AVIR

Introduction

Me, Aleksey Vaneev, is happy to offer you an open source image resizing library which has reached a production level of quality, and is ready to be incorporated into any project. This library features routines for both down- and upsizing of 8- and 16-bit, 1 to 4-channel images. Image resizing routines were implemented in multi-platform C++ code, and have a high level of optimality. Beside resizing, this library offers a sub-pixel shift operation.

The resizing algorithm at first produces 2X upsized image (relative to the source image size, or relative to the destination image size if downsizing is performed) and then performs interpolation using a bank of sinc function-based fractional delay filters. On the last stage a correction filter is applied which fixes smoothing introduced on previous steps.

An important element utilized by this algorithm is the so called Peaked Cosine window function, which is applied over sinc function in all filters. Please consult the documentation for more details.

Requirements

C++ compiler and system with efficient “float” floating point (24-bit mantissa) type support. This library can also internally use the “double” floating point type during resizing if needed. This library does not have dependencies beside the standard C library.

Links

• Documentation

Usage Information

The image resizer is represented by the avir::CImageResizer<> class, which is a single front-end class for the whole library. You do not basically need to use nor understand any other classes beside this class.

The code of the library resides in the “avir” C++ namespace, effectively isolating it from all other code. The code is thread-safe. You need just a single resizer object per running application, at any time, even when resizing images concurrently.

To resize images in your application, simply add 3 lines of code:

• include “avir.h”

• avir :: CImageResizer<> ImageResizer( 8 );
• ImageResizer.resizeImage( … ); (multi-threaded operation requires additional coding, see the documentation)

The library is able to process images of any bit depth: this includes 8-bit, 16-bit, float and double types. Larger integer and signed integer types are not supported. Supported source and destination image sizes are up to 2.1 gigapixels (46300x46300 or equivalent dimensions, e.g. 53467x40100).

The code of this library was commented in the Doxygen style. To generate the documentation locally you may run the “doxygen ./other/avirdoxy.txt” command from the library’s directory. Note that the code was suitably documented allowing you to make modifications, and to gain full understanding of the algorithm.

Preliminary tests show that this library can resize 8-bit RGB 5184x3456 (17.9 Mpixel) image down to 1037x691 (0.7 Mpixel) image in 380 milliseconds, utilizing a single thread, on a typical Intel Core i7-4770K processor-based system without overclocking. This scales down to 130 milliseconds if 4 threads are utilized. However, multi-threaded operation is not provided by this library “out of the box”. The multi-threaded infrastructure is fully available, but requires additional system-specific interfacing code for engagement.

Notes

This library was tested for compatibility with GNU C++, Microsoft Visual C++ and Intel C++ compilers, on 32- and 64-bit Windows, Mac OS X and CentOS Linux. The code was also tested with Dr.Memory/Win32 for the absence of uninitialized or unaddressable memory accesses.

All code is fully “inline”, without the need to compile any source files. The memory footprint of the library itself is very modest, except that the size of the temporary image buffers depends on the input and output image sizes, and is proportionally large.

The “heart” of resizing algorithm’s quality resides in the parameters defined via the avir::CImageResizerParams structure. While the default set of parameters that offers a good quality was already provided, there is still a place for improvement exists, and the default parameters may change in a future update. If you need to recall an exact set of parameters, simply save them locally for a later use.

This library includes binary command line tool “imageresize” for major desktop platforms. These binaries were designed to be used as a demonstration of library’s performance and as a reference. These binaries use the following libraries:

• turbojpeg Copyright (c) 2009-2013 D. R. Commander
• libpng Copyright (c) 1998-2013 Glenn Randers-Pehrson
• zlib Copyright (c) 1995-2013 Jean-loup Gailly and Mark Adler

Users

This library is used by:

Please drop me a note at aleksey.vaneev@gmail.com and I will include a link to your product to the list of users. This list is important at maintaining confidence in this library among the interested parties.