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Front Page » July 10, 2007 » Tech Tips » Digital Imaging
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Digital Imaging

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Sun Advocate/Progress Network Administrator

Graphic File Formats

Smoke from the prescribed Jungle fire north west of Ferron drifts down the canyon towards town, past South Horn Mountain like a silky blanket. In addition to the prescribed burn, several wildfires in the central part of the state have helped contribute to the smoke that has hovered over the communities of Carbon and Emery counties over the past few weeks.

With scanners and digital cameras more popular than ever, consumers may wonder what format is best suited to handle the task. This question is often raised when a photo has been scanned and the computer user is ready to save it onto their computer. What type (format) should they use?

In reality, there isn't a "best" format per-se. Each format has its benefits and its drawbacks.

There are literally dozens of graphic formats, but all of them fall into two basic categories (or a combination of the two) - raster and vector. Raster graphics, like digital photos & scanned images, are composed entirely of colored "dots" (i.e. pixels), where vector graphics, like clip art and oftentimes logos, are instead composed of mathematical computations.

The main benefit of vector graphics is that because they aren't composed of pixels they can be scaled to any size, large or small, and will still print with the highest quality. Raster graphics, on the other hand, have a limited number of pixels, and therefore have a limited quality and print size.

By far, the vast majority of consumers work strictly with raster formats. And of those formats, the most popular formats are TIFF and JPEG. This is because both formats are well supported on virtually all computer platforms, from Windows to Linux and Mac OS-X.

Both formats can employ compression to make the graphic file smaller. Meaning, to make the graphic file take up less storage space on the computer. But each format uses compression in a different way.

Of course compression doesn't affect an image's visual dimensions, but rather how much information will need to be stored on the computer to describe the image. Typically this is measured in units like kilobytes (KB) or megabytes (MB).

The TIFF format can employ several types of compression, but by far the most common is LZW. LZW is a lossless compression method. The term "lossless" means that the compression makes the graphic's file size smaller without damaging or degrading the visual quality of the graphic.

LZW is also fully automatic and doesn't require any input from the computer user. Most graphic editors simply require the user to invoke "LZW" option, like a check box or radio button, when the image is first saved.

JPEG, in contrast, uses a "lossy" compression. That means the compression makes the file size smaller at the detriment of the graphic's visual quality. JPEG compression is variable (and entirely controllable by the computer user), where the more compression used not only makes the graphic's file size smaller, but at the same time makes the quality of the graphic lessen.

So, on one end of the spectrum, low JPEG compression creates bigger files with higher image quality, and on the other end of the spectrum, high JPEG compression creates smaller files with very low image quality.

A plume of smoke drifts upward from the prescribed Jungle fire north west of Ferron, coloring the horizon. With exceedingly hot temperatures and dry conditions throughout the area, Carbon and Emery recreationalists should be extra cautious while in the outdoors to help prevent additional wildfires.

Many image editors use a number scale for JPEG compression. When a user saves a graphic as a JPEG, they are asked to specify the "quality number" before the program can continue. Photoshop uses 1-12, where 1 is low quality (high compression) and 12 is high quality (low compression). Corel's Paint Shop Pro uses a larger scale, from 1-100, where 1 is low quality (high compression) and 100 is high quality (low compression).

Regardless of the graphic format, excessive "lossy" compression will have a negative impact on the image quality and can cause blur, distortion and major "pixelation" which may make the image look choppy.

For the best possible quality, TIFF is the best option. However, TIFF files tend to be much larger in file size than JPEG. A TIFF image with LZW compression can be 3 or 4 times larger than the same graphic saved as a JPEG with low compression. As a result, sometimes the TIFF format isn't always the most practical option.

This is the very same reason that virtually all digital cameras save photos as JPEG images. Imagine only being able to take perhaps 40 or 50 digital photos (as TIFF images) on a single camera card instead of maybe 200 photos (as JPEG images). Or picture fitting 100 photos on a CD instead of 300 or 400. Most camera manufacturers will agree that JPEG with low compression provides a good balance between file size and image quality - at least for most consumers.

One important note regarding the quality of image formats is that they preserve quality, not improve it. Saving a JPEG graphic that is already highly compressed with noticeable visual degradation as a TIFF graphic won't improve the quality of the image. However, saving a high quality TIFF image as a low quality (high compression) JPEG will have a dramatic impact on the quality of the image.

One question that often gets asked is "should I be saving my graphics in PSD format instead of TIFF format?" PSD files are "Adobe Photoshop Documents" and offer no greater visual quality than TIF. The benefit of PSD, for Photoshop users is that the PSD format preserves Photoshop specifics inside the image like editable text, transparency, layers and other attributes.

PSD files are great for special projects but not so great for other uses, especially for those that want to archive old photographs in digital form. TIF files are a much better alternative because they can be opened by virtually any graphics editing application on virtually any computer. PSD files can generally only be opened by the Adobe Photoshop application.

And what of the Windows Bitmap (BMP) format? BMP graphics were once very common on Microsoft Windows systems, but the format was criticized for a number of limitations - some of which include large file sizes and poor interoperability with other computer systems. In fact BMP was used most often for digital wallpaper for computer screens ("desktop backgrounds"), and never caught on in the digital photography industry.

There's also the less common PNG format, which is a high quality format that uses a lossless compression method like the TIFF format. PNG is used extensively within the web design and Linux desktop communities, but isn't very common among the photography industry.

GIF is also another graphics format frequently found within the web design community. It has specific purposes but should never be used to save photos. General computer users should use JPEG or TIFF instead.

For submitting items to the newspaper, it is far better to send photos electronically whenever possible as JPEG or TIFF graphics. Attach them to an email and send them to us. That gives us a handle on quality control and makes it easier for us to ensure the graphics print the way they are supposed to.

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