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preserve alpha channel in PNG, when imread(..., -1) is called (ticket #1107)

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This commit is contained in:
Vadim Pisarevsky 2011-08-11 22:38:09 +00:00
parent 6942799669
commit c65c67eff4
1 changed files with 24 additions and 12 deletions
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36
modules/highgui/src/grfmt_png.cpp
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@ -167,9 +167,18 @@ bool PngDecoder::readHeader()
if( bit_depth <= 8 || bit_depth == 16 )
{
m_type = color_type == PNG_COLOR_TYPE_RGB ||
color_type == PNG_COLOR_TYPE_RGB_ALPHA ||
color_type == PNG_COLOR_TYPE_PALETTE ? CV_8UC3 : CV_8UC1;
switch(color_type)
{
case PNG_COLOR_TYPE_RGB:
case PNG_COLOR_TYPE_PALETTE:
m_type = CV_8UC3;
break;
case PNG_COLOR_TYPE_RGB_ALPHA:
m_type = CV_8UC4;
break;
default:
m_type = CV_8UC1;
}
if( bit_depth == 16 )
m_type = CV_MAKETYPE(CV_16U, CV_MAT_CN(m_type));
result = true;
@ -210,15 +219,18 @@ bool PngDecoder::readData( Mat& img )
else if( !isBigEndian() )
png_set_swap( png_ptr );
/* observation: png_read_image() writes 400 bytes beyond
* end of data when reading a 400x118 color png
* "mpplus_sand.png". OpenCV crashes even with demo
* programs. Looking at the loaded image I'd say we get 4
* bytes per pixel instead of 3 bytes per pixel. Test
* indicate that it is a good idea to always ask for
* stripping alpha.. 18.11.2004 Axel Walthelm
*/
png_set_strip_alpha( png_ptr );
if(img.channels() < 4)
{
/* observation: png_read_image() writes 400 bytes beyond
* end of data when reading a 400x118 color png
* "mpplus_sand.png". OpenCV crashes even with demo
* programs. Looking at the loaded image I'd say we get 4
* bytes per pixel instead of 3 bytes per pixel. Test
* indicate that it is a good idea to always ask for
* stripping alpha.. 18.11.2004 Axel Walthelm
*/
png_set_strip_alpha( png_ptr );
}
if( m_color_type == PNG_COLOR_TYPE_PALETTE )
png_set_palette_to_rgb( png_ptr );