BetterPhoto Q&A
Category: Problems with Images

RESOLUTION - WORKING FROM IMAGES SENT ONLINE

The question I have is, if a photograph is sent via the internet, isnt it automatically formatted as 72 dpi, and when I save it on my computer doesnt it stay at 72dpi? Is there software I can buy to allow customers to send it at a higher resolution? I want a resolution starting out with 600 dpi minumum for 5 x 7 or 8 x 10 prints. Please help, I am at a loss. fotonut73@aol.com

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February 06, 2004

1) Different people, different scanners.

The print's quality will be limited by the quality of the scan. If the customer's scan had a problem, then you will probably encounter problems when working with the image. YMMV.

Granted, people can take the image to a friend or a local place to scan, but then again, they might also be able to get it worked on there as well. :

2) Image resolution

By default, an image in JPG/TIFF/BMP format doesn't have a dpi. It is just data. 72dpi is the Windows screen resolution. Mac users have a 96dpi resolution.

When people scan an image with the software their software gave them, the file will be saved in one of several formats: jpg, tiff, bmp, pcx.

None of those formats really has a resolution to them. JPGs might have exif information stating a resolution, but it is up to the program reading the file to decide to use it or not.

The question of dpi is what output format will the final print take? If you want as much resolution now, 600dpi is fine for prints since they really don't have much resolution to begin with.

The problems arise when you ask people to send you the files in question to you over the internet.

Ie, speed of transfer.

Example:

Someone has an old 5x7 picture they would like you to restore. They scan it at 600dpi. This results in the following:

5 * 600 => 3000 pixels
7 * 600 => 4200 pixels

total pixels: 12.6 million.

Each pixel is comprised of 3 bytes on a 24bit scanner. 6 bytes if one a 48bit scanner.

So the size of the resulting 5x7 @ 600dpi scan will be about 36MB with a 24bit scanner.

You can expect that one image to take the following amounts of time depending on their connection to the internet:

dial-up modem:
14.4kbps => 5 hours, 44 minutes
28.8kbps => 2 hours, 52 minutes
56kbps => 86 minutes

isdn line:
144kbps => 33 minutes

dsl/cablemodem upstream:
128kbps => 38 minutes
256kbps => 19 minutes
384kbps => 13 minutes

If your customer has a good high speed connection, no problem. If they are still in the world of dial-up because they can't get access to high speed, then it might be a problem. In which case, physical media would be good: CDR, CDRW, DVDR/RW, and/or zip disks.

There are tools which allows people to send high resolution images in a much smaller file size, but those tools are not free: Genuine Fractals from lizardtech.

The other problem is that of JPEG or lossy compression. If someone sends you a file which was compressed alot with JPEG compression, you would lose a good deal of image information.

One other possibility is to have negatives or slides made of the pictures and have them send those to you by mail. That way, you have something solid to work with and can scan to whichever resolution you want.

But that incurs cost on the customer. :

Short answer:

- Having people scan for you and sending you the images on CD is fine. Just bear in mind to detail out explicit instructions on how to scan and what format to use. Do not assume that the customer has a particular type of software, but inquire so that you will know how to best work with that customer.

- Sending files over the internet is fine... for smaller files. When the files become huge, you have problems of reliable uploads. 72dpi is your screen resolution, not the picture resolution. You set that when you work with the image.

Good luck!

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February 10, 2004