Change Image Size

Whereas you can usually scale down an image file without an issue, enlarging an image file can be problematic in terms of resolution. Therefore, make sure that when you enlarge images that you use the correct procedure and suitable software.

The scaling down of images, to reduce them in size to use, e.g., on the internet, is an option on almost every available image reading and image processing program. You can also use shareware for this purpose. Many programs provide excellent batch job options which allow you to easily reduce even large amounts of image content to the desired size. Further processing steps such as inserting watermarks, copyright notes and changes in colour or contrast can be completed in one step.

Programs

  • Irfanview
  • Faststone Imageviewer


Expanding or enlarging the image files is much more problematic (interpolation). In this instance, pixels are added without the program actually having actual image information, i.e. image details at hand. The programs calculate the additional pixels according to the information available in the original output image (interpolation). Interpolation of images to 200% of the original image with the right starting material (especially a low amount of image noise) and the right technique is relatively straight forward. However, no further image information can be added, instead only the image’s size is increased, avoiding further image interference (e.g. step-like formation becoming visible). This allows the image to be used in a larger format. In subject images that rely on richness of detail, the lack of image details can be become apparent when they are enlarged (e.g. detailed landscape photographs – see example images). The area of close range or portrait photography provides better conditions for enlarging images. Usually the viewing distance is larger and missing image details (e.g. pores) are not considered so much to be deficient in quality.


Methods to enlarge / Interpolation

To avoid a step-like formation from occurring, you should use the calculation method „bicubic interpolation“. This method is unfortunately not provided in every program that is free of charge. One disadvantage of this calculation method is that images can sometimes be slightly blurred. However, this deficit can be rectified by careful image sharpening. As well as the classic image processing programs such as, e.g., Photoshop, Photoshop Elements… there are also programs that are specialised in image enlarging. These programs sometimes also offer more elaborate algorithms for interpolation.

  • Photo zoom
  • Genuine Fractals

Both images were resized to 400% of their original size (Photoshop – Method – Bicubic interpolation) and then the focus was sharpened (Photoshop – Method – Unsharp masking). The quality of the landscape image is considerably lower than that of the portrait of the child. This is due to the fact that missing image information and poor resolution becomes much more noticeable in detailed image subjects when they are subsequently enlarged.

Resizing to 400%

Child’s portrait – Cuba 2008
Child's portrait – Cuba 2008

 

Resizing to 400%

Landscape with palm trees and the sea – Cuba – 2008
Landscape with palm trees and the sea – Cuba – 2008
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