On Fri, 18 May 2007 05:29:52 GMT, Dennis Lee Bieber <bieber.genealogy@earthlink.net> wrote: >On Thu, 17 May 2007 20:26:29 -0800, Vampire Slayer ><Don'tHaveOne@nowhere.net> declaimed the following in >soc.genealogy.misc: > > >> >> I also usually scan documents at 300 dpi. Depending on what the >> original looks like I'll do gray scale if it is black and white and >> color if it is either in color or detail can be seen better in color. >> Unless it's a pristine printed page I've found that black & white >> scanning usually loses a lot of detail. >> >> I normally scan photo's at 600 dpi. That seems to be the sweet spot >> for me on quality versus file size. Normally the file size is between >> 5MB to 100MB depending on the physical size of the photo and whether >> it's black & white or color. 600dpi enables me to zoom in and see >> details that you can't normally see in the physical photo. >> > That's almost the opposite of what I might recommend. But then, I'm >looking at future output capability. > > A pristine, high contrast, document -- B&W @ 600 (720)... Most >modern printers have a native resolution of 600 (720 for Epson), and >since B&W only requires paper and pure black dots, a scan at that >resolution is effectively a "photocopy". > > Photos, if intended to be printed at "same size" get scanned at 300. >300PPI is considered optimal for high-end photoprinting (it's the >resolution used by NatGeo grade magazines). The convention is to have >the "source data" PPI at 2x the (halftone) LPI. On an old (non-photo) >CMYK printer, it requires a 16x16 dot "cell" to emulate full color >halftone. 150LPI (high grade photo halftone) means a printer putting out >2400DPI. Of course, modern photo printers with CcMmYK, or more, or with >variable size dots, can produce the color variations in less than a >16x16 cell. > > So... photos scan at 300*scale (where scale is the intended output >magnification: say a 4x6" photo to be printed at 8x12" => 2x -- scan at >600, reset resolution [Photoshop, say] to 300PPI. An 8x10" to be printed >at 4x5", scan at 150DPI, reset resolution to 300PPI). > > This applies to grey scale too, as producing full 256 levels of grey >(from white to black) also requires the 16x16 matrix (unless you have a >printer with half-black ink). Long, rambling response ;-) Some of the oldest photos don't even have 200dpi resolution. Hand-coated glass plate negatives did not have consistent resolution across the image. On the brighter side, there's little quality lost in making a contact print - assuming the negative plate is emulsion side down... The photos of my wife's grandparents' 65th wedding anniversary were taken with a 120 film camera (for the larger negatives) and 100 speed film (for finer grain) and a big flash unit (to use a small aperture for better depth of field). The 8x10 prints are very good and the inscription on the cake in the corner of the pictures can be read easily. Unfortunately, the majority of the family pictures I've acquired were made with inexpensive snapshot cameras (think plastic lenses) and "cheapest available" or "most convenient" processing - usually "when the roll is finished", so pictures with a processor-imprinted date of May include a snowball fight in Georgia. These prints are notable for their lack of resolution - and the number that are under/over exposed and/or out of focus and/or show camera/subject movement. If the negatives were available, I might be able to do more with the improperly exposed images (I have a negative scanner). In the current project of nearly 2000 pictures, there may be 30 negatives. Unfortunately, the outlook seems to have been "If you have the pictures, why do you need the negatives?" And the few remaining negatives are, at best, only marginally useful because they were loose in a drawer somewhere and have been nicked and scratched repeatedly. I plan to scan the negatives of pictures I have taken, probably at 1800dpi (higher would be better, but we're talking about thousands of 35mm negatives), with a thumbnail positive image for the image database (haven't decided on which one yet). The B&W negatives are sleeved and in 3 ring binders with at least some information about date/place/event. The color negatives are mostly in sleeves and stored with the prints still waiting to be put in albums. Most of these have date/place/event info with them. And then there are the digital-only images. The early digital cameras produced 300KB images on a par with tintypes (except that they're color). Will anyone have historically important pictures taken wih a cell phone? The current crop of 6MegaPixel and up cameras are capable of better images than most of the snapshot cameras of the 20th century - but how will those images be archived? Think how excited some genealogist will be in 2095 to find a memory card that's marked "Weathers Family Reunion - 2007" - and the letdown when there is no way of retrieving the data... I've tried to maintain backward compatibility as I've upgraded computers (usually by building my own). The latest machine (with dual format, double layer DVD writer) will also have a CD writer (not all DVD writers can produce a universally readable CD) plus 3.5 and 5 1/4 drives. John