Camera scanning: conservator's perspective

**Oren Grad** · 17-Jun-2019, 13:53

Originally Posted by rdeloe

I didn't want to muddy the water in my original post, but that source I mentioned addresses this topic too for those who want a brief overview. Peterson distinguishes "Object Reproduction" (Preservation Digital Object), "Content Reproduction" (easy readable, looks good) and "Speculative Artist's Intention". The last one is particularly interesting in that the conservationist is trying to show the image the way the artist intended it to be viewed, which is obviously a tricky game.

To which I'll add that I appreciate your launching this thread. The various conservation perspectives offer a nice framework for thinking more clearly about decisions we need to make in our respective practices, and bring useful insights that are often missing from the seemingly endless wrangling, largely out of context, over input and output resolutions.

**Photomagica** · 4-Aug-2019, 23:06

Museum professionals typically work to standards, as mentioned in this thread. Understanding the goals one is trying to achieve and establishing a standard to meets those goals consistently is key to efficient, high quality, professional work.
The Harvard DASCH Scanner for astronomical plates may be of interest. https://arxiv.org/ftp/astro-ph/papers/0610/0610351.pdf
The paper descries how DASCH was put together - essentially a cam-scanner on steroids. This scanner was built a number of years ago and continues to be used for a great deal of critical work. For example plates from a number of observatories were measured with DASCH to assist in improving calculations of the orbit of Pluto so the New Horizons probe would not miss.
This scanner operates at 2311.6 DPI and the astronomers designing it consider this sufficient, after analysis and now a great deal of experience, to "capture all of the information on a photographic plate". The scanner data consistently yields a far better analysis, called a plate reduction, than a human operator working at a manual measuring engine. DASCH digitizes a 14x17 plate in 92 seconds. It has been used to digitize hundred of thousands of plates. We may be critical of the astronomer's goal of 2311.6 DPI, however they have proven it is sufficient for essentially all research purposes, so this has proved to be an excellent standard for astronomical plates.
Bill Peters
Astronomical Consultant and Museum Professional

**Pere Casals** · 5-Aug-2019, 03:15

Originally Posted by rdeloe

The last one is particularly interesting in that the conservationist is trying to show the image the way the artist intended it to be viewed, which is obviously a tricky game.

I'd like to add that scanning is only a share, digital post processing is also very important.

In the far future it will be prossible to take a 1 MPix image for each grain

but by now we can only have a few pixels for each large grain, and less than one pixel for one small grain.

IMHO priority is to capture the grain structure as it would be shown in the print. Prints don't show all grains perfectly, with focus accuracy, with lens/paper performance and with diffuser vs condenser, grain nature on the print varies, and then we have the print enlargement effect.

In the same way the grain nature varies in the digital image depending on digital processing, we probably will apply several sharpening actions one after the other to optimize different concepts in the image... then when we resize the image...

Regarding the capture, DSLR scanners are a good solution because we benefit from the expensive development for a mass production product, but linear sensors are still a better solution ...anyway in the DIY realm controlling a linear camera or interfacing a sensor is not as easy as triggering a DSLR.

Problem we have now is that EPSON has near a monopoly for sheets, the V800 is a 2006 product with a LED illumination that probably is cheaper, we also see a better holder, but in 14 years that product had not changed substantially.

We have to be grateful because we still have a very able device that it can be purchased new and that it has drivers for modern computers, but if they had competition and a larger market to allow investments then we would see more improvements.