Negative Scanning Instructions

Dale Callaham
Central Microscopy Facility
University of Massachusetts, Amherst, MA 01003



Instructions for Scanning Electron Microscopy Negatives

Remember to reserve the computer/scanner in the BCRC web-based reservation system!


Negative Scanning Notes.

 

1) For good quality and consistently exposed negatives it maybe possible to skip the preview and exposure adjustment steps, but with only an 8-bit data output range it can be difficult to get optimum exposure for all negatives without these steps.

 

2) The user should experiment with resolution settings and saved-file type in order to be sure that the digitized output will suit the need. When scanning as described above, the output might be (typ.) 4464x4032 pixels and 1.5Mb (as jpeg) for a 4" x 3.75" EM negative.  The files are large, even as JPGs, but this is necessary to capture all the details of an EM negative. If your purpose only requires a resolution such as you might see on the computer screen (of a whole negative), then a much lower resolution will suffice, and will yield a much smaller file: remember that the file size increases by the square of the linear resolution. But remember, the lower resolution image for web or PowerPoint  presentations can always be generated from the higher resolution image, but not the other way around. With the low cost of CD-R it makes sense to capture at full resolution, then put the negative away for safe keeping.

 

3) Saving as a JPG file compresses about 8-16x and ordinarily results in an image that is nearly indistinguishable from a tif image. Remember JPEG compression is "lossy", and does not purport to be able to perfectly restore the values or each pixel. Saving as a compressed TIFF image is another option. "jpeg-tiff" will essentially be a JPEG compression inside a TIFF image format. The usual "compressed-tiff" uses the LWZ compression engine and will faithfully reproduce the values of each pixel, but the output files are not as small as JPEGs and not as generally supported by imaging applications. Both compressed TIFF formats are supported by Photoshop, Corel, and some other high-end imaging programs, but not all image display utilities know how to read them.

 

4) The convention in the BCRC is to place your images in the "Users_temp" folder on the "Local Disk". Create a subdirectory named to a recognizable version of your user_name so that it can be known whose files these are.

 

5) Use Fetch or other file transfer program (find it in the "Recent Applications") to move the images off to a server. You can leave your image on the machine, but don't expect them to stay there for long!



Negative Scanning settings (BCRC - UMAX Astra2400s w\Transmission attachment and VueScan 7.6.84)

Input Tab: Select "More Options | All"
    Scan Task    Scan to File
    Scan From    Astra 2400s
    Scan Mode    Transparency
    Scan Quality    Archive
    Media Type    B/W negative
    Bits per Pixel    8 bit Gray
    Preview Res.    Auto.
    Scan Res.    600 dpi
    Auto Save    Scan
    # Passes    1

Output Tab: (Select "More Options | All")
    Printed Size    Scan Size
    Magnification    100%
    Output JPG file    (checked)
    JPEG Size Reduc    1
    JPEG Quality    90
    JPEG b/w    (checked)

600 dpi is the maximum resolution setting available now, and seems to work OK; this software doesn't show a 1200 dpi mode,  The exposure is much more reliable and easier than previous versions. Just preview and delineate the negative - it handles the dynamic range from clear base to high density areas. Go to 12 bit mode if you have extreme dynamic range.

If the system configuration changes, this may still be useful as a guide for negative scanning.