Imatest - SFR results: Multiple ROI (Region of Interest) plot

Imatest SFR allows you to select several regions of interest (ROIs) in an image. Display options from the SFR input dialog box are shown below.

2D summary plot

When one of the 2D images (Cy/Pxl or LW/PH) are selected, the image below is displayed. It shows the regions of interest (ROI) and the following parameters for each ROI.

The dotted circles delimit the central region (up to 30% of the center-to-corner distance), the part-way region, and the corner region (over 75% of the center-to-corner distance). The New Weighted MTF50 is the weighted mean of the mean MTFs in the three areas, where the weights are 1 (Central), 0.75 (part-way), and 0.25 (corner).

Multi-ROI 2D summary plot, showing Center-corner distance,
MTF50, MTF20, and CA superimposed on image.

This display, introduced with Imatest 2.5.8 (January 2008), can be particularly useful because lenses are not always centered properly. If they were, performance would be a simple function of the distance from image center. You can quickly review the summary results, then look at the detailed results for individual regions. It was developed because about 9 regions (center, 4 - part-way out, 4 - corner) is sufficient to characterize lens performance, but not sufficient for a meaningful 2D or 3D contour plot (which requires about 20 regions). Also, contour plots can only show one parameter (e.g., MTF50), while this display shows several.

1D Summary plot showing results as a function of distance from the center

This figure contains two plots: MTF50 (upper left) and 10-90% rise distance (lower left). If Cycles/pixel is selected, units are relative to pixels; if LW/PH is selected, units are relative to image height. These figures show performance (MTF50 and rise distances without and with standardized sharpening). The Cycles/pixel Figure also plots Chromatic Aberration as a function of distance from the center of the image, scaled as the percentage of distance from center to corner (0 = center; 1 = corner).

The most important results below are shown in Bold. Illustrations are for the first figure (Cycles per pixel in this case).

Upper left: MTF50 (Half-contrast frequency)

This plot shows MTF50 (the half-contrast spatial frequency) as a function of distance from the center of the image, scaled as the percentage from center to corner (0 = center; 100 = corner). There are two vertical (y) axes. The primary axis is on the left; the secondary axis (italicized) is on the right. These alternate for the two plots. In this plot, the primary axis is in Cycles/pixel for MTF50 and Pixels for 10-90% rise distance. It can also be in Cycles/mm or Cycles/inch if specified in the SFR data window.

Black line (bold)

MTF50 (half-contrast spatial frequency) for the luminance (Y) channel. Unprocessed. This is the number to use for measuring lens sharpness.

Red line
(bold, dashed)

MTF50 for the luminance (Y) channel with Standardized sharpening. This is the number to use when making general comparisons of different cameras with different degrees of sharpening.

Symbols and numbers
below data points,
top to bottom

Orientation: Location of region relative to image center. A = Above, B = Below, L = Left, R = Right.

MTF50, Uncorrected and with Standardized sharpening, in units corresponding to the primary vertical (y) axis scale on the left. The vertical order is determined by the order of the data points, i.e., if the Uncorrected MTF50 is higher, its value is on top.

MTF50, Uncorrected and with Standardized sharpening, in units corresponding to the secondary vertical (y) axis scale on the right. These numbers are italicized. The vertical order is determined by the order of the data points, i.e., if the Uncorrected MTF50 is higher, its value is on top.

Right column: Crop, Results summary, and EXIF data

Top right image
Thumbnail of the entire image, showing the locations of the selected regions of interest (ROI) in red.

Middle right box:
Weighted MTF50
Results summary

Summary of key results of multiple ROI runs:

Weighted mean values for MTF50, in cycles per ... and LW/PH units, without and with standardized sharpening. The MTF value at the middle of each (sorted) line segment is weighted according to the length of the line segment and the distance from the center: the center is weighted twice as strongly as the corner. These weights are used to calculate a weighted mean. This algorithm prevents closely spaced points from being given excessive weight.

Lower right text
Selected EXIF data: Data recorded by the digital camera. Only for JPEG files. May include ISO speed, aperture, and other details. Thanks to Matthias Wandel for jhead.exe.

Lower left: 10-90% Edge rise distance		The Legend at the lower right of the 10-90% Rise distance plot sometimes covers data points. It can be moved by clicking and dragging it with a mouse.
Black line (bold)	The 10-90% rise distance, uncorrected (without Standardized sharpening).
Red line (bold, dashed)	The 10-90% rise distance, with Standardized sharpening.
.Blue line (bold, dashed) with yellow circles.	Chromatic aberration (Area-based) in pixels. An indicator of the severity of CA. The area between the channels with the highest and lowest levels. In units of pixels because the x-axis is in pixels and the y-axis is normalized to 1. Explained in detail in the page on Chromatic aberration. Meaning: Under 0.5; insignificant. 0.5-1: minor; 1-1.5: moderate; 1.5 and over: serious.

When the SQF (multi) checkbox in the SFR input dialog box has been checked, a multiple ROI SQF Figure is produced.

The upper plot shows SQF without standardized sharpening (unprocessed) for picture heights from 10 to 60 cm. The lower plot shows SQF with standardized sharpening (R = 2). Weighted SQFs are shown in the table on the right. The weighting formula is the same as the one used for MTF: readings near the center are given twice the weight of readings near the edge.

Geometry & file shows the Regions of interest (ROIs) in pixels and the CSV summary files for each location.

nroi – roi_mult These four lines are used to define the regions in imatest.ini. These regions can be reused for Imatest runs by copying and pasting the four lines into imatest.ini, replacing the previous lines. Imatest.ini can be opened for editing by clicking Settings (in the Imatest main window), View settings (ini file).

Summary results The table contains summary results. These results are repeated in a single-column at the end of the CSV file, shown below. Though it is less readable, it is much better suited for copying and pasting summary results into an Excel file that can be used to produce plots.

Explanation of summary results Each of the results are presented six times— for different regions of the image and for a weighted sum of the regions, as described below.

The column in this table (rows in the single-column table below) contain the following results:

Secondary results These include results with standardized sharpening (suffix C).

Creating Excel plots

The single column summary is the last table in the multi-ROI CSV file. It contains the same data as the summary results (above), but it is formatted so it can be easily copied and pasted into another Excel file for creating plots that summarize several runs. For mult-ROI batch runs, this data is combined into a CSV output file with a name of the form, filename_Y_sfrbatch.csv.

Summary plot for 6 multi-ROI runs (f/5.6-f/32) for the Canon 17-85mm IS lens on the EOS-40D (JPEG)
The Excel file was created by combining single-column summary results from the 6 runs.