This is with reference to a comment made about the images under: Gallery>Astrophotography by Bert van Winsen "Considering that the images have been compressed significantly, the jpeg artifacts are not too bad"
I have noticed that different jpg compression algorithms, such as the Lancoz and Bicubic filters give final images of differing quality. I wonder if there is a quick explanation as to what each of these interpolation modes are optimised for. Have tried to scan the net, but not much luck with a straight-forward answer.
Regards,
The reason I'm asking is because whenever I convert a graphic to JPG, there is invariably an option to select one of a range of filters or compression algorithms. It would be very useful to know if there is a preferred filter for JPGs with a lot of text in them. Or what about high contrast JPGs like images of bright galaxies with inky black backgrounds? There are a host of filters on various software pacakges. The Bicubic and Lancoz are defaults on two packages I use most often (Photoshop and ACDSee), which is why I wanted to know if, on these grounds alone, these filters are optimized for certain images.
The discussion goes on (with reference to Bert van Winsen's image of M8 in the Gallery):
"albert": I assumed the "blotchiness", particularly around all the stars, were jpeg artifacts, resulting in poor star definition in this image, because this is absent from my original image. Perhaps it is something else, like a scaling artifact? I see the same problem cropping up in Percy's images (his Eagle Nebula).
"groess": those JPG artifacts might very well be introduced by the DotNetNuke engine which drives the website. I seem to think it has its own resizing algorithm, which is perhaps best suited to images of aunt Betty on the beach!
"albert": I was able to simulate the effect in the simple act of scaling the image down to 500 pixels in width (using bicubic default or smoother; bicubic sharper makes the problem worse). So I conclude that it is probably a scaling effect. Maybe this type of discussion should be on the forum?