| Author |
Message |
    
Anonymous
| | Posted on Tuesday, October 26, 1999 - 11:55 am: |   |
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John Strait
| | Posted on Tuesday, October 26, 1999 - 11:59 am: | |
The following discussion can serve as a starting point for your own thinking on this subject. I don't pretend to have a definitive answer to this one.
Most things I've read suggest that if you are intending to print the result, you should plan for a printed image resolution of 200-300dpi. That means that if you want prints that are about 4" high, you need originals somewhere around 1000-1500 pixels high (to allow for warping, cropping etc).
If you are scanning 35mm negatives or transparencies in portrait orientation I suggest scanning at 1000-1500 dpi for 4" high prints. More for larger prints. Even more if you feel you are not getting good sharpness at lower resolution.
The best idea is to start using the program and experiment. You will quickly determine what works best. |
Dave Reece
| | Posted on Tuesday, September 12, 2000 - 1:21 pm: | |
John,
Redo your math. A 35mm scan in portrait mode (1.5 inch high) should only require an 800dpi scan to achieve a 4 inch high print at 300dpi final output. Am I right or am I right?
-Dave |
John Strait
| | Posted on Tuesday, September 12, 2000 - 2:06 pm: | |
Hi Dave,
Your calculations are correct, but they only apply if you are printing full frame images without any image processing. I see now that I wasn't very clear about how I arrived at my original answer.
There are several factors that contribute to the need for higher scanning resolution.
First, the image warping that permits matching adjacent images produces a scalloping effect at the top and bottom of the final image. This robs you of some image height. See Why does the panoramic image have a curved top and bottom? for more on this scalloping effect.
Second, if you use spherical reprojection, the vertical scale is non-linear. This produces a further compression of the image height. See Cylindrical vs. Spherical Projection for more about spherical reprojection.
Third, there may be loss of sharpness when adjacent images are blended. See Image sharpness in stitched panoramas for more on this subject.
Finally, you may want to crop the image for composition. The panoramic stitcher requires that you keep your camera level. This often produces more sky or more foreground than you want in your final composition. So you must crop the image, removing more height.
I added 20% at the suggested minimum 1000 dpi for a margin of error to allow for these factors. Scanning at 1500 dpi for a 4 inch high print may be overly conservative, but you must be the judge of that.
I hope this helps explain my answer better! |
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