Home   Back to Tutorials


Processing Digital Images

By T. Zinneman

More and more people are producing digital images, either by using a digital camera or by scanning existing photographs.  They are then faced with the problem of what do after getting them on their computer’s hard drive.  I would like to review seven basic steps that should be followed after uploading digital images to your computer.

One needs an image editing program to perform most of these steps.  There are many such programs available ranging in cost from a few dollars to several hundreds of dollars.  The program Irfanview, available as a free download (see www.irfanview.com), is an excellent image viewing program that also contains enough editing functions to perform the tasks described in the following steps.  Other good programs include Adobe’s Photoshop and Photoshop Elements, Corel’s PhotoPaint, Roxio’s PhotoSuite, Microsoft’s PictureIt, Jasc’s PaintShop Pro, and Ulead’s PhotoImpact

Step 1 – Preserve all original images.

The first and most important step is to make a backup copy of all your digital images before doing any editing or processing.  This can be done by using a CD/DVD burner to copy your image files to a CD or DVD.  The backup disk should then be stored in a safe place and used only when something happens to the image files on your hard drive.

Step 2 – Select best images and delete the rest.

After backing up your image files, you are ready to review the files on your hard drive.  This can be accomplished quickly using a program that has slide show capability.  If you take a lot of pictures, you’ll find some that are not properly exposed, properly focused, properly framed, or duplicates.  Keep the good images and delete the rest.  You may find yourself deleting anywhere from 30 to 60 percent of your images.  This saves disk space and cuts down on clutter.  Remember, you still have the backup created in Step 1 that contains all of your original images, so you can still retrieve images that you deleted if necessary. 

Step 3 – Crop and resize selected images.

After examining a selected image, you may find that it may be better to eliminate part of the scene.  This can be done by using the cropping tool.  Use this tool to draw an adjustable rectangular box around the part of the image you want to keep and then select the Crop command.  Anything inside the box is kept; everything outside the box is discarded.

After cropping your image, you may want to resize it, that is, change the number of pixels in the image.  This is especially important if you want to attach the image to an e-mail message and transmit it over the Internet.  If so, you should resample your image to 640 x 480 pixels or less using the Resize/Resample command.  By reducing the number of pixels, you reduce the file size, which reduces the amount of time to upload or download your images from the Net.  Since the average computer monitor is set for 800 x 600 pixels, this also means that the complete image will appear on the screen.  If you want to print the image, you should not resample your image; keep the maximum numbers of pixels.  A good print requires approximately 200dpi.  Thus, a 4 x 6 print requires 800 x 1200 pixels.

Step 4 – Adjust contrast and brightness.

The most common problems associated with digital images are brightness and contrast.  More often than not, the images are darker than desired.  Adjusting brightness can be used to darken the highlights or lighten the shadows of an image.  Adjusting contrast changes the difference between the light and dark areas of an image.  Low-end programs typically provide a dialog box with slider controls for adjusting the brightness and contrast.  Mid-level and high-level programs provide a tool, called a histogram, which provides a much more effective method to adjust brightness and contrast.

Step 5 – Adjust color balance.

Occasionally, you may find it necessary to make some color corrections, such as removing an unwanted color cast, adjusting color saturation, or correcting a color mismatch.  All image editing programs provide several commands to fix these problems.  These commands range from simple slider controls for adjusting color balance or saturation and hue to more sophisticated methods, such as the histogram.

Step 6 – Sharpen your image.

The last adjustment to be made is to sharpen the image.  Practically all digital images at one time or another are exposed to interpolation.  Interpolation tends to soften an image.  Sharpening the image will restore the image’s clarity and enhance the edges.  All image editing programs provide sharpening commands.  These range from simple slider controls to the more precise Unsharp Mask command, which will be found under the Filters menu.  Again, applying the sharpening command should be done last, after all other image adjustments are made.

Step 7 – Save your image.

After editing is complete, you are ready to save your image.  Use the Save As command on the File dropdown menu.  When the dialog box appears, change the file name.  I usually add a w or p (for web or printer) to the file name before the extension.  By using the Save As command, you preserve the original file.  If you use the Save command, the original file is replaced by the edited file. 

If you’re saving the image as a .jpg file, which is usually the case, you have the option of adjusting the amount of compression used.  If the file is to be transmitted over the Internet, use a quality factor of 2 to 4 (based on 10 being the best).  If the image was re-sampled to 640 x 480 or less (Step 3), the resulting file size after compression should be approximately 30KB to 60KB, which is suitable for transmitting over the Internet.  For example, if using a telephone modem, this should result in a transmission time of 6 to 12 seconds.  If the image is to be printed, a high .jpg compression factor, around 8 or 9, should be used.  Of course, this will result in a larger file size, but enough detail is preserved to make a good print.

The above seven steps provide a simple and orderly procedure for processing your digital photos.  Of course, additional editing functions, such as adding text or borders, can also be used to enhance your photos.

 

T. Zinneman is a member of the Photo Adventures Camera Club.  If you have any questions or comments, please send them to tzinneman@comcast.net.