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Scanning and Saving Images
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This magazine is edited for anyone interested in photography and offers illustrated, incisive instructional articles. Its departments cover all facets of photography from color film use and development to large format equipment. In addition, it contains information about collecting photographic equipment and news from the international photography world. It also answers readers' questions and offers buying advice.
On these pages I hope to give you a little insight into image resolution. From scanning to digital cameras to printing to JPG files for the web. The first example is a comparison of scanning at different resolutions. With the new scanners on the market at under $100 offering optical resolutions of 1200 x 600 ppi resolution, what resolution do you need for publishing your images on the web. 72ppi  The 72 dpi number is vaguely about the SIZE we see, but we do see different sizes. The screen settings most of us choose are generally in the 72 to 100 dpi ballpark size, more or less.  Thats right, 72 pixels per inch is all a computer monitor can display. What I believed was scanning at 72 ppi saved time and created a better image than scanning at a higher resolution and re-sizing it in my imaging software.

What I found was , to some degree, surprising. The difference in scan time at 72 ppi and 300 ppi did not exist. The reason for this is that the scanner always scans at its optical resolution so that at 72ppi its still scanning at 300 ppi and throwing away the extra data.

The difference in the images was indistinguisable until you enlarged the images. So take a look at the following page and see for yourself. The third small image is the same image as the large image on the page. If you right click on the three small images and select "properties" you can see the image sizes. You'll notice the primary difference is in image size and not in what you can see on screen.

The primary advantage to scanning at 300ppi is that if you plan to print your images in color on an inkjet printer all you have to do is scan once and resize in your image editor for your web images. If you plan on printing your images be certain to see the section on "The effect of scan resolution on printing".

Page 1- scan resolution comparison

The second page gives you an idea on how compression ratios in the JPG format affect your image size (thus load time) as well as the overall image resolution (detail). JPG is a lossy format.  What that means is once you save an image in the jpg format, the information that was discarded to save image size can not (CAN NOT) be recovered. For this reason, any time you scan a photo, or capture a digital image from a camera, save that image first in a non-lossy format ( i.e. BMP or TIF) and do all your editing to that base image. Do not (DO NOT) save over that image or the changes will be permanent.

So take a look a the next page and see how changing the compression ratio when saving in a JPG format affects image quality and load time. What you will find is that to get you pages to load in a timely manner you will have to limit the number of images on a page and sacrifice some image quality (it does not have to be perceptible to the nake eye) to keep your overall page size down. And for folks with graphics rich pages(you know who you are) or people with music ( large files) this all adds to load time. So clear out all the extraneous junk (cutesy animations, etc) and stick with the stuff you really want people to see. Excessive load times drive away surfers faster than anything else.

Page 2 - Compression ratio comparison



In this section we will take a look at the effect of scan resolution on printing.
Page 3 - Effect of scan resolution on printing


    

So you're already to get your images ready for the web. The two common formats are JPG and GIF. Which one is right for your images? Look at these quick comparisons and you'll know immediately which ones to use.
Page 4 - What file format should I use?




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