Imatest - Test Charts

Chart patterns

Charts are designed to fit on letter-size (8.5x11 inch), A4, A3, and Super A3/Super B (13x19 inch) paper, but they can be printed any size. A number of options, described below, are available for each chart. The first three patterns, SFR:quadrants, SFR rectangles, and Grid, are available in all versions. The remaining patterns are available in Imatest Master only.

SFR: quadrants (All versions)

This is the standard chart for SFR measurements. It should be tilted when it is photographed. Instructions are found in Using SFR, Part 1 and in How to test lenses with Imatest.

SFR: two rectangles (All versions)

This chart is also used for SFR measurements. It should be cut into two segments (left and right sides) and tilted in a manner similar to the SFR quadrants chart, above, when photographed.

Grid (All versions)

Grid generates test charts for the Distortion module.

Star chart (Imatest Master only)

Star charts can be used for observing performance (SFR, Moire patterns, and other image processing artifacts) at a variety of angles. In addition to the star (which has a selectable number of bands and either bar or sine form), the chart contains tonal calibration patches and slanted edges for checking results with SFR. Star charts will be analyzed in a future version of Imatest.

Log frequency-contrast gradient chart (1 and 2-band charts in Imatest Master only)

This chart displays bar or sine patterns of increasing spatial frequency. Several features resemble the Koren 2003 test chart described in Lens testing (pre-Imatest). This chart is valuable for viewing Moire fringing (colored bands caused by aliasing) and detail lost by software noise reduction, which takes place inside the camera and/or RAW converter, and which may remain even if you try to turn it off. Software noise reduction cannot distinguish noise from high spatial frequency low contrast detail, located in the lower right of the 1 and 2-band charts. The two and four band charts are designed to be printed on letter-size or A4 paper and cut into segments to be placed around the target, possibly in different orientations. The Log frequency-contrast chart will be analyzed in the Rescharts module, now under development .

	1-band chart
2 and 4-band charts

Each chart consists of the following patterns in 1, 2, or 4 bands. From top to bottom,

A bar of increasing spatial frequency (used to determine spatial frequency).
A sine or bar pattern of increasing spatial frequency (horizontally) and decreasing contrast (vertically) for 1 and 2-band charts. The contrast is proportional to the square of the distance from the bottom of this band. That emphasizes lower contrast areas, where noise reduction causes a loss of detail. It also corresponds to the way the eye sees, i.e., when the pattern contrast is one quarter of its maximum value, it appears to be about half the maximum. The contrast is constant for the 4-band chart, which is available in Imatest Studio.
(1-band chart only) 20 rectangular patches. 1 and 20 are black (0,0,0), 2 and 19 are middle gray, and 3-18 (16 patches) are a stepchart with density increment of 0.1 (if the chart is printed correctly, i.e., printer gamma mathes the Test Charts setting: some care is required).

Zone plate (Imatest Master only)

Zone plates (based on Fresnel diffraction) are useful for observing aliasing, particularly Moire patterns and other image processing artifacts. They have a much larger area with high spatial frequencies than the star chart. Thanks to Bart van der Wolf, who has done some interesting work with zone plates. In addition to the zone plate (which has a selectable number of bands and either bar or sine form), the chart contains tonal calibration patches and slanted edges for checking results with SFR.

Scalable Vector Graphics charts (SVG) (Imatest Master only)

Scalable Vector Graphics (SVG) images print at a printer's maximum quality regardless of size. They do not suffer from the pixellation that takes place when bitmap images are enlarged. The SVG chart shown on the right contains squares with slanted edges, "hyperbolic" wedges and bar patterns for viewing moiré caused by aliasing, and a step chart with density steps of 0.1 when the printer is in calibration. Five of these charts printed letter or A4 size and mounted at the center and corners of a 3x3 grid makes an excellent SFR test target, suitable for testing high quality DSLRs. Described here.

Several of the SVG charts consist of slanted squares arranaged on an m x n grid. A step chart (density increment = 0.1) and a pair of hyperbolic wedges may be optionally added. The chart's contrast, brightness, and several other details are adjustable. A typical SVG SFR chart, consisting of a 5x9 grid, is shown below. This chart is optimized to be printed large: on 24 inch widebody printers. It offers significant advantages over standard ISO 12233 charts: less wasted area, better suited to automated testing, larger ROI location tolerance, and better contrast control. These advantages are discussed here.

SVG SFR chart: 5x9 grid, 20:1 contrast, with optional hyperbolic wedge
and step patterns (0.1 density increment) .

Options

A number of options are available, including

Pixels per inch (PPI) for printing the chart. Affects the pixel size of the chart file.
Chart height (cm) . Choose from 18 cm (for A4), 20 cm (for US letter; 8.5x11 in.), 28 cm (for A3), or 30 cm (for Super A3/Super B; 13x19 in.). The chart can be printed any size. The number of vertical pixels is PPI * Chart height (cm) / 2.54.
Highlight color. In addition to the standard White/Black (or White/Gray) charts, you can replace white with any additive or subtractive primary color: R, G, B, C, M, or Y. Bayer sensors, used in most digital cameras, have half as many R and B sensors as G. Patterns with different highlight colors may perform differently in sharpness tests. A magenta star pattern is illustrated on the right.
Chart lightness. Affects the highlight color in charts with grayscale images (Star, Log-frequency, Zone plate). Lightest uses the least ink, but response may be smoother when one of the darker values is chosen.
Type (bar or sine). A bar star pattern is shown on the right; a sine star pattern is illustrated above.
Star pattern bands. Multiples of 4. The magenta pattern (on the right) has 36 bands); the above White-Black pattern above has 20 bands.
Contrast ratio. The ratio of the reflectivity of the light to dark areas (the upper zone only in the Log frequency chart). The maximum contrast ratio depends on the printer and paper. It is typically 100 or more for glossy (or luster) surfaces, but only around 60 for matte surfaces. Maximum print density = -log₁₀(minimum reflectivity) can be measured in Print Test. Reducing contrast ratio reduces clipping, which can be a problem in SFR measurements. The default value is 40 (the minimum recommended by the ISO standard), but 20 is recommended in most cases.
Gamma. You should use the value of gamma for your typical color space and workflow (2.2 is standard for Windows; 1.8 for older Mac systems). The default value of 2.0 is close enough to both for most purposes. Gamma affects the accuracy of grayscale patterns and the actual printed contrast ratio: it must be accurate to get the correct ratio.
Ink spread compensation corrects for ink spread (or "dot gain") in the Log frequency chart. Others may be added later.) The default is 0. The best value must be determined experimentally.

Test Charts

Creates test charts for high quality inkjet printers