-                  for (i = 0; i < h; i++)
+                  //vertical interpolation.
+                  for (j = 0; j < scale_ratio; j++)
                     {
                        png_read_row(png_ptr, tmp_line, NULL);
-                       src_ptr = tmp_line + region_x * pack_offset;
+                       src_ptr = tmp_line + (region_x * pack_offset);
 
-                       for (j = 0; j < w; j++)
+                      for (p = 0; p < line_size; ++p)
+                         interp_buf[p] += src_ptr[p];
+                    }
+
+                  for (p = 0; p < line_size; ++p)
+                    interp_buf[p] /= scale_ratio;
+
+                  pbuf = interp_buf;
+
+                  //The first pixel of the current line
+                  for (k = 0; k < (int) pack_offset; k++)
+                    dst_ptr[k] = pbuf[k];
+
+                  dst_ptr += pack_offset;
+                  pbuf += scale_ratio * pack_offset;
+
+                  for (j = 1; j < w; j++)
+                    {
+                       //horizontal interpolation.
+                       for (p = 1; p < scale_ratio; ++p)
                          {
                             for (k = 0; k < (int) pack_offset; k++)
-                              dst_ptr[k] = src_ptr[k];
-
-                            dst_ptr += pack_offset;
-                            src_ptr += scale_ratio * pack_offset;
+                              pbuf[k] += pbuf[k - (int)(p * pack_offset)];
                          }
-                       for (j = 0; j < (scale_ratio - 1); j++)
-                         png_read_row(png_ptr, tmp_line, NULL);
+                       for (k = 0; k < (int) pack_offset; k++)
+                         dst_ptr[k] = (pbuf[k] / scale_ratio);
+
+                       dst_ptr += pack_offset;
+                       pbuf += (scale_ratio * pack_offset);
                     }
                }
 
@@ -491,6 +526,8 @@ evas_image_load_file_data_png(void *loader_data,
           }
         else
           {
+             //TODO: Scale-down interpolation for multi-pass?
+
              unsigned char *pixels2 = malloc(image_w * image_h * pack_offset);
 
              if (pixels2)