Entries by category: Scanning glass plates


Resolving the image

As discussed in last week's post we have recently made important decisions on the Holtermann Collection digitisation standards. Although the library already has an established set of digitisation guidelines new considerations needed to be made for such an important and high quality collection of glass plate negatives along with the introduction of our new glass plate scanner.

We did not take this process lightly and so began by researching the digitisation practices and standards of our fellow cultural institutions, most notably the National Information Standards Organisation of America, National Government Archives of America and the National Library of Australia. We also looked at glass plate digitisation case studies, such as the Wellcome Library's John Thompson collection, to get a feel for the workflows and technical specifications used by other world class institutions.

Based on this gathered information we determined to perform a series of test scans in three different pixel dimensions (approximately 5 000, 7500 and 10000 pixels in length) to see how much detail the Holtermann negatives really hold and how well we could capture it. We performed these tests using the scanner's true optical resolution to ensure that no pixel interpolation occurred. This means the actual pixel dimension is closer to 11000 pixels and can vary slightly because the glass plates are not all exactly the same size. Below is an image we selected for test scanning due to it's high level of detail and sharpness showing the detail sections of the tests.

Once we saw the truly impressive amount of information stored in these negatives we were determined to save archival master files to our highest test scan resolution of approximately 10000 pixels on the longest edge creating a 450MB, uncompressed, 16 bit, Adobe 1998 RGB TIF file from each plate. Including our 8 bit, Gray Gamma 2.2 sub-master file derivatives that's nearly 3 terabytes of total storage space needed in total.


It's all in the detail

It's been a productive last few weeks on the project. In this time we've agreed upon and implemented a digitisation standard to encompass the entire 3,500 strong collection. We will be posting some more technical details on the process we used to make these important decisions during the next few weeks. For now, let's have a look at the implications of our new high quality digitisation standard in layman's terms.

Part of our decision making process was to create a series of test scans using different scanner settings and file sizes. The results were astounding! Because the Holtermann negatives were created using the wet-collodion or wet plate process they are virtually grain free. In short, this means that their resolution is only limited by the quality of the camera lens the negative was exposed with, so we are able to pick out tiny details in the negative and bring them up clearly. In the picture below of the gold rush town of Gulgong, NSW for example;

This image had previously been batch scanned from the corresponding 35mm copy negative, so we had a basic idea of what was in the image. Unfortunately, details such as text in signs and the items in shop windows were not distinguishable. Until, that is, we rescanned the original glass plate negative on our new scanner. Below is an enlarged section from the original 35mm copy negative scan (left) and our new scan (right) - you can see the amazing difference in detail retention the high quality scan is giving us.

Every word on the poster is clearly visible. Not only that, the costume and accessories of the time - such as the pipe and hats in this image - have become much easier to examine. What fantastic implications for historians and future researchers of the gold rush era in Victoria and New South Wales!

Family historians will also be able to gain an insight to their gold rush ancestors never before possible with clear close up views of those amazing faces available. A great example is this gentleman outside Stafford Henry Barnes' Mudgee Drug Store in Gulgong, NSW;

We would love to hear your thoughts on our progress so far.

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Join our discussions about this exciting project to digitise 3,500 glass plate negatives documenting the 1870s gold rush era in New South Wales and Victoria.

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