Views
767
Replies
11
Status
Closed
Graphics amateur here, but I stumbled across something which is probably old hat to you pros. However, I’d like to share it with the class and see what you lot think about it…
I’m currently agonizing over scanning resolution and bit-depth to use to scan irreplaceable family photos, negatives and slides. The idea was to use optical maximums for archiving and then, at a later date, possibly scale down for printing and displaying, as required.
However, 48-bit color at 2400 dpi produces obscenely huge files so I devised a little test to see how accurate those specs really are.
I scanned an image twice in succession. A binary comparison of the two files revealed them to be quite different. And it doesn’t matter what resolution or color depth I used. Even 1-bit, 50 dpi scans come out different!?
Puzzled, I exported the images as RAW and wrote a quick-and-dirty program to average them out. I used 5 scans, added up values for each pixel and then divided by 5 producing a simple "average" image. This is a very pedestrian, plain-vanilla algorithm for data acquisition, I didn’t even bother eliminating the extremes.
(BTW, how do I average images in PS 6.0.1? I played with Apply image and Blending modes but I just can’t produce the desired effect. It’s all those options. Brain hurts…)
Anyway, back to my "average" image. Instead of improving things, this actually made matters worse as the resulting image came out "soft" and out of focus.
So, I wrote another little quick-and-dirty "difference" routine to compare two images like so: if file 1 pixel < file 2 pixel I assigned it a value of 255 ("white"), if file 1 pixel > 2 it became a 0 ("black"), and if both are same the resulting pixel became 127 ("gray"). Once I loaded this "difference image" it looked like it was put through an emboss filter and it had R, G & B "shadows" indicating both vertical and horizontal displacement.
(Again, how would I produce such a "difference image" in PS 6.0.1?)
Anyway, this means not only are room-temperature CCDs quite inaccurate but stepper motor tolerances appear quite bad too.
Sure makes me wonder about all those "generous" bit-depth and resolution claims, and puts my agonizing over them into perspective.
Don.
I’m currently agonizing over scanning resolution and bit-depth to use to scan irreplaceable family photos, negatives and slides. The idea was to use optical maximums for archiving and then, at a later date, possibly scale down for printing and displaying, as required.
However, 48-bit color at 2400 dpi produces obscenely huge files so I devised a little test to see how accurate those specs really are.
I scanned an image twice in succession. A binary comparison of the two files revealed them to be quite different. And it doesn’t matter what resolution or color depth I used. Even 1-bit, 50 dpi scans come out different!?
Puzzled, I exported the images as RAW and wrote a quick-and-dirty program to average them out. I used 5 scans, added up values for each pixel and then divided by 5 producing a simple "average" image. This is a very pedestrian, plain-vanilla algorithm for data acquisition, I didn’t even bother eliminating the extremes.
(BTW, how do I average images in PS 6.0.1? I played with Apply image and Blending modes but I just can’t produce the desired effect. It’s all those options. Brain hurts…)
Anyway, back to my "average" image. Instead of improving things, this actually made matters worse as the resulting image came out "soft" and out of focus.
So, I wrote another little quick-and-dirty "difference" routine to compare two images like so: if file 1 pixel < file 2 pixel I assigned it a value of 255 ("white"), if file 1 pixel > 2 it became a 0 ("black"), and if both are same the resulting pixel became 127 ("gray"). Once I loaded this "difference image" it looked like it was put through an emboss filter and it had R, G & B "shadows" indicating both vertical and horizontal displacement.
(Again, how would I produce such a "difference image" in PS 6.0.1?)
Anyway, this means not only are room-temperature CCDs quite inaccurate but stepper motor tolerances appear quite bad too.
Sure makes me wonder about all those "generous" bit-depth and resolution claims, and puts my agonizing over them into perspective.
Don.
Related Tags
Master Retouching Hair
Learn how to rescue details, remove flyaways, add volume, and enhance the definition of hair in any photo. We break down every tool and technique in Photoshop to get picture-perfect hair, every time.