Graphics concepts Technical Writers should know… G.M. Sundaram KBuffer, Chennai

Graphics concepts Graphics concepts Technical Writers should Technical Writers should

know…know…

Graphics concepts Graphics concepts Technical Writers should Technical Writers should

know…know…

G.M. SundaramG.M. SundaramKBuffer, Chennai.KBuffer, Chennai.

16 Februay, 2008 The Chennai Technial Writers Meetup 2

Graphics concepts Technical Writers should know…

Points to ponder over…• Graphics can be deployed for

effective communication• Appropriate Graphics file formats to

be used• File size considerations to be borne

in mind



Points to ponder over…• Should not distract the reader

because in that case the purpose is lost.

• Last but not the least is the cost consideration. Is it worth the time and cost involved?



For Print media or Electronic media?



Some common file formats.bmp bitmap .psd Photoshop

document.pdf Portable Document

Format

.pic picture .wmf

Windows Meta file

.dxf Autocad Interchange File

.gif Graphic interchange file

.dwg AutocadDrawing .cgm Computer graphics metafile

.eps Encapsulated Postscript

.cdr Coreldraw .emf Enhanced Meta file

.jpg Joint Photographers Expert Group

.flm Filmstrip .fh(*) Freehand Drawing

.pcd Kodak Photo CD .png Portable net graphics

.svg Scalable vector graphics



Lossy Vs. Lossless Compression

You might have heard of the terms "lossy" and "lossless" compression.

Lossy method: Lossy algorithms accept some degradation in the image in order to achieve smaller file size. A lossy algorithm might store color information at a lower resolution than the image itself, since the eye is not so sensitive to changes in color of a small distance.

JPEG (Joint Photographic Experts Group) is an ISO/IEC group of experts that develops and maintains standards for a suite of compression algorithms for computer image files.

Want to dig deep into this concept? Follow this link:

http://en.wikipedia.org/wiki/JPEG







JPEG level 12 Highest quality File Size: 210 Kb

JPEG level 8 Medium quality File Size: 89 Kb

JPEG level 4 Low quality File Size: 61 Kb JPEG level 0 Lowest quality File Size: 44 Kb




Lossless method: A lossless compression algorithm discards no information. It looks for more efficient ways to represent an image, while making no compromises in accuracy.

A lossless algorithm might, for example, look for a recurring pattern in the file, and replace each occurrence with a short abbreviation, thereby cutting the file size.



Tag Image File FormatThis is extensively used in high quality printing. TIFF is, in principle, a very flexible format that can be lossless or lossy.

The details of the image storage algorithm are included as part of the file. In practice, TIFF is used almost exclusively as a lossless image storage format that uses no compression at all.

Most graphics programs that use TIFF do not compress the file.

Consequently, file sizes are quite big. (Sometimes a lossless compression algorithm called LZW is used, but it is not universally supported.)



Tag Image File FormatTIFF (Tagged Image File Format) is a standard file format designed to promote the interchange of digital image data. TIFF is a 24 bit, raster data, lossless format, used chiefly to store the "master" copy of images used in desktop or photo publishing.

TIFF images are of high quality, but like PDF, have no drilldown or popup capability. TIFF images are not compressed.

However, they usually compress well using LZW or ZIP compression methods (available through save options within most graphics manipulation programs).

TIFF images can not be viewed from a web browser, and must instead be viewed from a graphics manipulation program, such as Adobe PhotoShop. They cannot be embedded into a web page.



EPS File FormatEPS (Encapsulated PostScript) is a standard file format for importing and exporting PostScript files. An image in this format is essentially a single page PostScript file that describes the image.

The EPS format is very similar to PDF, and consequently images in EPS format are of the same size as images in PDF. They are of very high quality, but like PDF, have no drill-down or PopUp capability, and can't display transparency.

The main purpose of an EPS file is to be included in other pages. EPS images can not be viewed from a web browser, and must instead be viewed from a graphics manipulation program, such as Adobe PhotoShop®. They cannot be embedded into a web page.

EPS capabilities are not intended for most users. Suitable for line arts and logos.



PNG File FormatThe PNG (Portable Network Graphics) format is a lossless image format similar to JPEG, but higher in quality (they can contain more than 256 colors) and much smaller in file size. Their file size is slightly larger than FLASH and significantly larger than SVG, however their quality is significantly less than that of both formats. PNG images print only at a low resolution of 72 DPI.



EMF File FormatEMF (Enhanced Meta File) is a vector-based image format designed for and popularized by Microsoft Windows. EMF images are of high quality, but like PDF, have no drill-down or PopUp capability. They also do not support transparency.

EMF files are typically between 5 to 10 KB in size.

EMF images can not be viewed from most browsers, and must instead be viewed from a graphics manipulation program, such as Adobe PhotoShop. They cannot be embedded into a web page.



Do you where are these from?



GIF File Format

GIF creates a table of up to 256 colors from a pool of 16 million. If the image has fewer than 256 colors, GIF can render the image exactly.

When the image contains many colors, software that creates the GIF uses any of several algorithms to approximate the colors in the image with the limited palette of 256 colors available.

Better algorithms search the image to find an optimum set of 256 colors.

Sometimes GIF uses the nearest color to represent each pixel, and sometimes it uses "error diffusion" to adjust the color of nearby pixels to correct for the error in each pixel.



GIF File Format

GIF achieves compression in two ways.

First, it reduces the number of colors of color-rich images, thereby reducing the number of bits needed per pixel, as just described.

Second, it replaces commonly occurring patterns (especially large areas of uniform color) with a short abbreviation: instead of storing "white, white, white, white, white," it stores "5 white."

Thus, GIF is "lossless" only for images with 256 colors or less. Do NOT use GIF for photographic images, since it can contain only 256 colors per image.


File Format Where to use Do not UseTiff This is usually the best

quality output from a digital camera. Use it for high quality printing

Do NOT use TIFF for web images. They produce big files, and more importantly, most web browsers will not display TIFFs.

JPEG Use for all photographs on the web

Do not use it for high quality printing unless you are having a very high resolution or actually reducing the size. Never use this for line arts


Which format to use? Don’t resort to tossing!


File Format Where to use Do not UseRAW Use this for digital

images.Do not use it for Web images or for Printing

GIF Can use it for images of 256 colors or less. The files will be small yet perfect.

Do not use it for printing. Do NOT use GIF for photographic images, since it can contain only 256 colors per image.




File Format Where to use Do not UsePNG Use it if you have an

image with large areas of exactly uniform color, but contains more than 256 colors, PNG is your choice. Its strategy is similar to that of GIF, but it supports 16 million colors, not just 256. Best choice for Web photographs.

Unfortunately, Microsoft's Internet Explorer does not properly support PNG transparency, so for now web authors must avoid using transparency in PNG images.

EPS Best for line arts, and Vector images. Can be used for high quality printing

Not available for the web. Of course, you can use ADDsee and view it.





Scanning TechniquesSame image scanned in different modes

24 bit image with 16.7 Millions of colors

Grayscale – 256 shades

Line Art – only two colors

scanned as Grayscale, and was then dithered to 2 color B&W



Scanning TechniquesSame image scanned in different modes

Line art mode is ideal for pages of printed text, which might look like this. This is 12 point text scanned at 300 dpi from a magazine. It would appear normal size when printed on the printer especially when you use OCR.

Halftones - this scanner mode is for images to appear in magazines and newspages. Our printer drivers provide default halftones that are normally used instead. This is a 4x4 halftone screen, and it needs a much larger image, matching the Line art printer resolution at 600 or 720 dpi to look right. Instead, it's only 50 dpi here for the video screen size.



Some technical terms explained…

Halftones - An image reproduced through a special screen made up of dots of various sizes to simulate shades of gray in a photograph. Typically used for newspaper or magazine reproduction of images but it is also how today's inkjet printers work.



Some technical terms explained…

Line Art - A graphic image drawn only as lines without any filled-in color or shading.



Checklist for printing

1. Include all the support/image files

2. Support files are all image and graphic files imported into your document. If support files are missing, graphics may remain visible but will output in low resolution.

3. Ensure you supply high resolution, original, and editable copies of all graphic files.

4. Supply the necessary fonts, both printer and screen fonts.

5. Convert all colors from RGB to CMYK.

6. Scan and save your images at the correct resolution.



Checklist for printing continued

7. Set scanning resolution at double the output line screen. Suppose the printer print at 175 line screen, so scan resolution is at 350 dpi (dots per inch) or higher.

8. Set up bleeds correctly.

9. If your artwork requires to print color all the way to the edge, please extend one-eight on an inch beyond the size of the finished document.

10.Print a mock-up of your document. A mock-up is a guide for printing to how the finish of an artwork is going to look like. Even a laser proof will be helpful.

11.Label your CD or zip or pen drive appropriately.



Thanks for all the patience and this magnificent opportunity!Any questions can be forwarded to:[email protected] post a shout at the Meetup site and feedback to me

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Graphics concepts Technical Writers should know… G.M. Sundaram KBuffer, Chennai