Identifying Common Tape Defects for Commercial Video Restoration
It’s everyone’s worst nightmare; you put the tape into the deck knowing you have one or two chances of capturing a fragile tape. You cross your fingers hoping it’s going to look OK… it doesn’t! Don’t worry though because all is not lost!
Even some of the worst tape faults can be fixed and I will be identifying some of the more common issues you will come across and provide some hints and tips as to which tools to try inside of PFClean’s Telerack and Workbench that can help make your video artefacts disappear post capture. So let’s fast forward…
Back on Track with Telerack
One of the features of PFClean is the powerful Telerack video restoration engine. With an emphasis on speed and a focus on the most common defects, this is an ideal way to restore tape based media especially in cases where fast turn around and large volume of media is involved. Below is a list of common tape faults with examples along with tips of how they can be identified and how they can be easily fixed in Telerack.
These mainly present themselves as a horizontal line sometimes teardrop shaped, usually bright that pops on screen for one or two frames that can be staggered in intensity. Occasionally these can be persistent through an entire tape.
Like dropout but larger and with greater frequency, with a band of colour or misregistered image lasting no more than a frame usually. A common site on old and worn analogue tapes.
Timebase Corrector Dumping
Sometimes referred to as a bump, this problem presents itself as brief shift in Image position normally vertically and can range from very mild to very severe.
Excessive Tape Noise
Tape noise will appear heavy in tapes that are multiple generations away from the original source and/or have started to deteriorate with age. Additionally material that originated on legacy camera systems can be susceptible to excessive noise do to their low sensitivity.
High chrominance areas can lack fidelity, especially where the source is 4:1:1 or 4:2:0. Most noticeable in areas of red along diagonal surfaces. Formats such as MiniDV, DVCAM, DVCPRO and HDV all suffer greatly from a lack of chroma information.
Chroma fringing can appear in high value chrominance and specular detail, this is caused by crosstalk in the luma and chroma signals. Next time you watch an old television series watch areas of high detail and you might notice a coloured shimmering, this is chroma fringing.
Appearing as light or dark bands horizontally across the image lasting over a number of frames. Rapid changes in luminance within a scene can sometimes exacerbate this problem.
Flickering, Scratches and Dirt
Tape material that has been telecined from 16mm and 35mm can suffer all the artifacts that originate in the original film elements. Typically archive material that’s been transferred to tape suffer from excessive dirt and scratches.
Minor variances in luminance values between scanlines. Sometimes caused by variences in field luminance. Not to be confused with rolling bands, these can be particularly troublesome to fix without dedicated effects.
Precision when you need it
The Telerack is focussed on high performance video restoration. Ideal for the hours and hours of tape that can be found in archives. However, some fixes are so severe they require the precision that can be found in PFClean’s powerful Workbench. In the table below we will help you identify these severe faults and suggest a Workbench tools to help you restore your tape.
Momentary Head Clog
Thick horizontal band or sometimes entire frame of misaligned and warped image, usually for a single frame. The distortion can be complex and requires the rebuilding of a portion of the frame.
Common in formats such as 2" Quad and TypeC where the physical tape is exposed to the environment. This artefact presents itself as a thin horizontal line of misregistered image that remains static and constant for the duration of the scratch. In a way very similar to a film scratch but horizontal.
Transverse Tape Damage
Horizontal band or misregistered image that rolls up the screen usually from bottom to top. This is a fairly common fault in old analogue tapes. Next time you watch an old VHS lookout for this fault.
Capstan Servo Off-Locks
Brief moments of picture instability and sometimes picture breakup along with wow distortion in audio. Normally this is seen at the top or bottom of the screen.
Mild Tape Mistracking
Appearing as a thin band at the very top of the screen with segmented or misregistered image. Can be fairly constant if the tracking was not adjusted correctly during the capture.
Severe Tape Mistracking
Breakup of the entire image resulting in multiple dark and light lines with bands of misregistered image, flickering, and loss of colour. Possibly the most complex error you will encounter and most difficult to fix. Sometimes this is why it is useful to have a dub of the tape even if it is lesser quality so that it can be used to rebuild the images.
Lifted blacks caused by transfer errors in the dubbing process. Sometimes this can occur when standards converting from one region. NTSC originated material can look milky on PAL systems if not properly converted.
Chroma Phase Convergence Error
Can be observed via a vectorscope and waveform where chroma phase is out of alignment. In the example above, this was caused by material from one tape being spliced into the master without correct calibration.
Blocking and Compression Artifacts
Highly compressed formats such as mini DV can suffer macroblocking and image breakup during high dynamic and kinetic shots resulting in squares and mosquito noise around detail.
Luminance/chroma trails appear in bright highlights and chroma; this persistence is where the luminance value has not had time to reset to zero causing a ghosting trail or comet. Common in material recorded using cathode ray tube cameras from the 1930s to 1980s.
Horizontal and Vertical Sync Pulse Loss
This particular error shows up as a merging of the adjoining frame with Vertical or a horizontal breakup in image. If this error occurs it’s normally accompanied by one or more of the errors described above on the surrounding frames.
Wait! It’s Not the End of the Tape Yet!
Next time you watch one of your favourite vintage television shows, films on VHS or a family movie shot on tape, lookout and see if you can spot any of the tape faults I’ve mentioned, you probably will be able to spot more than you think…
Video tapes have recorded some of the most important moments in our history and deserve the care and attention to make them shine.
Sony has a great page here showing their milestones in broadcast history from the early 1950s through to modern day.
In my previous article about the Russian archive, I talk about some of the titles captured from tape.