Test Charts creates test chart files for printing on high quality inkjet printers. This page focuses on Scalable Vector Graphics (SVG) charts for measuring sharpness (MTF) with Imatest SFR and SFRplus. (Bitmap charts are described elsewhere.) SVG charts can be printed any size at a printer's maximum quality (i.e., resolution) with no limitations, and they generally require much less storage than bitmap images. Several of the SVG charts are well suited for automated testing with SFRplus and have numerous advantages over the widely-used ISO 12233 chart.

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Vector graphic images consist of primitives such as lines, polygons, etc., that can be scaled to any size and do not suffer from the pixellation problems of bitmap images. They print at the printer's maximum quality, regardless of size. Vector graphics are excellent for generating test charts consisting of lines, curves, and areas that don't require complex tone variations such as sine modulation.

Scalable Vector Graphics (SVG) is an XML file format recognized by the World Wide Web Consortium (W3C). SVG files can be read, edited, and printed by Inkscape— an excellent free open-source program (described in Wikipedia). They can also be imported into Adobe Illustrator, Corel Draw, and others. SVG implementations are listed here.

Imatest can create SVG files consisting of lines and polygons, but unfortunately not circles or Bezier curves. This is sufficient for making outstanding targets for measuring SFR and aliasing (moiré patterns, usually colored). Contrast, lightness, and highlight color are selectable.

Introduction: SVG chart designs and advantages

Slanted squares on m x n grids

Most of the SVG charts consist of slanted squares arranged on an m x n grid. A step chart (density increment = 0.1) and a pair of hyperbolic wedges may be optionally added to some of the charts. The chart's contrast, brightness, and several other details are adjustable. The standard SVG chart for SFRplus, consisting of a 5x9 grid, a 4x5 stepchart, and bars at the top and bottom, is shown below.

SVG SFR chart: 5x9 grid
SFRplus chart: 5x9 grid, 10:1 and 2:1 contrasts, with step pattern (0.1 density increment)
and focus star. Designed for the automated SFRplus module.

This chart is is designed to be printed large (at least a 24-inch widebody photographic printer is recommended) and used with the SFRplus module that features automatic ROI (Region of Interest) selection. In addition to MTF, it's useful for measuring lateral chromatic aberration, lens distortion, gamma (contrast), and tonal response. It should not be printed small (letter-size or A4) on inkjet printers because SFR test results may be limited by the printer's resolution. Other grid patterns are available that are optimized for printing at different sizes. Grid choices include 1x2, 2x3, 3x5, 4x7, 5x7, 5x9, and 7x11. (4x7 and larger work with SFRplus.) The smaller grids (1x2 and 2x3) are designed to be printed relatively small (up to 13x19 inches) with several mounted on large foam boards (32x40 inches or larger) for analysis with SFR. The larger grids (3x5 and up) are optimized for printing on wide format printers, and are available in Imatest Master only.

ISO 12233 chart
ISO 12233 chart.

The squares are tilted as shown to facilitate the measurement of Lateral Chromatic Aberration, which is done best using tangential (or near-tangential) edges near the boundaries of the image.

SFRplus charts have a number of significant advantages over the standard ISO 12233 chart, shown on the right.

ISO chart selection tolerance
ISO chart ROI selection:
Low (vertical) position tolerance.
SVG chart selection tolerance
SVG chart ROI selection:
High position tolerance.

SVG pattern, 4x7 grid, dual contrast, inverted
SVG SFR chart: 4 x7 grid, inverted tones, 20:1 primary (2:1 secondary) contrast,
with optional step pattern (0.1 density increment; this version not compatible with SFRplus).

Imatest can supply custom SVG test charts in a variety of sizes. Contact sales at imatest dot com for details.

SVG Squares & Wedges (for printing letter size, A4, etc.)

Small SVG chart; 3x3 arrangement
3x3 chart arrangement (for letter/A4 prints)

This pattern consists of tilted squares, "hyperbolic" wedges, bars of varying spatial frequencies, and a replica of the Kodak Q-13 step chart with density steps of 0.1. It is optimized for printing A4 or letter size on a high quality inkjet printer and mounted on a 3x3 grid, as shown on the right— though it can be printed any size without loss of quality. This arrangement it will have a field width of around 32 inches (80 cm), sufficient for measuring the performance of the best modern DSLRs.

If you require a chart printed on a single sheet or if you plan to do automated testing, one of the m x n slanted square on grid charts described above (preferably 5x9) is recommended.

The chart below was created using Contrast ratio = 20, Gamma = 2.2, Highlight color = White, and Chart lightness = Light. The highlight and dark pixel values are 243 and 62, respectively, resulting in a display contrast of (243/62)2.2 = 20.2 at display gamma = 2.2. One or two of the corner charts could have very low contrast (2 or lower) to better characterize cameras with nonlinear signal processing.

A contrast ratio of 20 is high enough to turn on the maximum sharpening in cameras with nonlinear signal processing (which sharpen only in the presence of edges), but not so high that it is likely to cause clipping (pixel levels 0 or 255). It is half the minimum value of 40 in the soon-to-be-replaced ISO 12233 standard, now understood to be too high for reliable results. We also recommend printing a low contrast target— with contrast = 2 or lower— to better characterize camera performance. Results at contrasts = 20 and 2 will differ— often strongly— in the presence of nonlinear signal processing, which is nearly universal in consumer digital cameras.

Small pattern
SVG Squares and Wedges pattern

Chart details: The edges in the center square and the solid on the lower right are tilted approximately 5.7 degrees (arctan(0.1) ) for use in SFR. The converging line patterns ("hyperbolic" wedges) are intended for viewing moiré patterns: colors resulting from aliasing near the Nyquist frequency. They can be analyzed with the Wedge module, which measures MTF and vanishing resolution (the onset of aliasing) using techniques based on the CIPA DC-003 standard . The high frequency pattern goes from 400 to 2000 line widths/box height (LW/BH), where "box height" is the distance from the top to bottom of the active chart area (the rectangle just inside the outer rectangle, which represents the entire page). The low frequency pattern goes from 50 to 500 LW/BH. To convert to line widths per picture height (LW/PH), multiply LW/BH by the vertical pixel count and divide by the number of vertical pixels in the box. Some scale marks are omitted because of chart crowding.

The bar patterns on the left and right vary in spatial frequency from about 50 to 2000 LW/BH. They are uncalibrated. The step chart pattern on the right has density steps of 0.1 if the image is printed correctly: it is a replica of the Kodak Q-13 chart. If the printout is correctly calibrated, i.e., if the printer actually prints with the specified gamma, a Kodak Q-13 chart placed adjacent to the pattern will have identical tones (by visual inspection or scanner image readout). In this case, the printed chart contrast (10 in the above example) will be as specified.

Two charts are available for download. Each is 304 KB (SVG) or 500 KB (PDF— for those of you who don't want to bother installing Inkscape). Right-click on the links to save the file.

The high contrast (20:1) chart may be too contrasty for some cameras— highlights and/or shadows may clip. Chart contrast can be edited by opening the chart in Inkscape and selecting the white area of the image. A message at the bottom of the window will say something like, "Group of 5 objects in root." Rght-click, select Ungroup, click outside the object, then click inside the white area again. Now the message at the bottom will say something like, "Group of 548 objects in root." Again, right-click, select Ungroup, click outside the object, then click inside the white area. This time the message at the bottom should say, "Group of 1 object." Click on Object, Fill and Stroke... Select the Fill tab and click on the Flat color box (to the right of X). Click on the HSL tab. The original value of L should be 243 for this chart (it may not display). Set L for a a lower value. Around 200-220 should work well, even for very contrasty cameras. The final contrast for charts printed at gamma = 2 2 is (L/62)2.2.

USAF 1951 resolution chart

USAF 1951 resolution chart
USAF 1951 resolution chart

 

The venerable USAF resolution 1951 chart has been added in Imatest 3.6 because we plan to use it in Rescharts Slanted-edge SFR and SFRplus as an example of how MTF affects the appearance of standard images. We do not recommend printing this chart and/or using it for testing. It is poorly suited for automated measurements (much space is wasted), but for better or worse, it's familiar and makes a good visual example. Numeric annotations (mostly useless) are omitted.

Adjacent bar pattern sizes differ in size by a factor of the sixth root of two (21/6 ). The chart is described on http://en.wikipedia.org/wiki/1951_USAF_resolution_test_chart.

Operation

To run Test Charts, run Imatest and click on Test Charts in the Imatest main window. The following dialog box, shown for a 5x9 SVG grid pattern, appears. The available settings change for different patterns. Pattern selections for the SVG charts are shown in boldface on the left.


Test Charts input dialog box for SVG patterns

Pattern selections
SFR: quadrants
SFR: 2 rectangles
Grid
Star
Log frequency-contrast
Zone plate

SVG Squares & Wedges (letter, A4...)
SVG Squares 1x2 (letter, A4...)
SVG Squares 2x3 (>=A3)
SVG Squares 3x5 (>=Super A3/B)
SVG Squares 4x7 (>=Super A3/B)
SVG Squares 5x7 (>= 50 cm (20") h)
SVG Squares 5x9 (>= 50 cm (20") h)
SVG Squares 7x11 (>= 60 cm (24") h)
SVG Squares 2x3 (Same orientation)

Select the Pattern (the type of chart), the options, and the folder (directory) and file name for the test chart file. When you are ready to create the file, click on Create test chart. You may cancel by clicking on Close. When the calculations are complete a figure showing the chart (not for printing) appears. You can zoom in to see the fine detail.

The figure with the image of the chart is for preview only: it shows you what the chart looks like and lets you zoom in if you want. Do not print the chart directly from this figure. To print SVG charts, load the Print Test SVG output file (chart_temp.svg in the above example) into an editor that supports SVG. (Inkscape is recommended; Adobe Illustrator, Corel Draw, and others can also be used.) This will allow you to select the size of the print, add annotations, use color management, etc.

Options

Pattern

SVG Squares and Wedges

Two types of SVG pattern are available: Squares and Wedges (shown on the right; described above), and squares on a grid (1x2, 2x3, 3x5, 4x7, 5x9,  or 7x11; described above). The Squares and Wedges pattern and the 1x2 patterns are designed to be printed small (letter-sized or A4) and mounted in a grid arrangement (typically 3x3) to be photographed. The other grid patterns (3x5 and larger) are designed to be printed larger. The 5x9 and 7 x11 charts are particularly well suited for large format (24 inch and greater) printing. The 2x3 (same orientation) chart is designed to be printed up to Super A3/B (13x19 inches) and placed near the corners of a large target (typically 40x60 inches; 1x1.5 meters). This requires that two of the charts be printed as mirror images, which can be obtained in Inkscape by selecting the chart then clicking on Object, Flip Horizontal.

Highlight color

Magenta 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.

Different colors are of particular interest in analyzing Bayer sensors, where alternate rows of pixels are sensitive to {R, G, R, B, R, ...} and {G, B, G, B, G, ...}. Since there are only half as many R and B sensors as green sensors (and one quarter as many as total pixels), one would expect MTF to be poorer for red-black and blue-black charts than for white-black). Demosaicing algorithms typically make use of different colored pixels for calculating detail (i.e., an edge in the red channel would be sharper if information is present in the other channels). Also, different algorithms perform differently.

Contrast ratio

Choices: None, Maximum, 80, 50, 40, 25, 20, 10, 5, 4, 2, 1.414, 1.2, 1.1

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 around 100 for glossy (or luster) surfaces, but only around 40 for matte surfaces. Maximum print density = -log10(minimum reflectivity) can be measured in Print Test or estimated by Gamutvision. Available selections are Maximum and 80 through 1.1.

Clipping is often a problem with high contrast targets. The ISO-12233 standard calls for a contrast ratio between 40 and 80, but recent experiments have shown that lower contrast ratios produce more accurate and consistent results, which are less affected by gamma and camera nonlinearities. In 2007 the ISO standard will change to recommend lower contrast chart. The default value for Test Chart is 40 (the minimum recommended in the ISO standard), but 20 is preferred in many cases.

Contrast ratio affects MTF (SFR) measurements in cameras that perform nonlinear signal processing, i.e., noise reduction and sharpening with thresholds— nearly universal in consumer cameras. Charts with at least two contrast ratios: 20 and 2 (or lower) are recommended for characterizing cameras. This is handles with Contrast (alt) (below).

Contrast (alt)

Choices: None, Maximum, 80, 50, 40, 25, 20, 10, 5, 4, 2, 1.414, 1.2, 1.1

Selects a second contrast ratio to display in a few regions in the lower left quadrant — Contrast (alt) = 2.0 is used in four regions in the 5x9 chart shown in the preview images above and below. Available selections are None, Maximum, and 80 through 1.1. All squares in the chart have the same contrast if None is selected. Contrast (alt) is of interest because the nonlinear signal processing in many (perhaps most) digital cameras causes high contrast edges to be sharpened much more strongly than low contrast edges so that high and low contrast edges have different MTF measurements.

Gamma

Choices: 2.5, 2.2, 2.0, 1.8, 1.5, 1.0

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 is 2.2. Gamma affects the accuracy of the printed contrast ratio and the optional step chart: it must be the same value used for printing (the value of the color space, i.e., 2.2 for Adobe RGB (1998), if color management is used) to get the correct contrast ratio. Note that this is printer gamma, which is only indirectly related to camera gamma, which can be measured with Stepchart using the optional grayscale Step chart.

Added graphics

Affects the slanted square on m x n grid patterns.
None:  No added graphics. The chart is a pure grid of squares.
Stepcharts:  Stepcharts (density step = 0.1) are added to all m x n grid patterns except 2x3.

All:  Add Stepcharts, and add a pair of hyperbolic wedge patterns (converging lines) to the 5x9 and 7x11 patterns.
All (small step ch):  Add small Stepcharts and hyperbolic wedges to the 5x9 and 7x11 patterns.

Chart lightness

Choices: Lightest, Light, Mid-light, Middle, Mid-dark, Darkest

Determines the grayscale level of both the light and dark areas of the chart. Valuable for SFR edge charts, where middle tones are likely to be in the camera's linear response region.

Hexagon chart

Invert light/dark, hexagons

Choices: Normal, Invert, Normal (Hexagons), Invert (Hexagons)

Invert light and dark in all regions of the chart except for the Step chart (grayscale). Illustrated above.

If (Hexagons) is specified, replace squares with hexagons. Hexagons have near-45 degree edges in addition to near vertical and near-horizontal edges, which makes them useful for examining motion-related blur. Hexagon orientation alternates. Illustrated on the right.

Lightness (alt)

Choices: Lightest, Light, Mid-light, Middle, Mid-dark, Darkest

Lightness of the regions with the second (alternate) contrast ratio.

Output figure

The output figure contains a preview image of the test chart. It is not anti-aliased. This figure is not intended for printing. To obtain a printout of the chart, open the SVG image file in an editor such as Inkscape, following the instructions below. A high quality inkjet printer is recommended.


SVG chart preview (not for printing; use the output file!; not compatible with SFRplus)

You can zoom in on the chart by selecting an area or clicking on a point of interest. Double-clicking restores the complete image.

SVG chart preview zoomed
The preview looks jagged because the preview image lacks anti-aliasing.

The SFRplus chart

Although we recommed purchasing the SFRplus chart from the Imatest Store, you can print it yourself if you have a widebody photographic-quality inkjet printer and some skill (i.e., knowledge of color management). The Test Charts window for creating the standard SFRplus test chart is shown below. Several options, most importantly different grids (4x7, 5x7, 5x9, and 7x11) and square contrasts, are compatible with SFRplus. These options are listed below.

Test Charts settings for SFRplus
Test Charts window, showing settings for the standard SFRplus chart.
Additional settings are listed below.

Valid options. The standard values are enclosed in brackets [...].

Specify the folder and file names in the boxes on the lower right, then click Create test chart to save the chart in SVG format.

Print the chart following Instructions in below. Prints should be made with photographic quality inkjet printers on high quality paper: semigloss, luster, or smooth coated matte. Print (paper) size can be as small as13x19 inches for low resolution images (under 3 megapixels), but chart width should be at least 24 inches for compact digital cameras) and 38 inches (which fits nicely on 40 inch foam board) for DSLRs and other cameras with 10+ megapixels. Be sure the edges look clean and sharp to your eyes; examine them with a good magnifier or loupe. Chart quality is described in detail in Chart quality and distance.

If you choose to print the chart we strongly recommend that you be familiar with high quality color-managed photographic printing. You'll need a widebody photographic-quality inkjet printer. Instructions are complex and should be followed with care. NEVER print charts on plain bond paper. Edge quality is poor and test results tend to be more indicative of (poor) chart quality than the system under test.

The printed chart should be mounted on 32x40 or 40 x60 inch sheets of 1/2 inch (12.5 cm) thick foam board with spray adhesive or double-sided tape. 1/2 inch foam board stays flatter than standard 1/4 or 3/8 inch board.

Printing SVG charts

Depending on the version you may be able to print SVG charts directly from Inkscape. We've had success with Inkscape 0.45 but trouble with 0.46. The jury is still out on 0.47. A reader has reported success in printing from Adobe SVG Viewer, which will not be supported after January 1, 2009. Images can also be

You should always preview printed images prior to issuing the final print command.

Printing from Inkscape

Document Properties window
Document Properties window

 

Click File, Document Properties... to open the Document Properties window, shown on the right. Display the Page tab. Under Format you can select a standard page size such as US Letter, A4, etc., or you can select a custom page size. Surprisingly, most large inkjet printers require custom page size. For example, for a 13x19 inch print, enter 19.00 for Width, 13.00 for Height, and in (inches) in the units box to the right of Width. Page orientation: should be set to Landscape. When you have finished selecting the page size, click X on the upper-right to close the window.

 

In the Inkscape window (below), select the figure, click on the small padlock icon between W and H to lock the aspect ratio, then set either W or H to the desired dimension. The other will follow. Set X to the left and Y to the bottom margins. The values shown (X = 0.5, Y = 0.25, W = 10, H = 8, in (inches)) center the image on US Letter-size 8.5x11 inch paper. Alternatively, you can enlarge the image by dragging one of the corner arrows while pressing the Ctrl key to maintain the aspect ratio.


Inkscape window
Portion of Inkscape window showing print settings (X, Y, W, H,...)

Epson R2400 Print dialog box
Epson R2400 printer driver dialog box

Adobe RGB (1998) is the recommended input profile because it has a gamma of exactly 2.2 (sRGB is only approximately 2.2). Relative Colorimetric rendering intent should have a more linear response than Perceptual (see Black Point Compensation). Print Preview should be checked because the print size will only be correct unless all settings described above are exactly correct-- Inkscape is quite unforgiving with print size settings. The preview can be rather slow.

Inkscape Export Bitmap window
Inkscape Export Bitmap dialog box

Printing a bitmap file from an image editor

Very large charts may require huge file sizes with this approach. We recommend printing directly from SVG or PDF files.

Printing a PDF file from Foxit reader

Foxit Reader print dialog
Foxit Reader print dialog box




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