Vuescan appears to be using "nearest neighbour" for downsampling

[mendel_leisk]

Just a heads-up, Vuescan appears to be using "nearest neighbour" for

downsampling, when used in the scan-from-disk process. At least the

result is similar to that process as done through Photoshop.

 

During scan-from-disk within Vuescan, downsampling is accomplished by

setting "Input|Scan(Preview) Resolution" to "Custom", and then

setting a number. In my case, I worked with raw files having dpi set

to 5400. By setting the custom dpi to 4000 during scan-from-disk, I

downsampled by 4000/5400.

 

Unfortunately, I've gotten a fair way into my project now, when I

happened to try a bi-cubic downsample of the raw file, through

Photoshop. Zooming both to 200%, serious "jaggies" are evident in the

Vuescan result, whlle Photoshop's bicubic output is much smoother.

 

Groan!

[bill_tuthill]

Odd, because Vueprint used to have (still has?) excellent resampling

algorithms. Did Ed Hamrick ever respond to e-mail about this issue?

[mendel_leisk]

Hi Bill,

<p>

Just noticed your post, hope you will notice my belated reply. Ed Hamrick is reported (Google's scanner forum) to have been asked this. His response was that it was sort of like bi-linear.

<p>

My experience with Vuescan downsampling was that it "broke up" into jaggie lines, very plainly at 200%. PS bi-cubic, on the other hand, stayed smooth. Perhaps it depends on the ratio you're downsampling. In my case, it was always the same: 4000/5400.

<p>

I discussed this also over in <a href="http://groups-beta.google.com/group/comp.periphs.scanners/browse_thread/thread/ae007c1258f0cfc5/4d24b3ce230fcbae">Google's scanner forum</a>.

[emre]

That's plain dumb. Can't he just borrow some code from ImageMagick to implement a better resampling algorithm? I would not resize in Vuescan until then.