Introduction
Imatest™ Rescharts analyzes images of several test charts for resolution-related parameters such as sharpness (i.e., spatial frequency response; MTF), color moiré, and fine detail lost to software noise reduction, using a highly interactive user interface is similar to Multicharts.
The following chart types are supported by Rescharts.
Duplicates SFR, but with a far more interactive interface. It calculates and displays the average edge, SFR (Spatial Frequency Response or MTF), and Lateral Chromatic Aberration. Includes one figure not in SFR: a histogram with noise analysis.
It supports all charts that contain slanted edge patterns, including the ISO 12233 chart and its derivatives. Charts may be purchased from sources such as Applied Image or created with Test Charts (SVG charts are especially recommended) and printed on a high quality inkjet.
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Highly automated analysis of SFR (MTF), Lateral Chromatic Aberration, distortion, and tonal response. Introduced in Imatest 3.2. Uses a special test chart, shown on the left. Unlike other Rescharts modules, SFRplus does not require manual region (ROI) selection: it is performed automatically. Running SFRplus in Rescharts saves settings for fully automated runs. |
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Analyzes a sine or bar pattern of increasing spatial frequency. Measures SFR more directly, but less precisely, than the slanted-edge method. Also measures color moiré (Imatest Master only), which is a function of lens sharpness, anti-aliasing filter, and demosaicing algorithm. Spatial frequencies are detected automatically. Charts can be created by Test Charts and printed on a high quality inkjet printer. Also works with the old test chart in Lens testing. |
Log F-Contrast (Imatest Master only) Analyzes a sine or bar pattern of increasing spatial frequency on the one axis and decreasing contrast on the other. Measures SFR for a range of contrast levels. Useful for measuring the loss of fine detail caused by software noise reduction— the effects of nonlinear signal processing. The chart can be created by Test Charts and printed on a high quality inkjet printer. |
Star chart (Imatest Master only) Analyzes a sinusoidally-modulated Siemens star chart (144, 72, or 48 cycles); proposed for the revised ISO 12233 standard. Measures MTF (SFR) for 8, 12, or 24 segments around the circle. Has a large variety of displays. The chart can be purchased from Image Engineering or created by Test Charts and printed on a high quality inkjet printer. |
Getting started
Instructions for purchasing or creating test charts can be found on pages for individual tests: SFR, Log Frequency, and Log F-Contrast.
Photograph or scan the chart, taking care to avoid glare, which can be problematic in charts with semigloss and glossy surfaces. Glare can be especially difficult to control with wide angle lenses. A recommended lighting setup is described here and in How to build a testing lab.
To start Rescharts, run Imatest, then click the button. The Rescharts window will appear with brief instructions, which may be more up-to-date than the ones shown below.
Select an image to analyze by
The button and Chart type popup menu are highlighted (yellow background) when Rescharts starts. |
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A standard Windows dialog appears with the chart type indicated in the title. Open the image file. Multiple files can be opened for averaging (but batch (sequential) runs are not supported by Rescharts).
For all modules other than SFRplus, if the image is the same size and type as the previous image analyzed by Rescharts, you'll be asked if you want to use the same ROI (region of interest). (ROI selection is entirely automatic with SFRplus.)
If the image size or type is different or if you answer No, a coarse cropping box appears. The initial crop doesn't have to be precise: you'll have a chance to refine it.
- For Slanted-Edge SFR, select the region you want. Recommended cropping.
- For Log Frequency (simple), select a narrow strip running from along the direction of increasing spatial frequency. Narrow strips of the Log Frequency-Contrast chart can be used.
- For Log F-Contrast, select most of the chart image, leaving small margins (1/2 to 1% of the image dimensions) at the edges.
After the rough crop has been selected, the fine adjustment box appears, showing the coarse crop as a rectangle. This dialog box can be enlarged or maximized to facilitate the adjustment. It offers numerous options.
Crop for the Log Frequency-contrast chart. Leave a small margin
(1/2 - 1% of the image height) at the top and bottom.
- The entire ROI can be moved ( , upper-left).
- The top, bottom, left, or right sides can be moved ( , middle-left).
- You can choose between Fine, Coarse, and Extra Coarse movement (1, 5, or 25 pixels of movement per click).
- The display can be zoomed out or in.
- Pixel values for the four corners can be entered (X(tl), Y(br), ..., where tl = top-left, br = bottom right, etc.). The origin is the upper-left. Be sure to press the Enter key after entering a value.
When you have completed the fine adjustment, click one of the buttons on the bottom of the window. If you click , an additional dialog box may appear. The entries in this dialog box can be changed later by clicking on in the Rescharts window. If you click , it will go directly to the Rescharts window, using saved (recent) values.
The Rescharts window
After the image file has been entered, calculations are performed and the most recent Chart view is displayed. The MTF/contrast (2D pseudocolor contour) display (actual MTF when a sine chart is used) for Log F-Contrast is shown below.
MTF contours for Canon EOS-20D, 24-70mm f/2.8L, 42mm, f/5.6, ISO 100
The main display image is on the upper left. Additional text results may appear below this image. An image of the chart is shown on the upper right. You can choose to display the whole image or the crop (ROI). The remainder of the right side is the control area.
The checkbox turns Zoom on and off.
The buttons to the right of set the display to either the or a of the image (the selected ROI).
Image and Display areas
The image area is on the right of the Rescharts window, just below the and buttons. It includes the the button, the Chart type dropdown menu (described above), and additional controls.
Immediately below the Chart type menu is the New crop (same image) menu, which has identical entries. If an item is selected on this menu, the image is recropped for analysis by the selected chart type (which may be the same or different). This menu is useful when several regions of an image need to be analyzed or when the target contains more than one chart type. brings up the input dialog box for the selected chart type. This is the same box that appears when you press (not Express mode) in the ROI repeat or ROI selection window. Display, immediately below the image area, selects the results to display. Choices depend on the chart type. |
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The Display options area is immediately below Display. The contents, which depend on the Display selection, are described below in the sections for the individual displays.
(shown on the right) saves a snapshot of the current display (the entire Rescharts screen) as a PNG file (a widely-used losslessly-compressed format). It also allows you to immediately view the snapshot (if the Open window... box is checked) so it can be used a reference for comparing with other results. File name and Directory at the top of the window set the location of the file to save. When you check the Open window in an image viewer... box, the current screen will be opened either the system default viewer (if the box under Image viewer is blank) or a viewer/editor of your choice (if the box contains the path name to the viewer/editor). I recommend Irfanview, which is fast, compact, free, and supports an amazing number of image file formats. (It can be valuable for converting nonstandard images to Imatest-readable formats.) Its normal location in English language installations is C:\Program Files\IrfanView\i_view32.exe. |
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Saves detailed results in CSV and XML formats. The exact content depends on the module.
opens this web page in an HTML browser window.
terminates Imatest Rescharts, but the Imatest main window remains available.
Rescharts modules
This section describes the Rescharts modules, illustrating some of the available displays and options. More information is available in the pages for the individual modules (Chart type analyses).
Slanted-edge SFR
Slanted-edge SFR measures sharpness as Spatial Frequency Response, also called MTF (Modulation Transfer Function) from images of slanted edges, as described in Sharpness. ROI (Region of Interest) selection, calculations, and output largely duplicate SFR. Available displays:
The principal differences from SFR are the highly interactive interface and an added histogram of the ROI levels, shown below. Black is the entire ROI. Cyan is the portion on the left and red is the portion on the right, both away from the edge. The upper histogram is for the original image (pixel levels/255); the lower histogram is for the linearized image (gamma applied). |
 SFR Edge and MTF display |
 SFR Histogram |
 SFR Lateral Chromatic Aberration |
SFRplus
| SFRplus, introduced in Imatest 3.2, performs a highly automated analysis of SFR (MTF), lateral chromatic aberration, distortion, and tonal response, using a special test chart. Unlike other Rescharts modules, SFRplus does not require manual region (ROI) selection: it is performed automatically. Running SFRplus in Rescharts saves settings for fully automated runs. |
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SFRplus summary display for 9 automatically-selected regions
Log Frequency (simple)
Log frequency image: right-click to download an image that can be used for testing.
Log Frequency measures image contrast of charts that increase in spatial frequency on a logarithmic scale (log frequency increases with x). When the image pattern is sinusoidal (not a bar pattern) the contrast is equivalent to SFR or MTF. This method is more direct than Slanted-edge SFR, but less accurate because it is degraded by noise and sampling phase variation. It also measures color moiré (Imatest Master only). The chart can be created by Test Charts and printed on a high quality inkjet. Also works with the test chart in Lens testing and narrow strips of the Log Frequency-Contrast chart..
The display on the right shows Contrast (MTF) on the top and color moire on the bottom as a function of spatial frequency (displayed linearly). Color moire can me measured in several ways: R-B (normalized Red − Blue channel) is shown on the right. The total color moire is the spread of values above 0.3 cycles/pixels (indicated by the red curve). Details of the color moire measurement can be found in Log Frequency. The Correct for color density box should be checked for best results.
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 Log Frequency MTF and moire display (linear x-axis frequency scale) |
Log F-Contrast
Log F-Contrast (short for Log Frequency-Contrast) measures the image contrast of charts that vary in spatial frequency on one axis (log frequency increases with x) and in contrast on the other (contrast is proportional to ( y/h)2 for image height h). When the image pattern is sinusoidal (rather than a bar pattern) the contrast is equivalent to SFR or MTF. This module can be used to measure how much fine, low-contrast detail is lost to software noise reduction. The chart can be created by Test Charts and printed on a high quality inkjet printer.
The displays on the right show the Normalized contrast level (MTF normalized to 1 at low spatial frequencies for all chart contrast levels) for the Panasonic TZ1 camera with ISO speed set at 80 (top) and 800 (bottom). Spatial frequency is on a linear scale with a maximum displayed frequency of 0.5 cycles/pixel. The difference between the two images is quite striking. The TZ1 has much more noise reduction— and correspondingly less detail— at ISO 800. These plots are explained in detail in Log F-contrast. |
 Normalized contrast level (MTF) (1 at low frequencies for all chart contrasts): Panasonic TZ1, ISO 80  Normalized contrast level: TZ1, ISO 800 |
Star chart
Star Chart measures contrast (MTF or SFR) of sinusoidally-modulated star charts (also known as the Siemens star) proposed for inclusion in the updated ISO 12233 standard. Charts have 144, 72, or 48 cycles and can be analyzed in 8, 12, or 24 segments. Star charts can be purchased from Image Engineering or created by Test Charts and printed on a high quality inkjet printer.
The displays on the right show MTF contours and MTF70 through MTF10 (spatial frequencies where MTF = 70 through 10% of the low frequency level). Spatial frequency is displayed in cycles per pixel, but Line Widths per Picture Height (LW/PH), cycles/inch, or cycles/mm can be selected by pressing . |
 MTF contours, rectangular display, Linear frequency scale.  MTF70 – MTF10: Polar coordinates, Linear frequency on radius. |
