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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 (

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.

GIMP Version: 
Code License: 


... I'm pretty sure that the 16-bit version of the C filter (that run independently of GIMP) is broken. I'm talking about eanbqh.tar.gz above.
Adam and I will not fix it: better things to do.

For some reason whatever I try, the image just looks like a regular bilinear filtered image, nothing better :(

Am I doing anything wrong?

I don't know if it works with 2.8.

I should look very different (it's more obvious when you enlarge a small image a lot), and when you switch between "smooth" and "sharp", the alignment of the enlargement should be different.

I have installed this app, but can't find it in Gimp. I've refreshed the scripts with script-fu, but I can't find it in the menus. Would it not make sense to explain on this page where it goes in the menu system, so new users can find it?



You can follow the changes in this plugin here:


here is the new Version for Mac. As before, it should be universal:

@Adam: Can you write a Version Number in the Plugin Window?


Thank you for the new Mac version. I have updated the file listing.

Also, thank you for the version number suggestion. I will add this to the next revision.

Adam Turcotte

Thanks; been using the older set that Photocomix passed on to me. Just deleted those and added this single plugin in its place. :)


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