Color horizontal resolution test?

[dpalomaki]

For kicks and giggles I thought I would do a quick test of color horizontal resolution of VHS. (Most resolution claims refer to a B&W image because that is what the eye sees best.) Resolution is usually spoken of as the limiting resolution where the adjacent bars (in this case green and gray) blend into a uniform wide bar.

I created a 720x480 chart of alternating green and gray vertical bars of various widths. The bars brightness were all about 43 IRE, the green hue was based on the green in SMPTE color bars. (The chart I used is attached as is a vector scope of it.) The chart provides sections of about 30, 38,45, 49,54, and 67 color lines. When compressed to half width about 60, 77, 90, 98, 108, and 135 lines. Because all bars were of equal brightness there was no B&W image change to support higher perceived resolution.

The chart was loaded into a NTSC 480i timeline in EDIUS X and output as s-video via a BMD Intensity Pro. The results were observed on a HITACHI HD TV operating in 480i, s-video input mode. I used a JVC HR-S3600 at SP speed as the VHS recorder (with VHS tape) and a Sony GV-D300 MiniDV for comparison. All I/O was via s-video except for a HDMI feed (from the Intensity Pro) to the TV was also tried. All signals were NTSC SD 4x3 aspect.

The observed limiting resolution observed are as follows:

HDMI - no loss of resolution observed (i.e., much greater than 135 lines)
S-video direct to TV: - between 108 and 135 lines.
S-video pass thru the JVC while recording - over 108 lines (but slightly less than direct to TV)
JVC VHS playback to TV via S-VIDEO - 45 lines

Sony MiniDV recording via s-video to TV - between 90 and 98 lines.

The 45 lines for VHS is no surprise, it is what would be expected thanks to the color under coding used by VHS. that limits color bandwidth to under 650 kHz.

The substantially higher resolution for MiniDV and direct s-video are also expected based on the higher bandwidth/sampling frequency used.

[themaster1]

So the good news is for hdmi as i understand it ?

[dpalomaki]

HDMI is a digital connection capable of lossless transfer of data. So it can be excellent, but it ultimately depends on how the video is converted from a live scene in front of a camera or a graphic in a computer to a format for HDMI transmission. and ultimate display on a monitor. The limitations and warts of each step in the signal path; e.g., hardware, software, media, connections, conversions, edits, etc., are cumulative.

[latreche34]

I couldn't quite understand the idea and the procedure of this experiment, I must be missing something due to age. Or maybe some screenshot of the results help clear the confusion.

[dpalomaki]

Typical video Resolution charts are based on image transitions from black to white and back; no color involved. The "Y" channel transitions between 7.5 and 100 IRE (for NTSC) while the "C" contains only the color burst.

I wanted a test where the "Y" channel remained constant (at ~43 IRE in this case) and the "C" transition between 0 saturation (no color) and a value short of typical SMPTE color chart green. This is shown in the two charts in the initial post.

The attached show a few screen shots of the HDTV screen taken with a cell phone showing the limiting resolution as the lines blur together. It also illustrates why colors blur and "go south" with successive generations of VHS copying. Electrically speaking the color bar is a pulse that quickly goes from a tall free standing skyline of buildings to piles of rubble as it makes successive passes through the low pass filter or VHS color under recording.

An academic exercise to better understanding of the effects.

[latreche34]

My point is wouldn't you use black and white test cards?

[dpalomaki]

Quote:

My point is wouldn't you use black and white test cards?

A black and white test card does not address the ability to resolve changes in color alone. It does address ability to resolve changes in brightness. My interest in this test was color only.