File sizes and Resampling Images

Certain Photoshop Filters such as Cutout, Chalk and Charcoal and Spatter require that the original photo image be resized to a smaller resolution. The optimum image size for digital photopainting is 4 megapixels (approx. 14" x 18" at 72 dpi). Unlike hi-end digital photography, the purpose behind digital photopainting is not to capture detail. It is instead to render essential detail and to simulate strokes and texture. Only after a photopainting is finished, we can resample images to a larger size, especially for printing purposes.

Photoshop uses five methods for image resampling: Nearest Neighbor, Bilinear, Bicubic, Bicubic Smoother, and Bicubic Sharper, the last two of which were introduced in Photoshop CS. You choose the one you want in the General panel of the Preferences dialog box or in the Image Size dialog box.

Bicubic interpolation creates better effects than Nearest Neighbor or Bilinear, with smoother tonal gradations.This resampling images method works by evaluating adjacent and nearby pixels and performing complex calculations on their values in order to predict what the pixel being worked on should be.

The bicubic method that Photoshop employs to scale up images work fine for digital photopainting because the surrounding pixels are closer in value than in photographic images and therefore there is less interpolation and errors.