Thanks to all for replying to my question. Here is some additional info on
this. This scan was for a genealogy magazine.
First, go to the following web site:
http://www.familychronicle.com/photosubmissions.html
The February 2004 issue of this magazine extended the time to forward photos
by e-mail or the USPS.
I was scanning an old black and white photo (1901 saloon interior) which was
9-3/4 inches x 7-3/4 inches. I scanned the photo at 300dpi in color. I
compressed the file into jpg format. The instructions in the web site above
said to use medium compression and to keep the file size under 1 meg. When I
did so, much of the detail was lost. The software was Visioneer PaperPort,
version 6.1
The other option for submitting photos was to have a color photocopy made and
forward same via the U. S. mail. This is what I did.
George Nuetzel
I agree with tomcas that if it was a B&W photo, Grayscale would be good.
Color mode is OK, but the image size is 3 times more bytes than necessary for
a B&W photo.
This size data gives an image size of:
(9.75 inches x 300 dpi) x (7.75 inches x 300 dpi) = 2925 x 2325 pixels
For RGB color, there is 3 bytes per pixel, 2925x2325 x3 = 20.4 million bytes
For grayscale, there is 1 byte per pixel, 2925x2325 = 6.8 million bytes.
This is the uncompressed size in memory. Grayscale is 1/3 the size.
The byte size above only depends on the size in pixels, nothing else.
Higher resolution will create more pixels, lower will give fewer.
The photo size in inches is directly proportional to output size.
Then JPG compression will reduce the file size. There are no absolutes,
because compression does vary with the photo content, large featureless areas
(walls, skies) compress much better than highly detailed busy areas. Two
extremes of same-size images with different content in this way might have a
2:1 file size ratio from each other, all else equal. And color compresses
better than grayscale.
Moderate compression is maybe a JPG Quality factor of 8 (or 80), but this
setting also varies with different programs, again it has no exact or
absolute meaning or value. They ask for JPG, but you probably want at least
8 for reproduction, maybe more. Moderate probably means a decent compromise
between a small file and good image quality, that is, very few detectable JPG
artifacts. A higher JPG Quality factor is a larger file but better image,
lower is a smaller file but worse image quality due to JPG artifacts. You can
adjust file size with JPG Quality, but image quality also varies.
I see they say a color copier is acceptable, so it doesnt sound like the
highest quality standards necessarily apply.
This image in color might be JPG compresed from the 20 million bytes to maybe
1.2MB file size (a range around that). In grayscale, from 6.8 million to
maybe 900KB file size. These numbers are anything but sacred, but is merely
one possiblity (a guess I made). Less JPG compression (higher Quality
number) than this will be a better image (larger file). Again the file size
depends on the image content and the JPG Quality setting (and image size in
pixels of course).
File size really depends on every parameter. If you started with a 4x5 inch
photo, the 300 dpi file would be smaller. If you had used 200 dpi, it would
be smaller. Color/grayscale affects it, and JPG Quality too. And image
content and phase of the moon. <g> But there are big broad ball parks.
The magazine specifications seem incomplete, because they dont mention the
size it will be printed, which is all important. I suspect they will not
print this large image at full 9.75x7.75 inch size. That full size would be
near full page size for many magazines. Is this a full page type of photo?
For one example, typical school yearbook photo size (many per page) is
printed more like wallet size or smaller. I suspect their instructions
assume you will start with a smaller photo, wallet size up to snapshot size?
Your photo is basically 8x10 inches, surely larger than most, which is why
your file was larger than most.
If they instead printed this large image in the magazine at say 1/4 page
size, then the printed dimensions (inches) might be half of your original.
Half dimensions means that you could scan this large image at 150 dpi, and
then scale it to half size at 300 dpi. This half size (or 150 dpi) reduces
the uncompressed size to 1/4 of the byte numbers above.
Or if you had started with a 4x5 inch photo, you could have made the 1MB file
size easily.
Anyway, it would have been better if they specified the size it will be
printed in the magazine, like maybe they were going to print it as 3x4
inches, at the 300 dpi. Numbers like this are probably their real goal,
regardless of your photo size, and then you would know the goal too. Seems
important. For example a too-small photo might need to be enlarged, or a
too-large photo reduced. I suspect they had some assumption about that
printed size and photo size, but they didnt seem to say. It probably could be
because they thought it might be hard to explain all the basics of printing
images to everyone, so they simply say 300 dpi and assume they can work from
whatever they get.
You dont need 7 or 20 megabytes for that smaller printing 1/4 page size.
However I am sure they can deal with a larger image, it shouldnt be a
problem. Too small can be a problem.
Hope this helps.
