Archived posting to the Leica Users Group, 2003/07/17
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Clive Moss <chmphoto@sbcglobal.net> said: > Hmmm -- that is not what I thought. When I do print, I have been resizing > and resampling, then sharpening at the resampled resolution, viewing the > image on the screen at 1-1 pixel resolution. > > What should one do about sharpening if one does not resample? First, what is sharpening: The sharpening algorithm works by increasing the contrast at the borders between contrasting image regions. For example, if you have a region of light gray and a region of dark gray, with a sharp border between them, the sharpener will change some light gray pixels towards white, and some dark gray pixels towards black, right along the border. This makes the border "stand out" more strongly to our visual system. I have read/heard about two schools of thought about sharpening: 1) Sharpen after scanning. This would be done to counter any deficiencies in the scanner, that could "soften" the image. However, with any reasonable modern scanner, this probably isn't necessary. Some people may still sharpen after scanning because they think that the image looks better onscreen. Personally, I would not recommend sharpening after scanning. If you think about the sharpening algorithm as described above, all you are doing by sharpening at this step is just mucking up your data. 2) Sharpen before printing. This will create the perception of extra sharpness in the print. The sharpening should be done after the image has been resampled for the printer. If you are going to print two different sizes, say 8x10 and 16x20, you will sharpen separately for each print size. This is because the sharpening effect depends on both the _amount_ the local contrast is increased, and the _area_ it affects. If you are going to rely on your printer's driver to resample the image, then you will have to use trial-and-error to find the right sharpening settings. On-screen inspection on your computer's monitor will not be very useful. You must be careful when using sharpening. If you apply it too zealously, you can introduce unwanted artifacts in your image, like "ringing" effects along edges. You can also end up sharpening the film grain, which you probably don't want to do. I have seen some grossly oversharpened images that look super sharp at first glance, but look truly awful on closer inspection. btw: If you want to learn more about this kind of stuff, I highly recommended taking the course "Digital Printing for the Fine Art Photographer" offered through http://www.calypsoinc.com It is worth the price of admission just to learn about sharpening! later, Mike - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html