Bob's Rock Shop: Technical Notes


Overview: The Attractions of Video Frame Grabbing

If you are already familiar with NTSC video and frame grabbers in general you'll probably want to skip ahead to the next section detailing hardware and software particulars.

All of the images of specimens from Bob's rock collection were generated using relatively inexpensive hardware and software to capture and process still images from NTSC video. The video frame capture techniques and hardware used offer several attractions besides low cost and can be applied to acquire image files of virtually any subject of interest to you.

NTSC (National Television System Committee) video sources abound. Unless you live in Europe where the video standard is PAL, every time you change channels on your TV, cable or satellite tuner you are switching among NTSC video sources. Your collection of video tapes and your VCR are an NTSC video source library. And if you own or have access to the use of a video camera or camcorder there is at your disposal an NTSC video source that can be used to acquire almost any image you might want.

The mind-numbing quantity and diversity of NTSC video images both archived and pouring anew at us every day present inherent attractions for documentary as well as creative work. The NTSC video signal standards were established in 1953. A lot of NTSC video has been taped since then. You've probably taped a little yourself. There's no shortage of raw material available as NTSC video.

The nature of the NTSC video signal itself (hereafter referred to as composite video or just video) offers certain attractions as an image source. Composite video is generated and transmitted in frames which are refreshed 30 times per second. These video frames are analogous to the image frames on old style photographic movie film. Each composite video signal frame can be converted to an image file with a hardware device that is generically known as a frame grabber. Combine your TV, VCR and/or camcorder with your personal computer, a low-end ($100-$200) frame grabber, your favorite paint programs and some graphics utilities, and you've got your very own digital graphics studio with which to work and play. You probably own most of this stuff already. A frame grabber ties it all together.

A significant advantage of video frame grabbing over conventional photographic methods of image acquisition is realized by eliminating the time and money spent in developing film, printing and then scanning. With video frame grabbing techniques the image file is generated directly from the video source. In studio environments, this allows for making very quick adjustments to video camera position, focus, lighting, subject orientation, background, etc. if the captured image indicates the need for such corrections. If you shoot video tape "in the field" that you later decide needs to be redone, you'll still have to go back out and shoot again. At least video tape, unlike film, is reusable.

Video tape offers an extremely cheap medium for storing images. If a single frame of composite video is captured as an uncompressed 640x480x24-bit color image file it will occupy 900,000 bytes or so. Viewed this way, a 90 minute VHS video tape stores the equivalent of 900,000 bytes/frame x 30 frames/sec x 60 sec/minute x 90 minutes = 146 gigabytes of images on about $3 worth of medium. Of course, you can't accesses a video image with a VCR and a frame grabber as fast as you can on your new $500, 1 gigabyte hard drive. But then again, you'd have to hook up a thousand of those 1 gigabyte drives to store the terabyte of images you can store and retrieve with your VCR, an inexpensive frame grabber and a handful of video tapes.


Making the Mineral Specimen Images: Equipment, Software and Techniques

The Camera

The video output from a Sony CCD-TR5 NTSC 8mm camcorder was used as a signal source to feed the frame grabber. A tripod for the camcorder proved to be a useful accessory. An indispensable feature of this camcorder for shooting rocks is it's macro lens which provides the ability to shoot very close-up to the subject. The image's depth-of-field is very shallow in macro mode and the small black and white LCD viewfinder of this camera makes precise focusing without the use of a monitor somewhat challenging.

Before an integrated studio was set up, several of the specimens were video taped with the camcorder in one location and frame grabbed off the tape later at a different location. While passable, the images that were grabbed off tape were generally inferior to those grabbed off the live video signal from the camcorder.

The Studio

A simple but effective studio for doing the mineral specimen shots was assembled on a couple of adjacent card tables. A piece of black poster board was employed as a seamless background. A piece of black spandex material was draped over it and used as background for several of the images. The most challenging problem with an indoor studio is the lighting. Getting enough light isn't the problem; getting the right color light is.

Reproducing the effect of sunlight indoors is not easy. Tungsten sources are too yellow, cool white fluorescents are too cool, grow lights are too red. Mixing different colored sources in various combinations can yield satisfactory results. Wide spectrum fluorescent bulbs are available but are not a panacea. Direct sunlight streaming through an unobstructed window is very nice to work with if you can arrange it. Of course you can always shoot outside in the sunlight but depending on your situation this may require you to record the shot and frame grab off tape rather than the undegraded live signal from the video camera.

A "spare" table-top color TV makes a handy video monitor to check and adjust the lighting and the camera focus if your video camera's built in monitor is lacking. A "spare" VCR is handy to have around the studio too.

The Captivator Frame Grabber

9-18-95 Update: VideoLogic has discontinued the Captivator (described below), citing unavailability of electronic parts discontinued by manufacturer as the reason. They do not have an immediate replacement at a low-end price point. You may still be able to find this grabber in stock at some catalogers and retailers. It's a shame to see this board disappear; at $100 it was a good value and an inexpensive introduction to frame grabbing and computer video.

The frame grabber used to capture most of images of specimens from Bob's rock collection is a 16-bit half size ISA card called the Captivator(tm) that's manufactured by Videologic. VideoLogic recommends an IBM or fully compatible E/ISA standard PC with a 33 MHz 386, 4 Mb ram and a 100 MB hard drive running Windows 3.1 as the minimum platform to support this card.

The Captivator(tm) card comes bundled with Microsoft Video for Windows(tm) and VideoLogic Videosnap(tm) software. It can frame grab 8, 16 or 24-bit RGB images from Pal as well as NTSC video sources with a maximum resolution of 640x480 pixels. It outputs image files in DIB and BMP formats. AVI format movies can also be made with this package. If you want to play with movies the faster your machine is, the better.

I've used this frame grabber with an older 386 SX as well as a new 486 DX4 and it functioned properly in both machines. Installation of the card and software was straight-forward and well documented. Mine cost just under $100. VideoLogic also offers some enhanced versions of this card, one of which has an NTSC TV tuner built in which should enable you to watch TV on your computer and frame grab right off the air. VideoLogic also offers high-end ($2000 class) frame grabbers. You can contact VideoLogic sales at 1-800-578-5644.

The Snappy Frame Grabber

If you're shopping for an inexpensive frame grabber you should consider the Snappy Video Snapshot(tm) from Play Incorporated. The minimum required computer platform is similar to the Captivator(tm) card. The Snappy can provide an impressive 1500x1125 maximum capture pixel resolution with 24-bit color. In my experience, the image quality suffers some in this high resolution mode, but that it can do this at all is somewhat of a breakthrough at its price point. It plugs into your computer's parallel printer port, eliminating the need for an open slot on your motherboard along with the potential hassles of getting a new board to coexist with everything else on your bus. It's what you might call "Plug and Play". 8-)

I've used the Snappy with a 486 DX4 and a plain vanilla parallel port on an EISA controller card and have had no problems with the hardware or the software. It comes bundled with Snappy Video Snap Shot software, which provides the fundamental GUI to the frame grabber as well as a number of luminance, color and filter controls. Also bundled is the Snappy edition of Fauve Software's Fauve Matisse, which provides more advanced image editing tools, and Gryphon Software's Morph.

The Snappy software outputs image files in BMP, PCX, TIFF, TGA and JPEG formats. This grabber doesn't do movies. It costs just under $200. The Snappy has received numerous favorable product reviews in various computer magazines. You can contact Play Inc. sales at 800-306-PLAY. They sent me a free promotional demo disk with some Snappy images when I called and asked for it. I like my Snappy. It does a nice job of grabbing video "stills".

Shareware Software

The Videosnap frame capture application that is supplied with the Captivator card was used to capture 640x480x24-bit BMP format stills from both video tape and the live video signal from the camcorder. Videosnap provides a scaleable live video image which can be used to monitor the video signal during image capture. Multiple captured images can be viewed simultaneously from within Videosnap. It also has the capability of importing DIB and BMP format files and converting Kodak PhotoCD images to DIB format.

The BMP format images output by Videosnap were further processed with a shareware bitmap editor, Paint Shop Pro(tm) 3.0 from Jasc, Inc.. This software requires a minimum platform of a 386 with 4 MB ram, VGA, a hard drive and Windows 3.1. Paint Shop Pro directly supports 26 different raster image formats and 9 meta and vector image formats. It is capable of reading additional formats with the installation of external import filters. Paint Shop Pro incorporates many useful functions for working with image files including an image file browser/manager, a screen capture utility, pixel level editing with an array of drawing, paint and select tools, color depth and palette management functions. It incorporates a number of standard and special effects filters and supports both user-defined filters and Adobe(tm)-compatible plugins.

Paint Shop Pro was used for cropping, resizing, and adding borders and text to the BMP format mineral specimen images. Most of the images were also processed with several of the image contrast and sharpness filters. After a satisfactory amount of puttering had been performed on each image it was converted with Paint Shop Pro to JPEG format. A zipped shareware version of Paint Shop Pro 3.0 (1.41 MB) gives license to a 30-day free evaluation. It costs $69 plus shipping for a registered copy and a manual.

Another shareware program available for puttering with image files and converting between formats is Alchemy Mindworks Inc.'s Graphic Workshop for Windows 1.1p. This one costs $40 plus shipping to register.

The comp.graphics Usenet newsgroup is a rich source for information on image files and software tools for manipulating them. If you haven't already read them, their FAQs provide an excellent introduction to image files and related topics.

Why Bob's Rock Shop uses JPEG Images

As you may have noticed, Bob's Rock Shop uses JPEG (Joint Photographic Experts Group) format images almost exclusively. The first iteration of specimen images for this project were done in GIF format with the idea of making them "universally" browsable. The use of the GIF format had two effects that I considered my "customers" would find unacceptable. Most of my fellow rockhounds are accessing the WWW just like I do, with a modem and a SLIP or PPP. The first bad effect was caused by the image file size that results from GIF compression. The 900 KB 640x480x24-bit BMP output by the frame grabber typically reduces to about 250 KB when compressed by conversion to GIF. 250 KB doesn't exactly transfer across a phone line in the blink of an eye with even a 28.8 modem.

The second bad effect is that the GIF format becomes even less attractive when you consider that most of its compression was achieved by reducing the 24-bit (16 million) color palette of the original BMP image to the GIF's 8-bit (256) color palette. That's not exactly "lossless" compression. All of the JPEG specimen images contain thousands of colors in their palettes. With JPEG, the 900 KB 640x480x24-bit BMP file output by the frame grabber can be compressed to about 25 KB or so before it begins to compare disfavorably on a visual basis with it's GIF counterpart. And of course the time required to move the 25 KB JPEG image over a phone line compares very favorably with the time required to move the 250 KB GIF. The reduction of bandwidth requirement is also good netiquette.

A major attraction of the JPEG format is that it does not dictate any particular compression ratio. The trade-offs to be made between file size and image quality are determined by setting a "quality level" control on the JPEG compressor software. Most of Bob's Rock Shop's large (640x480) specimen images are in the 25-50 KB size range. Future work in the rock shop studio will involve experimenting with even more aggressive compression ratios. The JPEG format was designed to achieve very high compression with realistic photograph-like images. There is a lot of confusion and misconception surrounding JPEG. If any of the above remarks concerning JPEG seem too good to be true, the Usenet JPEG FAQ is an excellent introduction.

Be sure and check out Netscape Navigator® if you're in the market for a freeware browser with built-in JPEG decoding and in-line viewing capability.


Rocks from Bob's Collection

Index of Specimen Images

Table of Contents

bkeller@rockhounds.com 8/3/95