Bug fixes:

• Imager::Test::is_imaged() attempted to process an "epsilon" parameter but the prototype didn't allow for the extra parameter. Corrected the prototype.
• when downconverting samples (eg. from floating point to 8 bit) Imager now rounds the sample value rather than attempting to allocate input values over output values equally. The old behaviour had the probably surprising effect of converting a floating point 2.1/255.0 into an 8-bit 3 rather than the expected 2. This may result in slightly different 8 or 16-bit output images.
• BI_BITFIELD BMP images were handled incorrectly, both in incorrectly calculating the space required for the masks and in processing the image data itself. RT #76736
• some odd width BMP BI_RLE4 images use run lengths that run one off the edge of the image. Imager now allows this, discarding the extra column.
• odd length RLE4 runs in BMP images were decoded incorrectly.
• pkg-config could sometimes return a library that was in a directory EU::MM / $Config{libpth} doesn't know about, but the compiler did. If no -L is included in the pkg-config library information check if EU::MM can find the library, and if not, search our configured directories and insert that into the library flags. RT #75869
• Imager::Probe can now probe for libraries with dependent libraries, common for static linking, eg. libpng requires libz. RT #74043
• libpng 1.5 specific probes were looking for libpng 1.4 filenames.
• added alternative probe configurations that try to link libz, to handle a statically linked libpng. RT #74043
• if a probe includes testcode, Imager::Probe now checks that code as part of the process of checking each configuration rather than as a post test of the found configuration. This allows alternate configurations to be checked if a matching but non-working configuration is found. RT 74043

Other changes:

• when reading or writing images via callbacks, the default callbacks now push an error message indicating that a required callback was called but not supplied. RT #76782
• clarify which callbacks are required for reading and writing TIFF images.
• improve logging for creation of callback I/O layers.
• a little more documentation for Imager::Probe.
• the i_get_file_background() and i_get_file_backgroundf() APIs now return int to indicate whether the i_background tag was found.

PNG rework

• improve error reporting
• add png_interlace, png_bits tags
• read paletted images as paletted images, including transparency
• read 1 bit greyscale images as a type suitable for other file handlers to write as bilevel
• read 16 bit/sample PNG as 16-bit/sample Imager images
• write "bilevel" paletted images as 1 bit grayscale images
• write paletted images as paletted images
• write 16-bit (or higher)/sample images as 16-bit/sample PNG images
• improved metadata support

RT #29268