Publishing Schematics and Board Layouts on the WEB

Introduction

Until a couple of years ago, if a customer or vendor needed to look at one of your schematics or board layouts you printed or plotted out a page or two and Fedex’d it to him. Today, you are likely to get a request to email it or to load it on your WEB server so the client can look at it or print it out locally. The WEB can make cooperative design from thousands of miles away a much faster and less expensive process but you’ll have to be able to quickly and effectively get your proprietary data into WEB standard formats.

This paper will discuss how to do that and will cover:

    WEB Graphic Formats

    Bitmaps vs. Vector

    Resolution vs. File Size

    Conversion Tools for PCB to WEB

Native WEB Browser Formats

One tenent of the WEB is that you cannot really control what is going on at the other guy's station - you don't know which browser he has, what platform he's running on, how large his screen is, how many colors he can support or how fast is his connection. But there are a few assumptions you can make that are very, very safe.

The other guy's browser has native support for at least two bitmapped graphics formats:

    GIF - GIF (graphics interchange format) is a compressed bitmap developed by Compuserve for their network. It is well supported by even the oldest WEB browers and most desktop publishing tools. GIF compression uses the LZW algorithm which is patented by Unisys. GIF can support 24 bit color using a maximum of 256 color palette. Maximum size is 64K x 64K pixels One downside to GIF is that after years of inactivity Unisys is attempting to enforce the LZW compression patent; a few applications developers have considered dropping GIF.

    JPEG - JPEG (Joint Photgraphic Experts Group) is another compressed bitmap format; it can achieve higher levels of compression for complex images but it is a lossy compression so the uncompressed image is no longer identical to the source image. It is most applicable to for images with many colors and much variation - photographs of people or landscapes. JPEG is not really suitable for schematic and board layouts so we will not discuss it further in this paper.

Plug Ins for Other Formats

Your browser can interpret and display additional formats by using support software - either as “plug-ins” or as “helper applications.”. Plug-ins and helpers are available for a wide range of graphic file formats including:

    EPS (encapsulated Postscript

    PDF (Adobe’s Portable Document Format)

    DWF (AutoDesk’s Drawing Web Format)

Plug-Ins and helper applications may be freely distributed or they may cost money. They may be available for only a few platforms or for many platforms. When you decide how to post your schematics and layouts you must consider both the cost and availability of a proprietary plug-in or helper. A severe limitation for the majority of plug-in's is that they do not support a wide range of platforms. Many are Windows- centric and in fact may only work on some versions of Windows and not on others. Since much industrial strength PCB software is designed on UNIX we rejected all plug-ins that weren't available on:

    Windows - UNIX - Macintosh
Adobe's PDF plug-in is both freely available and runs on all of the aforementioned platforms. In fact, we decided that this plug-in is so good that it merits consideration as the best way to display your schematics and board layouts on the WEB.


Pros and Cons of Using GIF

Schematics and Board layouts can be saved as GIF files so they can be viewed and plotted from the WEB. This is a very straightforward approach but it does have some serious pro's and con's. Below we've summarized what to look out for.

PRO

100% Support - you are 100 percent sure that anyone with Netscape, Mosaic, Spyglass, Microsoft Explorer of any version can read GIF. No additional configuration or software installation needed.

Multi-platform - of course since GIF is native to the browser it is supported on any platform the browser supports.

Easy to Produce - the GIF spec is well documented and there are many commercial, shareware and freeware tools that read/write GIF. GIF is extremely easy to generate from screen captures.

CON

Optimum for Small Image Area - GIF is ideal for small images at screen resolutions: for example a 3 x 3 inch aimage t 72 dpi. Detailed schematics and board layouts generally require higher resolutions of 150 to 300 dpi and page sizes can range up to 24 x 34 inches. The GIF file gets very large under those conditions and many GIF viewers may choke loading such large files.

Print Quality - a GIF file with dpi that looks good on screen will not print very sharp on a 300/600 dpi laser. If one goal is to enable your customer to print out copies for himself bitmap resolutions either have to be higher resulting in larger files.

Dumb - GIF files can't be scanned by spiders or other automatic indexing software to see what's inside of them. A PDF file for example, can have the name of the part, dates, etc... in text format that can be indexed. This may prove to be extremely important in the future.



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