Snell & Wilcox SW2 and SW4 "Zone Plate" Test Chart (also referred to as Snell & Wilcox Test Pattern) were
TV test cards introduced in the 1990s and used with
NTSC,
PAL and
SDTV systems.[1]
They were created using equipment like the Snell & Wilcox TPG20/21 Test Pattern Generators.[12][13]
Features
The Snell & Wilcox Test Chart #2 (or SW2) is used for general adjustments of video processors, mixing equipment, and display devices such as
CRT TVs and
projectors. Main features and tests allowed by the chart are:[12][14][3]
Circular grayscale (to check for dither or quantization problems)
Chart format
Registration check (for color alignment check)
Vertical frequency response check (boxes with 100, 200 and 300
TV lines)
Horizontal and Diagonal frequency response check (boxes with 3.58 MHz
NTSC vertical bars, 300 TV lines vertical and diagonal, 400 TV lines vertical and diagonal, and 4.43 MHz
PAL vertical bars )