Upsize

UPSIZE: An image upsizing plugin featuring two modes.
1. Smooth (IBFNBQH): Image upsizing with Interpolatory Box Filtered Natural BiQuadratic Histosplines. [This is the default option.]
2. Sharp (EANBQH): Exact Area image upsizing with Natural BiQuadratic Histosplines.

This plugin was written by Nicolas Robidoux and Adam Turcotte at Laurentian University in Sudbury, Ontario, Canada.

LAST UPDATED: March 25, 2011
The Smooth/Sharp radio buttons were not allowing Sharp to be used, so this has been fixed. Also, the plugin now uses gimp_image_insert_layer() for Gimp 2.7 and newer instead of gimp_image_add_layer(), which has been deprecated.

Note: This is a refined version of the code that was used to create the HQ_Rescale plugin for Windows (http://registry.gimp.org/node/13187).

For more details regarding these methods, see Fast Exact Area Image Upsampling with Natural Biquadratic Histosplines by Nicolas Robidoux, Adam Turcotte, Minglun Gong and Annie Tousignant, pp.85-96 of Image Analysis and Recognition, 5th International Conference, ICIAR 2008, Póvoa de Varzim, Portugal, June 25-27, 2008. Proceedings, Aurelio C. Campilho, Mohamed S. Kamel (Eds.). Lecture Notes in Computer Science 5112, Springer 2008, ISBN 978-3-540-69811-1. Only the "Sharp" version is explicitly discussed; "Smooth" differs in that it is box filtered (and in that this implementation uses a different image size convention than the "Sharp" resampler).

EANBQH Standalone Programs (Added: May 11, 2012)
Upsize Sharp has been implemented as a pair of standalone C programs:
eanbqh8 allows for PPM input images with 8-bit samples (maxval=255)
eanbqh16 allows for PPM input images with 16-bit samples (maxval=65535)
See the README file in eanbqh.tar.gz for more information.