Re: Digital Photography of Text on 8 1/2" x 11" Paper
- From: Alan Browne <alan.browne@xxxxxxxxxxxxxxxxxxxxx>
- Date: Sat, 01 Nov 2008 12:47:11 -0400
I'm using a digital camera on its "macro" setting (for close-ups) to
take photos of text on letter-size paper. The focus distance is 15 cm
- 20 cm (6 in - 8 in). To get the entire letter-size page into the
viewfinder, the camera is about 33 cm (13 in) from the page.
To compensate for the out-of-focus distance, I've set the camera on
maximum resolution (2592x1944) and highest quality (Super). But then
the maximum number of photo's I can take is seriously reduced.
Don't really have the time to shoot, upload and compare images with
all the different possible combinations to see whats the best tradeoff
between readability and memory usage.
I know very little about photography or digital photography and the
User's Manual is woefully inadequate in explaining even the camera
functions. It is no help at all in giving photography tips.
Is someone here familiar with text photography and able to explain
what effect reducing the resolution and quality will have on the
readability of text photography?
Vivitar ViviCam 5299
2.4" Color TFT-LCD
Zoom: 4x Digital
Lens: Focus Free f=8.25mm, F=3.0
Focus Range: 15 cm - 20 cm, (Macro0, 1.5m ~ infinity (Normal)
Image Resolution: 2592x1944, 2048x1536, 1600x1200, 1280x960, 640x480
Video Quality: VGA 640x480, QVGA 320x240 at 30 or 15 fps
File Format: JPEG, EXIF 2.2, DCF 1.1, MJPEG (AVI)
Not exactly the right rig for copy work. What really drives the "input" is your desired output. I assume you want to print these pages at some point, so a desirable dpi is 300 (though 150 would probably suffice if the print is not too fine).
Where these cameras say "macro" it really means "close up". True macro means the image on the sensor is the size of the subject (or thereabouts). That does not matter here, really. You want the page to fill the image as much as possible. That is your main goal.
Think of the output print the same size as the paper you're scanning.
So 8.5 x 11 would require, say, 300 dpi output. Here that means 300 dpi input from the sheet. So a desired resolution would be:
8.5 x 300 = 2550 X
11 x 300 = 3300 = 8.4 Mpix desired resolution in the camera.
But, if the print is not too fine, then maybe you can reduce that:
8.5 x 200 = 1700 X
11 x 200 = 2200 = 3.7 Mpix desired resolution in the camera.
(Your 2048x1536 should do well for about 186 dpi or better if you 'crop in' while shooting (don't photograph the blank margin space)).
Other: Light the paper well from two sides with approx 45 deg. angle to the paper. Look for even lighting in your first images (no glare or wild contrast differences. Matt paper=easy; glossy=more care needed).
Do not use the built in strobe. The lighting at the paper will be uneven and if the paper is fine enough or glossy, you'll get a strong blob.
See if you can stop down the aperture of the camera a little ... to about f/8 (and light the paper brightly). (Will increase the sharpness and contrast).
Exp. compensation: because the camera wants that white paper to be grey, it will underexpose a little. Set the exp compensation to about +1.5.
In essence, for this kind of copy work contrast is all important. That means the appropriate dpi sampled, good lighting (strobe is better if you can do that, but must be from the sides), and a slightly stopped down aperture.
Try to shoot at ISO 100 - 200.
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