Pre-processing of big sizes even if original image is smaller

[BenjaminBrandmeier]

Pre-processing should only take place up to the size of the original image. After changing the script the viewer has to be adapted accordingly to pick only original images at a certain screen size.

[foto-andreas]

Cool project! Regarding this issue missing image resolutions should be accepted dynamically by the viewer. I'd like to provide only one or two resolutions, or only the raw size of the image. So many resolutions need much space. I resolved that by using the external url method.

One options, I changed manually in the source, would be cool to have as an attribute at the gallery element

preferredSize (currently fixed to auto)

But if one could set the wanted previews in the generator phase and the viewer would use only the sizes it finds, this would be obsolete.

Also an option --previewQuality for generation image previews.

[LeanderCoevoet]

Made a pull request for this:
#83