Restoration of Delaminated and Cracked Recordings Using Synthetic - PowerPoint PPT Presentation

Restoration of Delaminated and Cracked Recordings Using Synthetic Depth of Field

Optical Scanning of Disc Recordings

IRENE 2D Setup

Delamination on Lacquer Discs Image source: [1]

A Closer Look

Ways to Handle Cracks ● Crack detection (S. Fischer [2]) Detect crack with displacement sensor – Rescan the blurred area – Works well for small number of radial cracks – ● Synthetic depth of field Acquire a stack of subscans with different height offsets – Merge the subscans – Image source: [3]

Questions to be Answered ● Spacing of the scans? Determine depth of field of the current system – ● How can sharp regions be detected? Focus measures – Which is the right one for this application? – ● How can the images be efficiently fused? Size of one image 300 MB - 800 MB –

Depth of Field How can the relevant depth of field for the audio extraction be determined? DoF = λ 0 n n Microscopy theory: 2 + M NA e ≈ 38 μ m NA Problem: that does not tell us anything about how the depth of field affects the audio

Depth of Field Experimental approach: ● Scan a silent portion of the groove ● Extracted audio contains only noise ● Change focus plane ● Signal RMS can be used as noise measure

Depth of Field Just notable difference ~ 1 dB [4] => 40 μm spacing

Depth of Field Z-offset 0 um Z-offset +40 um

Acquisition System Before: Tracking New: Focus Stacking

Image stack

Outlook ● Currently working on the image fusion algorithm

Sources [1] Northeast Document Conservation Center. IRENE Seeing Sound Blog. A Hefty Challenge for IRENE: Working with Delaminating Lacquer Discs, August 2014. https://www.nedcc.org/audio-preservation/irene-blog/ [03/14/2015]. [2] S. Fischer. Restoring Cracked Early Recordings. Master’s thesis, Zurich University of Applied Sciences, September 2013. [3] M. M. Karim. Focus stacking Tachinid fly. March 2009. http://commons.wikimedia.org/wiki/File:Focus_stacking_Tachinid_fly.jpg [05/31/2015] [4] Wikipedia. Just-noticeable difference. http://en.wikipedia.org/wiki/Just-noticeable_difference [06/04/2015].

Perpendicular Lighting

Processing Steps