Scanning old photographs question

The rows are one half pixel offset, to get in between. That one claims 2400dpi

They're one half photosite offset, not half a pixel. A pixel only exists after the photosite data are processed.

 

So from the photosite geometry shown, it would be possible to extrapolate 2400 pixels per inch, but only in one axis. The vertical axis can only support 1200 ppi because the photosites are asymmetrical and rectangular in shape and spacing. Therefore the vertical pixel value must be interpolated between two offset rows of photosites.

 

The overall pixel accuracy also depends on near absolute mechanical placement of the subject relative to the sensor, or vice-versa. Requiring a stepping accuracy of less than 2 microns x whatever the magnification ratio is.

 

so a funny spatial frequency response dip,

but you already said that doesn't bother you.

All pixelated images have a 'funny' spatial frequency response. The pixels' spacing varies depending on their angle relative to orthogonal. At 45 degrees, for example, the pixel spacing is 1.4 x that at 0 and 90 degrees.

 

I never said that the spatial frequency response 'doesn't bother me'. But as long as it's high enough, and at a sufficient amplitude for the intended purpose of the image, then why worry about it?

Edited July 27, 2020 by rodeo_joe|1

They're one half photosite offset, not half a pixel. A pixel only exists after the photosite data are processed.

 

So from the photosite geometry shown, it would be possible to extrapolate 2400 pixels per inch, but only in one axis. The vertical axis can only support 1200 ppi because the photosites are asymmetrical and rectangular in shape and spacing. Therefore the vertical pixel value must be interpolated between two offset rows of photosites.

 

The overall pixel accuracy also depends on near absolute mechanical placement of the subject relative to the sensor, or vice-versa. Requiring a stepping accuracy of less than 2 microns x whatever the magnification ratio is.

 

 

All pixelated images have a 'funny' spatial frequency response. The pixels' spacing varies depending on their angle relative to orthogonal. At 45 degrees, for example, the pixel spacing is 1.4 x that at 0 and 90 degrees.

 

I never said that the spatial frequency response 'doesn't bother me'. But as long as it's high enough, and at a sufficient amplitude for the intended purpose of the image, then why worry about it?

 

They could make it more obvious.

The whole array is 42.8mm long, with 10700 pixels (what they say) with 4um pitch.

I thought it was 4um along the array axis, but am not so sure now.

OK, so 2.4um wide cells on 4um centers.

 

Then there is the cylindrical lens, I believe over each of the six rows.

I think that narrows the effective height, but it doesn't explain that part.

 

Scanners are supposed to scan with increments smaller than the cell size, though with plastic

bands that might stretch moving the mirrors around.

 

I used to read comp.dsp where audio signal processing was a common discussion topic.

Frequency response is very important in audio.

 

Give the MTF graphs for film, it does seem that photography isn't so interested in it.

The response of the wider cells might not be so far from the MTF graphs that

go down to 10% or so.

I used to read comp.dsp where audio signal processing was a common discussion topic.

Frequency response is very important in audio.

Ah, OK.

That's a different kettle of bananas.

Audio sampling is essentially one-dimensional and ideally at a single point, or over a very small time-period, per sample.

 

Whereas image spatial sampling is 2 dimensional by necessity, both in sample area and as a re-assembled data matrix.

 

Ideally those sample areas would tesselate with no space in between, and it's this that the microlenses attempt to simulate. The actual photosites need space in between for electrical interconnects.

I still have a Nikon Coolscan V dedicated 35mm negative/slide scanner, but it only still works because of Vuescan since Nikon abandoned their software. You would think that even with film as a niche product that Nikon could make a steady profit by providing quality scanning of 35mm. Apparently not. I don't use film much these days but it's nice to have as long as it lasts. Most old pictures that I have scanned in I've used my Epson Perfection V500 because what negatives I had were large (and it was mostly prints). Epson did a good job with that scanning. I scanned all my Dad's family pictures to show to my relatives. Alas I only got them when my dad died so I couldn't really ask him about them.