SFR results: MTF (Sharpness) plot

If you entered Imatest on this page, you may want to explore the background information in these links.
Sharpness introduces sharpness measurements and MTF.
Sharpening describes Standardized sharpening.
How to test Lenses with Imatest contains conscise instructions on testing lenses using SFRplus.
Image quality factors lists the factors measured by Imatest.

Imatest SFR displays Edge profiles and SFR (Spatial frequency response, i.e., MTF) plots with spatial frequency labelled in

• Cycles per Pixel (C/P),
• Cycles per distance (inches or mm),
• Line Widths or Pairs per Picture Height (LW/PH or LP/PH), and/or
• Cycles per angle (milliradians or degrees)

depending on the first two checkbox settings of the Plot section of the SFR input dialog box , shown below. Note that one cycle (or line pair) is equivalent to two line widths.

Key results below are shown in Bold. The most important is MTF50, without and with Standardized sharpening. Its relationship with print quality is discussed in Interpretation of MTF50. MTF curves and Image appearance contains several examples illustrating the correlation between MTF curves and perceived sharpness. The contents of the plots are affected by whether or not Standardized sharpening is checked in Settings section of the SFR input dialog box. Differences in plot content are indicated by [Std Sharpening checked] or [Std Sharpening off].

Edge response

Upper left: Spatial domain plot		Edge profile [Standardized sharpening on]
Black line (bold)	Edge profile for the luminance (Y) channel, where Y = 0.3*R + 0.59*G + 0.11*B. Original (without standardized sharpening). The normalized edge profile shown on the right is proportional to the light intensity. You may also select to display the Line Spread Function (LSF; the derivative of the edge profile), shown on the right, below, or Pixel levels (which includes gamma-encoding), or Edge linear unnormalized to view the unnormalized edges, which often gives a better idea of the degree of saturation that can affect results.
Red line (dashed, bold)	Edge profile for the luminance (Y) channel with standardized sharpening, indicated by (corr) for "corrected." Radius R used for setting standardized sharpening is displayed. Defaults to 2, but may set manually; may be larger for unusually broad transitions (poor MTF response).  [Std Sharpening checked]
R, G, B dashed lines (thin)	Individual edge profiles for R, G, and B channels. Shown more prominently in the Chromatic Aberration plot, below. Barely visible in this illustration because this camera has very little chromatic aberration. Imatest Master only.
Left column text (input settings)	Title, including measurement orientation. (A vertical edge is used for a horizontal profile.) Image height (H) or Width x Height (WxH) in pixels Total megapixels Channel. Defaults to Y (luminance). R, G, or B are also available. Gamma is an estimate of camera gamma used to linearize the image. Defaults to 0.5. Region of interest (ROI) size in pixels ROI location in percentage of distance from center to corner.
Right column text (results)	[not for LSF]  10-90% rise distance (original; uncorrected) in pixels and rises per picture height (PH). Line spread function [Std Sharpening off] [not for LSF]  10-90% rise distance (with standardized sharpening; indicated by (corr) for "corrected") in pixels and rises per PH. Radius R used for setting standardized sharpening is displayed. Defaults to 2, but may set manually; may be larger for unusually broad transitions (poor MTF response). Includes the equivalent "ideal megapixels" in brackets [...].  [Std Sharpening checked; not for LSF] [not for LSF; Imatest Master only]  10-90% rise distances of the R, G, and B channels, individually. Imatest Master only. [LSF only]  Peak LSF (maximum d(Edge)/dx) and PW50 (50% pulse width) in pixels (also called Full Width at Half-Maximum FWHM) and pulse widths per picture height (PH). RMS edge roughness in pixels. A promising measurement related to image quality. Shown on the right.  [Std Sharpening off] Overshoot and undershoot. Percentage of step amplitude. Shown if appropriate.  [Std Sharpening checked] Average pixel levels in dark and light areas, and light/dark ratio. Clipping can occur if they are too close to 0 or 255. Also gives the ratio between the light and dark areas: an indication of the contrast of the image.

Spatial Frequency Response (MTF)

Lower left: Frequency domain (MTF) plot
Black line (bold)	Spatial Frequency Response (MTF) for the luminance (Y) channel. Unprocessed. MTF curves and Image appearance contains several examples illustrating the correlation between MTF curves and perceived sharpness.
Red line (dashed,bold)	Spatial Frequency Response (MTF) for the luminance (Y) channel with Standardized sharpening.  [Std Sharpening checked]
Right column text (results)	MTF50 (50% contrast spatial frequency) for the original uncorrected image in cycles/pixel and line widths per picture height (LW/PH). Its relationship to print quality is discussed in Interpretation of MTF50. MTF50 (with standardized sharpening; corrected) in cycles/pixel and LW/PH. Radius R used for setting standardized sharpening is displayed. Defaults to 2 (larger for unusually broad transitions (poor MTF response)). It may be adjusted in the input dialog box. [Std Sharpening checked] MTF50P (spatial frequency where contrast is 50% of its peak value) for the original uncorrected image in cycles/pixel and line widths per picture height (LW/PH). This is the same as MTF50 for slightly to moderately sharpened edges, but smaller for oversharpened edges. It may be a better indicator than MTF50 of the perceived sharpness of oversharpened images. [Std Sharpening off] Oversharpening or undersharpening. The amount the camera is over- or undersharpened with respect to standardized sharpening. 100% ( MTF( feql ) - 1) where feql is the frequency where MTF is set to 1 by standardized sharpening.  [Std Sharpening checked] Secondary Readout  MTF20 (20% contrast spatial frequency for the original uncorrected image) and MTF @ 0.25 C/P are shown. (MTF30 is the default.) Up to two secondary readouts can be selected in the SFR input dialog window. You can select MTFxx, the spatial frequency for xx% contrast, or the MTF at a spatial frequency specified in cycles/pixel, pixels/mm, or pixels/inch. MTF at the Nyquist frequency. May indicate of the effectiveness of the anti-aliasing filter and likelihood of aliasing effects such as Moire patterns. But it not an unambiguous indicator because aliasing is related to sensor response, and MTF at Nyquist is the product of sensor response, the de-mosaicing algorithm, and sharpening, which can boost response at Nyquist for radii less than 1. Aliasing effects may become serious over 0.3. There is a tradeoff: the more effective the sensor anti-aliasing, the worse the sharpness. Foveon sensors (three colors per pixel) are more tolerant of aliasing than Bayer sensors, which are used in most digital cameras. Nyquist frequency: Half the sampling rate = 1/(2*pixel spacing). Always 0.5 cycles/pixel. Indicated by the vertical blue line.

Input data

Right: Input data
	Top right image Thumbnail of the entire image, showing the location of the selected region of interest (ROI) in red.
	Middle right image The selected region of interrest (ROI), shown with the correct aspect ratio, but not necessarily the exact size. The following parameters are displayed below the image. ROI size in pixels ROI boundary locations (Left, Right, Top, and Bottom) in pixels from the upper-left corner, Edge angle in degrees, and Estimated chart contrast, derived from the average pixel levels of the light and dark areas (away from the transition) and gamma. The equation:  Estimated chart contrast = (avg. pixel level of light area/avg. pixel level of dark area)^(1/gamma)
	Lower right text Selected EXIF data: metadata recorded by the digital camera. Only for JPEG files unless Phil Harvey's ExifTool (recommended) is installed. May include ISO speed, aperture, and other details. Thanks to Matthias Wandel for jhead.exe.