Scanning slabs for Bubble Counter
The scanner must have an optical resolution of at least 3,175 dpi to meet the ASTM C457 requirements for discriminating an air void of 10 microns diameter. 3,175 dpi yields a pixel size of 8 microns and results in very large tif files.
This procedure assumes slabs have been treated so as to maximize the contrast between air voids and solids and that there are stickers placed at strategic locations such that the surface of the slab does not come into contact with the glass scanner platen.
- With a soft brush, sweep the surface of the scanner platen gathering all of the dust into one of the bottom corners of the scanner platen.
- Place the white card on the top side of the platen and place the slab just below it.
- Open the scanning software, ScanWizard in the case of the Microtek scanner in the lab and preview the scanning area.
- Insure that the scan resolution is set to 3,175 dpi and that all post-processing filters are disabled.
- Select a scan area encompassing all of the slab and all or part of the white card. In order to minimize the size of the scanned image, keep the area scanned to a minimum. Only a portion of the white balance card that includes both black and white samples is required.
- Scan the image to a grayscale tif (again to minimize image size - a color tif will be three times the size of a grayscale and all of the color information is discarded during analysis).