Modules

Rescharts

Rescharts— an interactive interface for sharpness measurements

Imatest™ Rescharts is a highly interactive interface for analyzing 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.

The following chart types are supported by Rescharts.

Slanted-edge SFR

 

SVG SFR chart, 3x5 grid
SVG SFR chart: m x n grid

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.

It supports all charts that contain slanted edge patterns, including the ISO 12233 chart and its derivatives. Charts may be purchased from the Imatest Store or created with Test Charts (SVG charts are especially recommended) and printed on a high quality inkjet (skill is required to do this well).

SFRplus

 

Highly automated analysis of SFR (MTF), Lateral Chromatic Aberration, distortion, and tonal response. 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.

SFRplus instructions

Log Frequency (simple)

 

 

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 Frequency instructions

Log F-Contrast  (not in Imatest Studio)

 

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.

Log F-Contrast instructions

Star chart   (not in Imatest Studio)

 

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.

Star Chart instructions

Wedge

 
Log F-contrast chart

Wedge pattern in ISO 12233 chart

Wedge  (Imatest Master only)

Analyzes hyperbolic or trapezoidal wedge patterns (converging bars with linear frequency or linear spacing) contained in the ISO 12233, EIA 1956, and other test charts, and included in the proposed revision to the ISO 12233 standard. Measures MTF (SFR) and the onset of aliasing (similar to the CIPA DC-003 standard).

Wedge instructions

Random Scale-Invariant

 
Log F-contrast chart
Random Scale-Invariant chart

Random (Scale-invariant)  (Imatest Master only)

Analyzes a random (scale-invariant) pattern, which has a 1/f fourier transform (1/f 2 Power Spectral Density (PSD)). Such a pattern has the same general appearance (the same statistics) regardless of distance. Since images of this pattern typically have little sharpening (due to the lack of contrasty edges) but relatively large amounts of noise reduction, it is an excellent indicator of a camera’s ability to render fine low-contrast detail. (Slanted-edges, by comparison, tend to be more sharpened and have less noise reduction, and hence may not give an accurate indication of a camera’s response to fine low-contrast detail.) Noise power measured in the smooth regions on the left, is subtracted from the PSD of the random pattern. Two low contrast slanted-edges are used to used to verify the random pattern results.

Random (Scale-invariant) instructions

Any Scene Sharpness

 
Log F-contrast chart
An example for Any scene sharpness

Any scene sharpness  (Imatest Master only)

Measures sharpness of any scene. The sharpness metric is nonstandard and applies to the individual scene only (it cannot be used for comparisons with other scenes). (It’s the same metric used in Find sharp files.) Useful for optimizing focus during reloads in the Image Sensor edition, which analyzes frames from live (video) feeds. Displays the image and a history showing changes in sharpness as the device is focused.

Any scene sharpness instructions (coming)

The Rescharts window

Detailed instructions for running Rescharts are found in Using Rescharts.

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.

IT8 a*b* display
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, which is described in detail in Using Rescharts..

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:

Edge and MTF (shown on the right)
Chromatic Aberration (right, below)
SQF (Subjective Quality Factor)
Noise spectrum & Shannon capacity
Histograms & noise stats (left, below)
Summary & EXIF (for JPEGs)

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 Edge and MTF display
SFR histogram
SFR Histogram
Lateral Chromatic Aberration
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.
Available displays:        Full instructions
Edge and MTF
Chromatic Aberration
SQF
Noise spectrum & Shannon capacity
Multi-ROI summary
Tonal response & gamma
Histograms and noise stats
Summary & EXIF (for JPEGs)

Rescharts SFRplus summary display
SFRplus summary display for 9 automatically-selected regions

Log Frequency (simple)

Log f pattern: valid for testing. Right-click to download
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..

Available displays:        Full instructions

The Pattern (original pixel levels and linearized)
MTF and Moire (linear frequency scale)
MTF and Moire (log frequency scale)
EXIF data

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 RedBlue 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.

Log frequency pattern analysis
Pattern (original pixel levels and linearized)

MTF and moire display
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.

Available displays:       Full instructions

The Pattern (original pixel levels and linearized)
MTF (linear frequency scale)
MTF (log frequency scale)
2D pseudocolor contour plots that can display any of several MTF-related parameters:

MTF (envelope – standard) (standard MTF, normalized to 1 at maximum contrast and zero spatial frequency)

Normalized contrast level (MTF normalized to 1 at zero spatial frequency for all contrast levels)

Normalized contrast loss (MTF normalized to 1 at zero spatial frequency for all contrast levels as well as all spatial frequencies at the maximum contrast level: shows contrast loss from ideal)

MTFnn or MTFnnP (spatial frequencies where MTF = nn% of the low frequency or peak value
EXIF data

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.

MTF and moire display
Normalized contrast level (MTF)
(1 at low frequencies
for all chart contrasts):
Panasonic TZ1, ISO 80

Log frequency-contast
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.

Available displays:       Full instructions

Display Description
MTF (original and linearized) MTF for up to 8 segments of the star. Both linear and logarithmic frequency displays are available.
MTFnn or MTFnnP Display MTFnn (the frequencies where MTF equals nn % of the low frequency values) and MTFnnP (the frequencies where MTF equals nn % of the peak value) for nn = 70, 50, 30, 20, and 10. Both polar (spider) and rectangular plots are available.
MTF contours (rectangular) Display MTF contours in a rectangular plot with linear or logarithmic frequency display. Similar to the MTFnn rectangular plot.
MTF contours (polar) Display MTF contours in a polar plot whose geometry duplicates that of the target.
EXIF data Show EXIF data if available.

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 Image settings & options.

MTFnn values from Log Frequency-Contrast
MTF contours, rectangular display,
Linear frequency scale.

 
MTF displayed in polar coordinates
MTF70 – MTF10: Polar coordinates,
Linear frequency on radius.