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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
This commit is contained in:
Hermet Park 2019-05-13 15:45:50 +09:00
parent 9d28d91626
commit 7ef58f9581
1 changed files with 69 additions and 32 deletions
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101
src/modules/evas/image_loaders/png/evas_image_load_png.c
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@ -230,7 +230,6 @@ 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;
@ -382,7 +381,7 @@ 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)
{
@ -396,6 +395,7 @@ 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)
@ -406,51 +406,86 @@ 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))
png_read_row(png_ptr, tmp_line, NULL);
src_ptr = 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];
dst_ptr += pack_offset;
src_ptr += (scale_ratio * pack_offset);
for (j = 1; j < w; j++)
{
DATA32 *dst_ptr = (DATA32 *) surface;
DATA32 *src_ptr2;
//rgba
interp_buf[0] = 0;
interp_buf[1] = 0;
interp_buf[2] = 0;
interp_buf[3] = 0;
for (i = 0; i < h; i++)
//horizontal interpolation.
for (p = 0; p < scale_ratio; p++)
{
png_read_row(png_ptr, tmp_line, NULL);
src_ptr2 = (DATA32 *) (tmp_line + region_x * pack_offset);
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);
for (k = 0; k < (int) pack_offset; k++)
interp_buf[k] += src_ptr[k - (int)(p * pack_offset)];
}
}
else
{
unsigned char *dst_ptr = surface;
for (k = 0; k < (int) pack_offset; k++)
dst_ptr[k] = (interp_buf[k] / scale_ratio);
for (i = 0; i < h; i++)
dst_ptr += pack_offset;
src_ptr += (scale_ratio * pack_offset);
}
//next lines
for (i = 1; i < h; i++)
{
memset(interp_buf, 0x00, line_size * sizeof(unsigned short));
//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);
}
}
@ -459,6 +494,8 @@ 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)