Some people eat, sleep and chew gum, I do genealogy and write...

Wednesday, December 13, 2017

How important is high resolution for scanning and photography?

Are you tempted to join the megapixel race? Are you concerned about the resolution of your digitization efforts for photos, paper records, and other genealogically important documents? Do you use the megapixel count of a camera or smartphone as a factor in your purchase decisions? These issues and more concern anyone trying to digitize records or take photographs. Genealogists and photographers share some of the same concerns.

I have written on this topic several times in the past. Here is a list of some past posts that deal with aspects of this topic:
This list could go on and on. In a recent post, I expressed my views on the challenges of genealogy and I included an issue about the unrealistic digital resolution and file format requirements imposed by those engineers and administrators of online collections thereby increasing inability of the larger collections to ingest smaller collections of records. On reflection, that topic needs more explanation and discussion. 

In response to my post on the challenges to genealogy, I got the following comment:
I have always been a believer that preservation should be performed at the highest possible resolution. As time has passed, as you mention, this could be 50 Megapixels today, and who know how much tomorrow? But the biggest advantage of 50 vs 12 Megapixels is the ability to zoom in and examine details closely. I have found this very helpful with things like scans of old vital records where correct interpretation of handwriting, for example, requires great magnification. It is useless if zooming in only results in a highly pixelated image. This applies likewise to photographs where the only image of GG Grandpa is a tiny section of a larger image. If I want to recognize his features clearly, I am grateful for a 50 Meg scan. Obviously, as you mention, file size (storage capacity) is an issue, but less so as time passes. Therefore, I support the ". . . unrealistic digital resolution and file format requirements imposed by those engineers and administrators of online collections . . .". Tomorrow's researchers will thank us for adhering to those high standards.
Is there a direct relationship with a high megapixel count, say 50 megapixels or more, and the ability to recognize small features in either a photograph or another type of document?

We need to start any discussion of this type with some observations about physical reality.

I will start with photographs. Analog photographs using photographic film are considered to be continuous tone images. However, the resolution of a photograph depends on the type of film used. The sensitivity of film to light is measured in a number assigned by the International Organization for Standardization or ISO or the American Standards Association, now known as the American National Standards Insitute, or ANSI whose standard is usually designated by the older acronym, ASA number. There is a direct relationship between a film's ISO/ASA number and its ability to resolve fine detail, i.e. resolution. The higher the ISO/ASA number, the larger the grains of light-sensitive material, usually some compound of silver, used to capture the image. These numbers are usually used to represent the "speed" of the film or the time it takes to form an image. The higher the numbers, say around 1000 or 2000, mean that the film is very "fast." The tradeoff is always a loss in detail i.e. graininess of the image.

There is no free lunch, greater resolution means smaller discrete light sensitive elements. Photographers know that high ISO/ASA numbers (or fast film) mean a decline in detail in direct proportion to the additional speed. For those wishing to digitally reproduce film photographs, the resolution of the copy cannot exceed the original. Any document or photograph has a certain limit of resolution. Once a duplication method reaches that point of resolution there is no more information in the original that will be lost because of the copy. It may seem counterintuitive, but higher resolution scanning or photography past a certain threshold will simply result in larger file sizes and not any more detail. Once that limit has been reached, there is no more information to obtain.

I am not here talking about photographs of real-life objects, I am talking about copying historical records and photographs, essentially digital reproductions of actual analog documents.

Here is an example of what I mean. This is a microfilmed copy of a record from the website that was previously microfilmed and has now been made available in a digitized copy:

Now, how did this image come to be on the website? In a simplified explanation, someone had access to the original record and then made a photographic copy of the original using some type of microfilm. Here, the resolution was determined by the type of film, probably with a very low ISO/ASA number below 100, i.e. with the highest amount of detail available. Now, to move this image into the digital world, FamilySearch made a digital image at some extremely high resolution (for a digital image) and then processed that image for display on its website. What about the resolution of this image? Well, first of all, it is a JPEG image and we will have to view the image on our computer's monitor. Let's see what happens to this image at magnification. Here is a screenshot of the image at 300%.

Hmm. there appear to be some problems with the original. There is a great deal of bleed through from the back of the page. What about higher resolution? Here it is again at 600%.

Is there an upper limit? Yes, here is the image is again at 800%:

At this point, further magnification will simply start more pixelation and not provide any more detail. Could this be extended indefinitely be making the original with a higher digital pixel count? In reality, the file size would increase dramatically but you would still be limited by the resolution of the original image. Here is the same image at 1200% magnification.

Any higher and the image will start to become unrecognizable. Where can you see the most detail? Guess what? That depends on how closely you look at the image. If you stand some distance back, the high magnification images look just like the ones with lower magnification.

There is a reason why the Libray of Congress established standards as set forth in its "Guidelines: Technical Guidelines for Digitizing Cultural Heritage Materials." There is a balance between increased resolution and the preservation of the detail in a document or photograph. Higher resolutions give you larger file sizes but at some point, no more information from the original.

There is no free lunch. You cannot beat the system and the system is physics.

1 comment:

  1. Right on!
    There are other concerns too. What it’s viewed on, how it’s transmitted or stored. The software involved in rendering and reading is important to.