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173 - Cropping and Enlarging Pictures By Scanning

In last week's bulletin, we discussed the use of appropriate resolution when using digital cameras or scanners. You learned that too high a resolution, while capturing more detail, is still just a waste of time and storage space if the image is destined to be shown on your computer screen. In this week's bulletin, you will consider a different aspect of resolution. When scanning old photos, the images are often small or damaged. Wouldn't it be nice if you could enlarge only the best part of a photo to be big enough to fill your computer screen? You can, and this tip will tell you how. It is a bit long this week. If you are not going to be involved in scanning, you might want to just remember it's available on my website at a later time, when you might need it.

Let's review the topic of Screen Resolution first -
Computer screen resolution is usually set to one of two common settings, either 800x600 or 1024x768. You can check your setting by RIGHT-clicking on the desktop, selecting Properties, then selecting the "Settings" tab. In the lower left portion of the window, you will see the current setting for your monitor. For our example all through this bulletin, I will use the setting of 800x600. That means the screen will be set to display 800 pixels across and 600 pixels high. If you try to display a picture that is 1000x700 pixels on this screen, there will be 200 pixels of width and 100 pixels of height which will fall out of the viewing area at any one time. The extra pixels will simply fall off the edges of the screen and not be seen. You will have to slide the vertical and horizontal scroll bars to see remainder of the picture. You have probably observed this problem in photos sent to you by friends.

What does that mean to you?
The reason you will care about this when scanning photos is that you will want to scan your photo so that it is large enough to fill the screen, but not so large as to exceed the size of the screen. Using our example of a screen set at 800x600, if you scan a 3" high photo at 400 dpi (dots per inch), the resulting height of the scanned image will be 1200 dots (pixels) or twice the height of your computer screen. In all cases, a little planning before scanning produces a much more useful picture for your computer screen. Follow these suggestions and any of your scanned photos can be sued as your wallpaper (the background picture on your desktop).

A word about newer versions of Internet Explorer -
The industry has recognized how frustrated people have become when trying to view photos too large for their screens. Newer versions of Internet Explorer, and other viewing programs, come with a built in feature which shrinks a too-large image just enough to be viewed in the available screen area. Internet Explorer allows you to click on an icon to expand the photo to it's full size. Click on the icon again and it shrinks back to fit in the available space.

While this is all well and good, it is only a partial solution to the problem. If you scan at too high a resolution, you will take up much more disk space, take longer to display the picture, and make it as much as 100 times longer to download to your firends! Worse yet, as we discussed last week, the picture seen on the computer screen will be no better than if you had used the proper scan setting to begin with.

Recommendation #1 - Scan for the most universal result.
I suggest that you scan with the 800x600 resolution in mind. Here's why. It will result in the most universally acceptable result. At 800x600, the picture will fill a screen of that size. If it is later displayed on a computer set to 1024x768, the photo will still be large enough to fill most of the screen and it will look just fine. You can try some experiments to see what I mean. If the recipient happens to use a resolution even higher than 1024x768, they are already accustomed to viewing everything much smaller than you and I prefer. They will not be surprised to see the smaller photo.

But what if my photo isn't the same "shape" as my computer screen?
Start with this thought - Your photo ISN'T the right shape! Photos come in all shapes and sizes and none of them are right. This is where the real dilemma starts! What do I mean by shape? I mean the ratio of the width to the height. A computer screen is 1.33 times wider than it is tall. A 6"x4" photo is 1.5 times wider than it is tall. Other photo sizes are even more out of proportion, relative to a computer screen. Scanners only scan at one setting as they pass over the object. Tell the scanner to scan at 150 dots per inch and both the width and height are scanned at that resolution. From there, it's just simple math. The 4" height of the picture will produce 600 pixels in height (150dpi x 4" = 600). The 6" width will produce 900 pixels in width (150dpi x 6" = 900). Whoops! The screen is only 800 wide. What now?

A judgment call has to be made.
Choice #1 is to decide to retain the full content of the original photo. By scanning at 133 dots per inch, we retain the full width of the photo while having in the photo not fill the screen height fully. (133dpi x 6" = 798) is full width. (133dpi x 4" = 532) is less than the screen height of 600. Still, none of the photo was lost, and that was our reason for choosing this option.

Choice #2 is to "crop" the photo. Cropping is where you draw a box around the part of the photo you want to scan, telling it to ignore the rest. Cropping allows us to establish the desired proportions of width to height. In effect, we are cutting off the extra 100 pixels from the width ahead of time so no scrolling will be needed to view the final result. We can crop both the left and right edges at the same time, so the subject is also centered in our photo - an added benefit.

How do we crop "sideways" pictures?
Admittedly, that last one was a simple example. Now, let's consider more complex examples. What if the photographer turned the camera sideways when he took the picture? Some people like doing that. The picture is printed sideways, but we will scan it turned so the subject's head is facing up. Now, our 6"x4" photo is really 4"x6". Again, we have the same two choices but now we can start being creative in how we scan.

Choice #1 is to scan the photo at 100 dots per inch, producing an image that will be as tall as the screen, but only half the width of the computer screen (100dpi x 4" = 400).

Choice #2 is to crop the photo, and this is where it gets interesting. Let's say this sideways picture was of your best friend. As you go to crop it, you realize that the original picture has a lot of open sky above her and a lot of sidewalk below her. Why not crop that from the picture? That will make her appear larger on the screen and you don't care about the backdrop anyway. In fact if you cut off her feet and lower legs, the remaining picture is very close to being in the correct proportion for the computer screen. There you go! You've just crossed over into the creative part of this process! You just edited a bad photo, taken too far away from the subject, into a really nice photo of your best friend!

How do I enlarge pictures?
What I haven't focused on just yet is that when you crop, as in our last example, the area to be scanned is getting smaller. This allows you to scan at a higher resolution than before. The idea is to use a smaller portion of the original photo but scn it at a higher resolution, producing the same size final image but with an enlarged subject! Just do the math. If you were scanning a photo earlier at 150dpi, but you cropped it from 4" high to 2" high, you could then scan it at 300dpi to get the same height on the computer screen. (150dpi x 4" = 600) (300dpi x 2" = 600) Scanner software always displays the image size in some form. With your handy calculator, you can figure out the scan setting you need to fill the screen height or width! You've enlarged the subject!

Can we make it easy to decide on the scanning resolution?
We can try. If you're not cropping, I've created a cheat-sheet table for scanning photos of the most common sizes. The "dpi" settings will produce images that fill an 800x600 screen. Look at the table below and notice that if you are scanning a 4"x6" photo, the dpi for height and width are different. This is where you choose how you want to scan. If you choose to base your scan on seeing the full height of the photo, you scan at 150dpi. If you choose to base your scan on seeing the full width of the photo, you scan at 133dpi. Here's the process in steps:

  1. Measure the width and height of the photo your are about to scan.
  2. Decide whether to base your scan on the width or the height of the picture.
  3. Find the photo size on the table row (4"x6" is the third row down in the table).
  4. Set the scan to favor the height or the width (or in between as a compromise).
Scanning Resolution Guide for Common Photo Sizes
Height Height Based Width Width Based
3.5" 171dpi 4.5" 178dpi
3.5" 171dpi 5.0" 160dpi
4.0" 150dpi 6.0" 133dpi
6.0" 120dpi 8.0" 114dpi
8.0" 75dpi 10.0" 80dpi

And one closing note: The table above is a small subset of a spreadsheet I have developed for working with scans ranging from photos of 1.5"x1.5", up to 7"x7", in tenths of an inch. If you really get into scanning large numbers of different shaped photos, this spreadsheet would be very helpful. Send me an email requesting the full spreadsheet and I will be happy to forward it to you.

This bulletin was a bit long but it's really a primer on how you go about scanning. I tried to keep it straight forward and to segregate the main points of interest. It would have saved me many hours to have had some guidance when I began scanning. I hope this will help you get started more easily when you do.

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