Fortunately you can now use SmillaEnlarger, a very simple tool that enlarges images while keeping quality loss at a minimum. How does it manage to do that? Easy: by apply a quick resizing algorithm – created by the developer - that smoothes and de-noises the original image.
SmillaEnlarger features a simple interface, though it can be a bit confusing to use. There are two preview windows, one with the complete image and the other one with the area currently under the zoom grid. You only have to resize this grid by dragging it with the mouse to make the image larger. Use the 'Preview' button to check the results, and the 'Calculate' button to save the image in the selected directory.
The only thing you should bear in mind is that the first result you obtain may not be the best one – that is, it may look too artificial, almost like an oil painting. My advice is to fiddle with all the available sliders (sharpness, flatness, presharpen, dithering and de-noise) and try different combinations until you find the perfect mixture of size and quality.
With SmillaEnlarger you can enlarge images without losing too much quality, and obtain a pretty decent big sized picture instead of a bunch of blurry pixels.
SmillaEnlarger supports the following formats
JPG, PNG, BMP, PPM, TIFF, GIF