Add ability to save RGBA image as TIFF with associated-alpha (premultiplied) transparency channel.

[william@…]

At the moment, GIL cannot save an image with an "A" channel to a TIFF file. This patch adds this ability.

I added "GIL" as a keyword, since there's still no "GIL" component in the drop-down list.

[william@…]

Patch which adds ability to save alpha channel as premultiplied alpha in TIFF file.

[john.femiani@…]

You can not read TIFF images with alpha either.

I posted something to the mailing list: ​http://lists.boost.org/boost-users/2008/08/39259.php

[john.femiani@…]

A testcase for reading rgba

[john.femiani@…]

A file to use with the testcase I attached

[john.femiani@…]

I could not attach the dang patch, "Akismet" says it is spam.

Here is is cut-and-pasted into the wiki:

png_io_private.hpp

@@ -291 +291 @@
             default: io_error("png_reader_color_convert::apply(): unknown combination of color type and bit depth"); 
             } 
             break; 
+ case PNG_COLOR_TYPE_PALETTE: 
+ io_error("png_reader_color_convert::apply(): cannot read png images with a pallette (yet)"); 
+ 
         default: io_error("png_reader_color_convert::apply(): unknown color type"); 
         } 
         png_read_end(_png_ptr,NULL); 

tiff_dynamic_io.hpp

@@ -56 +56 @@
 class tiff_type_format_checker { 
     int _bit_depth; 
     int _color_type; 
+ unsigned short _samples_per_pixel; 
 public: 
- tiff_type_format_checker(int bit_depth_in,int color_type_in) : 
- _bit_depth(bit_depth_in),_color_type(color_type_in) {} 
+ tiff_type_format_checker( int bit_depth_in 
+ , int color_type_in 
+ , unsigned short samples_per_pixel_in 
+ ) 
+ : _bit_depth(bit_depth_in) 
+ , _color_type(color_type_in) 
+ , _samples_per_pixel(samples_per_pixel_in) 
+ {} 
     template <typename Image> 
     bool apply() { 
- return tiff_read_support<typename Image::view_t>::bit_depth==_bit_depth && 
- tiff_read_support<typename Image::view_t>::color_type==_color_type; 
+ typedef tiff_read_support<typename Image::view_t> traits; 
+ 
+ int my_samples_per_pixel = size<typename Image::value_type>(); 
+ 
+ bool same_bit_depth = traits::bit_depth == _bit_depth; 
+ bool same_color_type = traits::color_type == _color_type; 
+ bool same_samples_per_pixel = my_samples_per_pixel == _samples_per_pixel; 
+ 
+ bool result = same_bit_depth && same_color_type; 
+ 
+ if (_samples_per_pixel) 
+ result = result && same_samples_per_pixel; 
+ 
+ return result; 
     } 
 }; 
  
@@ -77 +96 @@
  
     template <typename Images> 
     void read_image(any_image<Images>& im) { 
- int width,height; 
- unsigned short bps,photometric; 
- TIFFGetField(_tp,TIFFTAG_IMAGEWIDTH,&width); 
- TIFFGetField(_tp,TIFFTAG_IMAGELENGTH,&height); 
- TIFFGetField(_tp,TIFFTAG_BITSPERSAMPLE,&bps); 
- TIFFGetField(_tp,TIFFTAG_PHOTOMETRIC,&photometric); 
- if (!construct_matched(im,tiff_type_format_checker(bps,photometric))) { 
+ int width; 
+ int height; 
+ unsigned short bps=1; 
+ unsigned short photometric = 1; 
+ unsigned short samples_per_pixel = 0; 
+ TIFFGetField(_tp, TIFFTAG_IMAGEWIDTH, &width); 
+ TIFFGetField(_tp, TIFFTAG_IMAGELENGTH, &height); 
+ TIFFGetField(_tp, TIFFTAG_BITSPERSAMPLE,&bps); 
+ TIFFGetField(_tp, TIFFTAG_PHOTOMETRIC, &photometric); 
+ TIFFGetField(_tp, TIFFTAG_SAMPLESPERPIXEL, &samples_per_pixel); 
+ if (!construct_matched(im, tiff_type_format_checker(bps,photometric, samples_per_pixel))) { 
             io_error("tiff_reader_dynamic::read_image(): no matching image type between those of the given any_image and that of the file"); 
         } else { 
             im.recreate(width,height); 

tiff_io.hpp

@@ -1 +1 @@
 /* 
     Copyright 2005-2007 Adobe Systems Incorporated 
- 
+ 
     Use, modification and distribution are subject to the Boost Software License, 
     Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at 
     http://www.boost.org/LICENSE_1_0.txt). 
@@ -51 +51 @@
     BOOST_STATIC_CONSTANT(int,color_type=PHOTOMETRIC_RGB); 
 }; 
 template <> 
+struct tiff_read_support_private<bits8,rgba_t> { 
+ BOOST_STATIC_CONSTANT(bool,is_supported=true); 
+ BOOST_STATIC_CONSTANT(int,bit_depth=8); 
+ BOOST_STATIC_CONSTANT(int,color_type=PHOTOMETRIC_RGB); 
+}; 
+template <> 
 struct tiff_read_support_private<bits16,gray_t> { 
     BOOST_STATIC_CONSTANT(bool,is_supported=true); 
     BOOST_STATIC_CONSTANT(int,bit_depth=16); 
@@ -94 +100 @@
     BOOST_STATIC_CONSTANT(int,color_type=PHOTOMETRIC_RGB); 
 }; 
 template <> 
+struct tiff_write_support_private<bits8,rgba_t> { 
+ BOOST_STATIC_CONSTANT(bool,is_supported=true); 
+ BOOST_STATIC_CONSTANT(int,bit_depth=8); 
+ BOOST_STATIC_CONSTANT(int,color_type=PHOTOMETRIC_RGB); 
+}; 
+template <> 
 struct tiff_write_support_private<bits16,gray_t> { 
     BOOST_STATIC_CONSTANT(bool,is_supported=true); 
     BOOST_STATIC_CONSTANT(int,bit_depth=16); 
@@ -129 +141 @@
     ~tiff_reader() { TIFFClose(_tp); } 
     template <typename View> 
     void apply(const View& view) { 
- unsigned short bps,photometric; 
+ unsigned short bps,spp, photometric; 
         point2<std::ptrdiff_t> dims=get_dimensions(); 
         io_error_if(TIFFGetField(_tp,TIFFTAG_BITSPERSAMPLE,&bps)!=1); 
         io_error_if(TIFFGetField(_tp,TIFFTAG_PHOTOMETRIC,&photometric)!=1); 
+ io_error_if(TIFFGetField(_tp,TIFFTAG_SAMPLESPERPIXEL,&spp)!=1); 
         io_error_if(dims!=view.dimensions(), 
                     "tiff_read_view: input view size does not match TIFF file size"); 
         io_error_if(tiff_read_support_private<typename channel_type<View>::type, 
                                               typename color_space_type<View>::type>::bit_depth!=bps || 
                     tiff_read_support_private<typename channel_type<View>::type, 
- typename color_space_type<View>::type>::color_type!=photometric, 
+ typename color_space_type<View>::type>::color_type!=photometric || 
+ mpl::size<typename color_space_type<View>::type>::value != spp, 
                     "tiff_read_view: input view type is incompatible with the image type"); 
         std::size_t element_size=sizeof(pixel<typename channel_type<View>::type, 
                                               layout<typename color_space_type<View>::type> >); 
@@ -166 +180 @@
 }; 
  
 // This code will be simplified... 
-template <typename CC> 
+template <typename CC> 
 class tiff_reader_color_convert : public tiff_reader { 
 private: 
     CC _cc; 
 public: 
- tiff_reader_color_convert(const char* filename) : 
+ tiff_reader_color_convert(const char* filename) : 
         tiff_reader(filename) {} 
- tiff_reader_color_convert(const char* filename,CC cc_in) : 
+ tiff_reader_color_convert(const char* filename,CC cc_in) : 
         tiff_reader(filename),_cc(cc_in) {} 
     template <typename View> 
     void apply(const View& view) { 
@@ -273 +287 @@
         default: { 
             // reads an image in incompatible format via TIFFReadRGBAImage 
             rgba8_image_t rgbaImg(dims); 
- io_error_if(!TIFFReadRGBAImage(_tp, dims.x, dims.y, (uint32*)&gil::view(rgbaImg)(0,0), 0), 
+ io_error_if(!TIFFReadRGBAImage(_tp, dims.x, dims.y, (uint32*)&gil::view(rgbaImg)(0,0), 0), 
                 "tiff_reader_color_convert::unsupported image format"); 
             copy_and_convert_pixels(flipped_up_down_view(const_view(rgbaImg)), view, _cc); 
         } 
@@ -353 +367 @@
 /// \ingroup TIFF_IO 
 /// \brief Loads the image specified by the given tiff image file name into the given view. 
 /// Triggers a compile assert if the view color space and channel depth are not supported by the TIFF library or by the I/O extension. 
-/// Throws std::ios_base::failure if the file is not a valid TIFF file, or if its color space or channel depth are not 
+/// Throws std::ios_base::failure if the file is not a valid TIFF file, or if its color space or channel depth are not 
 /// compatible with the ones specified by View, or if its dimensions don't match the ones of the view. 
 template <typename View> 
 inline void tiff_read_view(const char* filename,const View& view) { 
@@ -372 +386 @@
 /// \ingroup TIFF_IO 
 /// \brief Allocates a new image whose dimensions are determined by the given tiff image file, and loads the pixels into it. 
 /// Triggers a compile assert if the image color space or channel depth are not supported by the TIFF library or by the I/O extension. 
-/// Throws std::ios_base::failure if the file is not a valid TIFF file, or if its color space or channel depth are not 
+/// Throws std::ios_base::failure if the file is not a valid TIFF file, or if its color space or channel depth are not 
 /// compatible with the ones specified by Image 
 template <typename Image> 
 void tiff_read_image(const char* filename,Image& im) {

[chhenning]

Please ise the new io extension. It provides you with all the features asked for in this ticket.