  Recognition of document images have important applications in restoring old
and classical texts. The problem involves quality improvement before passing it
to a properly trained OCR to get accurate recognition of the text. The image
enhancement and quality improvement constitute important steps as subsequent
recognition depends upon the quality of the input image. There are scenarios
when high resolution images are not available and our experiments show that the
OCR accuracy reduces significantly with decrease in the spatial resolution of
document images. Thus the only option is to improve the resolution of such
document images. The goal is to construct a high resolution image, given a
single low resolution binary image, which constitutes the problem of single
image super-resolution. Most of the previous work in super-resolution deal with
natural images which have more information-content than the document images.
Here, we use Convolution Neural Network to learn the mapping between low and
the corresponding high resolution images. We experiment with different number
of layers, parameter settings and non-linear functions to build a fast
end-to-end framework for document image super-resolution. Our proposed model
shows a very good PSNR improvement of about 4 dB on 75 dpi Tamil images,
resulting in a 3 % improvement of word level accuracy by the OCR. It takes less
time than the recent sparse based natural image super-resolution technique,
making it useful for real-time document recognition applications.
