With computer monitors, scan resolution merely determines the size of the scanned image (height and width) on the computer screen. Many people think a greater scan resolution shows more detail in a photo.
This is generally true somewhat, but it’s only because it makes the image larger. However, higher scan resolutions make the image files extremely hefty and our computer screens are simply not large enough to view these higher resolution images at 100 percent scale without scrolling horizontally and vertically without scaling.
When we increase the scan resolution, it increases the image size. A little goes a long way, and there is no advantage in working with extremely huge image files just to discard most of the pixels when we display them online. Simply stated, do not scan at a high resolution when there is no need for it. Scanning at a higher resolution for archival or printing purposes is a different matter however.
By scanning at a smaller resolution, you will have manageable file sizes, which will create a quicker download time when your photo is viewed online. The online recipients of your photographs will certainly appreciate the smaller file size.
To determine the size of the photo on your computer screen before scanning, you simply multiply the original photo width by the scan resolution to be selected and the original photo height by the scan resolution to be selected. For example, a 3x5 photo scanned at 100 dpi will result in a photo that fills a 300 x 500 pixel area (3 inches x 100 dpi) x (5 inches x 100 dpi).
In order to illustrate how scan resolution works, you can perform this simple experiment. Scan a photo at 100 dpi resolution and save it as a TIFF file naming it Image100dpi. Now scan the identical photo at 300-dpi resolution and save it as a TIFF file naming it Image300dpi.
View both images at 100 percent. By comparing the two scans in your preferred graphics program you can see that Image300dpi is 300 percent larger than Image100dpi on the screen.
We should remember to not carry image resolution in scanning too far for simple online presentation. By keeping your scan resolution smaller - say 100 dpi for online presentation, the end result will be image files that are not overly large in both screen size and file size, but the photo quality shows very little difference, if any at all from that of a higher dpi on your monitor screen.
Now, on to graphics files. There are many different graphics file types. When saving a scanned photograph, it is important to save the file in a “lossless” format. Some formats are “lossy” - that is, when saving a file, it will remove photographic data in the file, as it compresses.
Three graphics file types have become among the most universal formats over the years. The TIFF (Tagged Image File Format) file format is a “lossless” format and retains all of the image data. The TIFF format is also an excellent format for printing.
TIFF makes an exceptional file format for an archival photograph to be stored on your computer or storage media. TIFF file formats have become a standard for the large computer-based publishing industry.
Many people display their photographs on web pages, or send them to family and friends via e-mail. For electronic presentation and distribution such as this, an excellent file choice is the JPEG file format.
The JPEG (Joint Photographics Expert Group) format is very well suited for presenting detailed photographic images on a computer screen, while the GIF (Graphic Interchange Format, pronounced “Jiff” and also “Giff”) file format is more suited for the presentation of simple color illustrations and clipart.
GIF files are limited to only 256 colors and this is why they are unsuitable for many color photographs, resulting in both poor image quality and large files. However, JPEG (pronounced “Jay Peg”) is a “lossy” file format, in that each time you open, edit and save the file, you will loose some photographic quality.
So it is better to save your original scan as a TIFF file and work from that file, After all changes are made to the open copy of a TIFF file, you then export the FINAL result as a JPEG file and retain the original TIFF image for archival editing purposes. By doing this you will preserve much of the photograph’s quality in the final JPEG file.
Graphics programs allow you to set the compression of the photograph when saving as a JPEG. A higher compression rate gives less quality, but produces a smaller file size resulting in faster download times. Personally, I try and keep all online photos below a 60k file size and I always try to keep the compression rate less than 20 when saving as a JPEG.
There are many excellent resources available related to scanning – from books to web sites. One of my favorite books in my personal library on the subject is Make Your Scanner a Great Design and Production Tool by Michael J. Sullivan. And the genealogist can find many free online resources for scanning. Below are just a few of the scanning resources available online:
A Few Scanning Tips
Getting Started Scanning
Tips on Scanning