Optimizing picture file size

Three things you can do to lower file size  Lower the resolution  Crop the picture  Save with a file format that uses compression

What tools do you need? Microsoft Paint comes free with Windows. If you are using Windows 2000 or Windows XP, paint supports saving in compressed formats. These instructions use the features in Paint because it is available to most people. The techniques can be used with more advanced programs like PhotoShop or Paint Shop Pro with even better results.

Dropping the Resolution  What is Resolution?  How can High resolution be bad?  How do I drop it?  What do I lose?

What is Resolution? Pictures are made of pixels. A pixel is a single dot in the picture, and the computer stores a number that represents what color that dot is. The more little dots you use to represent the picture, the clearer the picture is. Good ResolutionLow ResolutionPoor Resolution

How can High resolution be bad? A common resolution for monitors or projectors is 1024x768. That means the display has dots in 1024 columns and 768 rows. A 5 Mega pixel camera takes pictures that are 2592x1944. The application that displays the picture must throw away 85% of the pixels - they will not fit. The file could have been 1/6 th of the size and display the same.

How do I drop resolution? To drop resolution with MS Paint  Click Image  Stretch/Skew  Pick a scale for Stretch. For example: if you enter 50 for and 50 for vertical, This will make your image half as wide and half as tall. In this example, You actually end up with 1/4 th as many pixels. Your file could go from 500K to 125K.  Click OK ½ ½ ¼ th of the original area

What do I lose? You lose image quality. If you drop the resolution too much, your picture will become less clear. It may take a couple attempts to find a good size where you have only dropped the wasted resolution and the inserted picture looks the same as the full-size picture. Good Resolution 8 KB Low Resolution 2KB Poor Resolution 1KB I did not include a “High Resolution” sample because it would display the same as the “Good Resolution” Sample.

Cropping  What is cropping?  How do I crop a picture  What do I lose?

What is Cropping? Cropping means selecting a portion of a picture and eliminating the portion outside the selection. Cropping is not just for file size conservation. You may want to use it to re- center a picture or eliminate unwanted portions of a picture.

How do I crop a picture? If MS Paint is all you have available…  Select the area you want to keep  Click Edit  Copy  Click File  New  Click Image  Attributes  Specify something small, like 32x32 and click OK  Click Edit  Paste. Click Yes when asked if you want the bitmap enlarged Other applications make cropping quicker and easier. If you have access to a full-featured photo editing package, I recommend using it.

What do I lose? In this case, the only thing you lose is the portion of the picture you cropped out. In most cases, when you employ this technique it is because the image shows extra, uninteresting scenery and you could still convey what you need with a portion of the picture.

File formats with compression  What is compression?  Which formats use compression?  How do I use a compressed file format?  Can I double Compress?  What do I lose?

What is compression? An uncompressed file contains a list of every single pixel and a code for the color of that pixel. Some file formats look for patterns in the picture and save a mathematical description of the pattern instead. This significantly reduces the file size, especially in pictures with large areas that are the same color. The main drawback is during compression, the application will typically use approximations when a section of a picture closely resembles a simple mathematical representation, but does not fit exactly.

Which formats use compression?  JPEG (.jpg) is the most popular compressed format. It uses a standard that efficiently reduces file size with very little reduction in quality. The format also supports allowing the user to select the level of compression so you can decide how much quality you want to give up in the name of smaller size.  GIF (.gif) is another popular compressed format. GIF achieves it’s compression levels by limiting you to 256 colors and using compression techniques similar to WinZip, where the actual data stays the same. This makes GIF a good choice when text is used in an image, because it will not use approximations which can make edges of letters fuzzy. GIF will often surpass JPEG in file size reduction for images with less that 8 colors. With photos, GIF will often lose too much quality to be useful.  TIFF (.tif) is another popular format which employs some JPEG type techniques while remaining text friendly like a GIF. The reduction in file size is not as efficient as with a JPG.

How do I use a Compressed Format?  When you save your file after making changes, make sure “Save As Type” has a compressed format (such as.jpg) selected.  MS Paint has very efficient compression. Although the save options to not give you a choice for the level of compression, it is often worth opening a file before you send it and saving it with a different name from Paint to see if you get a smaller file.

Can I double Compress? Double compressing can be achieved by taking a compressed file format like GIF or JPEG and using a utility like WinZip to compress it further. This rarely makes the file smaller since the compressed file format usually employs enough compression that WinZip cannot find ways to further recude the size. Often it actually makes the file bigger since WinZip must add some information so the recipient’s computer knows how to decompress it. With very large files, it still may be worth a try.

What do I lose?  GIF compression always drops your image to 256 colors. In most pictures, this replaces large areas of detail of similar colors with one color. GIF is best avoided for photos.  With JPEG type encryption, you lose quality when the compression finds places where it can approximate patterns that nearly match the desired image appearance. Good Level of JPEG compression - 8 KB Same image with too much JPEG compression - 3 KB NOTE: An uncompressed Bitmap this size would be 104 KB!

If I follow all these tips, how much file space does that save? The original version of the picture below was 1,409 KB. The size of the picture as it appears is 23 KB.  With a 56K dial-up connection, the original would take 4 minutes to download. The smaller one would take 4 seconds.  If you were to use a $12/MB satellite connection, the large file would cost $16.52 to transmit, the small version would cost 27 cents. (Don’t forget to double the costs if a single recipient also uses satellite)  A floppy disk could only hold one image of the original size. It could hold 64 images like the smaller version.

Is there any time I should not reduce file size?  If your picture will be printed in a proposal, brochure, formal report, or released to the press, keep the original high resolution quality.  Always keep a copy of the original with the original quality. Work with and transmit small files, but you may later want to revert to the original quality image.  If you are printing on photo quality paper, the original quality will give you a better looking picture.  If your picture will be enlarged on a plotter or large format printer, the trade-offs of size optimizations will be magnified and probably unacceptable.