Reducing and Enlarging Images

Resize v.s. Resample?
Today’s Photo Tip: Always Use Resampling to Reduce Image Size. When reducing (or enlarging) a photo, should you resize or resample it? In simple terms, resampling uses various algorithms, while resizing does not. As a result, resampling produces much smoother photos, while simple resizing may eliminate thin lines and produce some pixel steps in the image. The most common algorithm used to reduce photos is bilinear; while the most common algorithm used to enlarge photos is bicubic. Resampling only works on images with 24-bit color definition (16 million colors). The good news is that all JPGs are 24 bit color depth images. NOTE: Another common algorithm is the Lanczos filter, that compared with other filters, provides  (with a = 2) the "best compromise in terms of reduction of aliasing, sharpness, and minimal ringing", and when used (with a =3)  "it keeps low frequencies and rejects high frequencies better than any (achievable) filter previously available" and should be the default choice whenever possible.
 
For best results always check the "keep proportions" check box for the best results. If this box is checked you only need to give the new width in pixels and the height that keeps the proportions of the image will be automatically calculated or vice-versa. Often you will also be able to choose a percentage for the size reduction instead of a width/height in pixels. Often you will also be able to choose a percentage for the size reduction instead of a width/height in pixels. If needed, try using the “unsharp mask filter” to help sharpen the image.
 
What does all this mean? Why even perform resampling in the first place? To reduce file size for emailing and web posting. As an example, selecting reduce by 50% using the Lanczos3 filter, I recently resampled 24 pictures using the “batch convert” feature in FastStone Image Viewer. This process only took a matter of minutes and reduced the total file storage for all 24 images from 69MB to 11.8MB. Even with this huge reduction in file size, there was almost no visible difference when viewed on the computer screen. NOTE: Always save the ‘resampled’ images to a new folder. That way when you are done with your emailing or uploading to your web or blog site, you can simply delete the folder, leaving the originals intact. To read more on resampling, open the "Editing Pics" tab and scroll down to Step #7 ... Editing Pics.