How to Do Everything With Your Scanner- P31 ppt

FIGURE 8-3 Extensions for some common image formatsSelecting an Image Format You don’t have to specify a format when you save a file.. If you don’t specify a format when saving a file, t

FIGURE 8-3 Extensions for some common image formats

Selecting an Image Format

You don’t have to specify a format when you save a file The image-editing program will automatically do it for you Image-editing programs such as PhotoSuite, PhotoDeluxe, Paint Shop Pro, and Photoshop save files to their own native format as a default

If you don’t specify a format when saving a file, the program you’re using will save the file in its proprietary format Using only the proprietary format will work fine for you if you want to edit, save, and print files using the same application, as many people

do You also need to be reasonably sure that anyone you send your images to can open them in the proprietary format Also, some file formats allow you to save special effects, such as layers of text or graphics over a photo, that other formats do not

Although you can accomplish many tasks using only the default proprietary format, you can sacrifice efficiency by staying in a file-saving rut You achieve versatility and make life easier by choosing the appropriate format for the task at hand For example,

if you’re sending a file over the Internet, you most likely want to opt for a format that economizes time and space by compressing data If you’re giving an image disk to a

GIF image format

JPEG image format

friend who doesn’t have a copy of PhotoDeluxe, he or she won’t be able to open the image if you’ve saved it in the default proprietary format (PSD) for PhotoDeluxe

This section familiarizes you with some of the most commonly available and useful image formats It also gives you a few pointers on how to select the one that best meets your needs

JPEG: The Most Common Internet Format

The main advantage of the JPEG format is that it provides you with the ability to

eliminate image information to reduce file size This process is called compression.

The advantage here is that smaller files transfer more quickly over the Internet

Unfortunately, overcompressing a JPEG file can significantly reduce the detail

presented in an image The more a file is compressed, the more image data detail is eliminated

If you save a photo in JPEG format and later want to make changes to

it, rather then editing the JPEG file, rescan the photograph and make changes to the scan This minimizes data loss.

GIF: The Graphics Interchange Format

The graphics interchange format, or GIF, is another type of format well suited for transferring files over the Internet It’s a file type designed for efficient compression, and also supports animation PhotoSuite allows you to create animated GIF files, as explained in Chapter 17

GIF is a favorite format because of its lossless compression scheme, which deletes

only redundant data This type of compression doesn’t degrade image quality of the finished product GIF is perhaps the most widely used format on the Web

PNG: An Alternative Graphics Format

The PNG acronym stands for portable network graphic This file type is an alternative

to the GIF format It also uses a lossless compression format

There are times when PNG can be more desirable than GIF for two reasons First,

it is one of the only formats that allows you to save more than 256 colors It uses a compression scheme that doesn’t degrade the quality of the image files

As you can imagine, this format produces large files because there are lots of color data and a compression scheme that retains a considerable amount of quality

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TIF: A Very Portable Format

The tagged image file, or TIF, format was developed by Microsoft and Aldus It is a widely used format, which makes image files saved in this format very portable from application to application It handles grayscale, 8-bit, and 24-bit color, and is compatible with a wide range of software programs This makes it a good choice for swapping files among different image-editing programs, and sharing them among friends and family on a disk or CD It’s not, however, the format of choice for sending things over the Internet

TIF compression does not reduce file size by very much, but this means it also doesn’t result in a lot of data loss In a nutshell, with the TIF format you get good image quality, but files that are a bit unwieldy for transferring over the Internet

BMP: The Most Versatile Format

Windows bitmap, or BMP, is the native file format for Windows graphics Every Windows-based software program supports this format Unfortunately, this format does not support compression You also cannot save more than 256 colors using this format

The Costs and Benefits of Compression

Compression is the process of compacting data to save space When I think of file

compression, I always think of those packets of dehydrated food they sell in the camping stores In both processes, you don’t store what can be easily replaced: water

or repetitive data

How Compression Works

There are many forms of compression, but most of them work on a principle of identifying patterns of repetitive or similar data The repetitive stuff is coded, rather than stored The data that is not stored is either lost or replicated when the file is subsequently opened

How much data you eliminate depends on the compression ratio that your

image-editing program uses Some programs, such as Photoshop, allow you to specify a compression ratio when saving a file to certain formats PhotoSuite and PhotoDeluxe automatically determine the compression ratio for you The higher the compression ratio, the smaller the file size and the more data is lost

Compression Techniques

There are two types of compression: lossy and lossless Lossy is very aggressive in

discarding image data to reduce file size Initially, the impact of this lossy compression isn’t too devastating, but over time it takes its toll

If you repeatedly save a file using a lossy compression scheme such as JPEG, each time you do so you recompress the file, eliminating more image data Generally, the data loss isn’t apparent to the naked eye If you keep recompressing a file, however, you eventually might end up with odd effects such as a light border around a dark area

in the photo, or a fuzzy image If you’re producing high-quality graphics for offset printing, you might notice these effects after only a few compressions Figure 8-4 shows some effects of compression on a JPEG file that’s been saved multiple times

FIGURE 8-4 A 121KB JPEG image that has been saved 25 times

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A lossless compression scheme discards only redundant data, which is data that’s not actually used in producing the image More importantly, data isn’t lost each time you open and save the file The disadvantage of lossless compression is that it’s much less effective in reducing file size The TIF format uses a lossless compression scheme Figure 8-5 shows a TIF image after multiple saves It is sharp and clear, but the file is about two-and-a-half times the file size of a similar JPEG image

FIGURE 8-5 A 3.3MB TIF file that has been saved 25 times