MU LTIM EDI A L A B AMSTERDA M
ACURSUS
DOCENT
Photoshop-B
Angelo Spiler
In this tutorial the essential web and print formats are described, when you should use them, and when not. PSD - A PSD file is the proprietary layered format used by Adobe. It stands for Photoshop Document and is designed to save and take advantage of all Photoshop’s possibilities, such as layer blending options, alpha-channels etc. BMP - Bitmap files were developed by Microsoft as an uncompressed image format. Being uncompressed, the files are typically much larger than other common file types. GIF - Graphics Interchange Format images are a form of bitmap files designed to be much smaller. Using compression and the limitation of only 256 colors, GIF images are well-suited for use on the internet where speed can be an issue. GIF images also support animation by setting up seperate frames, each with their own color pallete, and then play them in sequence. Because of the limitation to only 256 colors GIF’s aren’t well suited to represent photo’s on the web. EPS - Encapsulated Postscript files support a combination of vector graphics and bitmaps, initially used by Adobe Illustrator. Photoshop, however, rasterizes the vector graphics converting them to pixels. EPS fles come in a variety of types. EPS is similar in its limitations to the TIFF format, including the requirement to flatten all layers. It is also possible to apply JPEG compression however this can cause unknown effects called artefacts. JPG, JPEG, JPE - Perhaps the most common file format for digital photographs, JPEG offers a relatively small file size thanks to its lossy compression system. Joint Photographic Experts Group is only the way in which the images is tranformed into data. This format does not perform well for line graphics or charts, but rather photographs where the compression blends in with the textures. High compression can, as with GIF’s, result in artefacts. PSB - The Large Document Format for Photoshop is designed for images with dimensions greater than 30,000 pixels in both dimensions and up to the maximum 300,000 pixels in either dimension. This is a native Photoshop format is not supported by many (if any) other programs. The large document format is also one of several formats that allows 48-bit images (3 16-bit channels instead of 8-bit). PSB files support a majority of the PSD features and are essesntially the same except with support for large files. PDF - A Photoshop PDF, or Portable Document Format, is a specialized PDF designed by Adobe for Photoshop. Similar to both Acrobat PDF’s and Photoshop PSD’s, this format supports many of the features of both programs: transparency, layers and vector graphics. Photoshop PDF’s primarily use the CMYK color scheme. It is used by Adobe’s InDesign and being a PDF, it is viewable in Acrobat. This format features the security of locking the file from
RH – 30-07-09
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editing. Suitable for print (high-res) and web (low-res). Most print companies nowadays ask for ‘certified PDF files’ which are files digitally checked for errors. RAW - The Photoshop Raw format enables support for various camera’s raw image type. This allows greater control over the quality of the image. The problem with this format is its lack of support by many programs. This is caused by the fact that the image is not processed at all (or ‘not cooked’). The information captured by the camera’s sensor is exactly what makes up this file. Support for this format is growing, but the exact format varies between manufacturers. DNG is another popular raw format which is literally a digital negative of the image. PNG - Portable Network Graphics is a format designed to replace the GIF using superior technology. It has support for many of the GIF features but also includes transparency. It has surpassed the GIF in many areas, the most common being color depth and transparency. The color depth of a PNG is extended up to 48-bit and the transparency uses a much broader range of options in order to bring about the required results. PNG images are usually large files because of the higher quality they have compared to either GIF or JPG. This is due to the lossless compression used by. Support for PNG images is slowly growing. All of the modern webbrowsers support viewing PNG’s, but the lack of animation is hindering further growth especially in regard to advertising on the web. TIF, TIFF - Tagged Image File Format is a common high quality image file used mainly by photographs and detailed designs. Supported by almost all major image editors, TIFF is a flexible format that can be used in cameras, scanning, printing, and design. TIFF offers the ability to archive and store with JPEGcompression, bitmaps and vector graphics. But this format also supports compression in a lossless format and images can even be edited and resaved without any loss in quality. Too big and thus not supported for webpages and not as many saving options as PhotoShops PSD-format.
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