dyfan |
10-26-2009 01:07 PM |
Evaluating Elite's BVP4+
By Mark Goldberg
Quote:
In a perfect world, every professional wedding videographer captures technically perfect video images in the field Cameras-even the new digital video models-are always perfectly white balanced and always deliver images with just the right contrast range. They show deep rich blacks, bright but detailed highlights, and vibrant colors. In the "real world" we are far from that level of perfection. When we view a scene in the edit room numerous factors can lead to an image that does not match our impression of the original scene, or how we want it displayed on the finished videotape. The footage, in other words, may need some "doctoring" to achieve the proper look or tonal rendition we (or our clients) expect. And that's why every real world videographer will appreciate the abilities of a post-production processing amplifier.
Development of the BVP4+
The BVP4+ ($795 msrp) processing amplifier from Elite Video (501-321-0440; www.elitevideo.com) is a successor to the original BVP4 and provides several improvements over the earlier model The BVP4+ has 1200 lines of resolution while the original offered 800 lines. It also features adaptive resolution enhancement (which adapts the process to the characteristics of the incoming video) and a digital gamma compensator circuit, which is designed to boost highlight and shadow detail lost in the compression process of digital video. Both units were engineered and built in the US to the specifications of videographer and company owner, John Cooksey. BVP4+ Controls and Connections The BVP4+ is powered by an external 12-volt adapter block. It can also be operated from an external battery. The unit is approximately 15" deep x 3" wide x 3"high x 8" deep and is furnished with an instruction manual and a videotape. The front panel has four toggle switches including a herringbone filter (to reduce electrical interference noise), tint adjustment pass/adjust, tint adjustment range (+180 or -180) and black restore on/off The unit has nine knobs for controlling: split screen (compare before and after images), color level, flesh tone color adjust, tint adjust 0 to +180, tint adjust 0 to -180, point-to-point (PTP) luminance, IRE adjustment, resolution contour and black restore. On the back panel are switches for selecting composite or S-video in/out, analog or digital input, and Y/C or composite in/out. The BVP4+ has an all-metal, black case.
Inside are two circuit boards-one for the hack panel and a larger one for the front panel. Rear connectors are mounted internally to the rear circuit board, not the rear panel. In setting up the unit for evaluation, I found these connectors to be a tight fit with my S-video cables-tight enough to temporarily distort the circuit board during installation.
Test Setup and Evaluation
I used the JVC BR-S500 S-VHS Edit Desk player (with TBC) as a source, and JVC's BR-S800 as the editor. A JVC JX-5V55 video editing processor was bypassed, but was standing by for comparison. To complete our test set-up we also connected a Panasonic digital mixer, a Videonics Powerscript character generator and a JVCTM-1400 monitor. The signal path was C throughout. The instruction manual recommended connecting the BVP4+ downstream from a digital mixer and upstream from a titler. Initially I followed that recommendation and placed it between the mixer and CG. while this was effective in controlling scene brightness and contrast, the results had a posterized look resulting from the signal quantization that occurs in a digital mixer. Black noise was also excessive. It was too easy to send the signal into instability. To me, the result of this hookup was technically unacceptable. I reconnected the BVP4+ between the player and the JX-5V55 editing processor. The JX-5V55 has been around for eight years, but I still find it useful for adding black or colored borders and mixing stereo audio sources. It also provides two levels of color correction, fades, effective black stretch and enhancement. My digital mixer is downstream from the processors. This seemed to be a more logical connection because it allows the BVP4+ to work with more signal levels--an advantage for an analog domain processor. The results we obtained were far superior to the after mixer connection.
Basic Operation
Both the users manual and the video tape recommend using the controls sparingly, which we found to he sound advice. All controls offer extremely wide latitude, enough to send the video signal into instability at either the black or white. I liked the variable horizontal position of the split-screen, which allowed me to center it over an item of interest for a good comparison. The color level was a very tempting control, one that added a "Kodachrome" saturated look to the original image. What looked nifty in the original playback and edit master, however, gave a somewhat exaggerated color in the release video, so one must be conservative in the use of this control.
The manual suggests using the BVP4+ at the release tape dubbing stage because of the unit's excellent signal-to-noise ratio and near-transparency, but I recommend conservatism here as well. This control can also be used to eliminate the color and create a B/W image. The flesh tone control is more subtle than traditional proc-amp hue controls. Remarkably, it allows adjustment of flesh tones with minimal effect on other colors. In transferring photos to video, I found it particularly useful for eliminating color errors and blueness from a camera flash. The tint adjustment was less intuitive to operate than the joystick color controls found on the JX-5V55 and the Panasonic digital mixers. In operating the tint control, you must first toggle the pass/adjust switch to "adjust," then select the +~80/-180 range based on the color shift desired, and finally adjust the appropriate knob. This adjustment had little affect on the blacks or whites, unlike many proc-amps that shift all colors in the scene. Its range was narrower than other proc-amps I have used. The PTP luminance control affects dynamic range (the span from darkest to brightest), and the IRE adjustment appears to uniformly affect all video levels rather than just raising the black level. These two features are interdependent and offer a great range of control. Over-processing at either end (black or white with either control) could send the video signal into instability. The result could he rolling, tearing and even some bizarre side shifrs when going through digital mixers and CGs like the Powerscript. Compared to the image enhance function I have used on other processors, the BVP4+'s resolution control worked with minimal artifacting, and without the outline-effect typical of less sophisticated systems. Again, one must guard against over processing, because it will enhance inherent image noise as well as desired detail and becomes even more exacerbated if gain-up was used during the original recording. However, this control was clean, effective and relatively artifact-free when used with a well-exposed image. The black-restore function is unique to the BVP4 series and effectively sets selected luminance values to black. The best way to visualize this is with titles on a black background which would otherwise show as a gray hue with PTP or IRE adjustments. If over-applied, the images take on a partially black posterized look. In use, one must start from zero and gradually increase the level until the effect is barely noticeable. The range of control afforded by the three tonal adjustments (PTP IRE, black restore) allowed me to recover some severely under-exposed video, which helped rescue video from a low-light wedding scene. This recovery could not match properly exposed video, but at least it made the image recognizable since boosting the black level also boosted the part of the image containing the most luminance noise, I did not use the resolution contour. (I have set up a special web page of these example images at http://www.markgoldherg.com/bvp4plus.) One quirk of the black restore function occurs when the herringbone filter is on. Normally, this filter is used to reduce interference in the image caused by nearby electrical devices, such as motors. The interferenc47e appears as diagonal lines. If the filter is on, the black restore effect diminishes at the top and bottom of the image probably due to the inherent 60Hz filtering. This was confirmed in my conversation with Cooksey, who advised keeping the filter off unless absolutely needed. The user's manual provides a good discussion of operating features and functions. There's a one-page "cookbook" covering four examples of uses: making a B/W tape from color, restoring faded color, making dupes, and making third and fourth generation tapes. There are no image illustrations in the manual, hut the video certainly has them. The manual gives such directions as, "Reduce the color level by 10-20%," hut there are no numerical markings on the controls, just radial lines. There is also a brief question-and-answer list about internal functions of the unit and a discussion of how to make adjustments for using the unit in conjunction with large monitors. The manual also includes caveats for coping with the particulars of other ubiquitous gear such as the Videonics MX-l and the Panasonic AG-456 and AC. 1970.
Using the BVP4+ with Digital Video
The advent of digital video for acquisition will have many of us wondering about the role of a processor that still operates in the analog domain. Cooksey says, "The fact that a signal is digital does not necessarily mean that it has good color and dynamic range. The analog pass-through can be worth the iniprovements. Even when going to NLE, the BVP4+ works in real time, while the filters in NLE software require extra rendering time.
In Summary
In exchange for the wide control range afforded by the BVP4+ there is a danger of producing an edit master that looks good but ultimately yields unacceptable release videos that have over saturated noisy color or even image disLortion or instability. There is no safeguard or level indicator on the unit to prevent this or to warn you when IRE levels are outside of NTSC specifications. I recommend individual testing by going through all the generations you anticipate. For serious professional applications, checking the setup with a waveform monitor and vector scope is strongly advised. For any level of processing, the BVP4+ required both practice and restraint. Ergonomically, I would like to see numbering on the control knobs to allow for greater precision in making and noting the settings. Mechanically, I'd like to see the circuithoard-mounted video connectors replaced with bulkhead-mounted equivalents to prevent damage that might result from an overly tight cable fit. I was impressed by the BVP4+'s excellent technical performance and signal-to-noise ratio. If controls were set to zero, there was effectively no change. In other words, the unit provides a clean pass-through. The controls offered a wide range of adjustment in an innovative way. The unit's recovery of some of my previously unusable dark video was dramatic. Both the user's manual and the included instructional video were packed with lots of helpful information and examples. In the range of my testing, the BVP4+ performed equal to or better than the claims and illustrations in Elite's demonstration tapes. Even though it is not as intuitive to operate as traditional video proc amps, the BVP4+ offers special capabilities. It is a piece of home-grown technology, developed specifically for the wedding video industry, that will give you much greater control over the post-production quality of your images.
|
--------------------------------------------------------------------------
So: Does anyone have the owner's manual who could post the details on how one internally adjusts to remove the vertical line/patch area that shows up in the right-hand over scan area?? If so, thank you in advance!!
|