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Measure spatial frequency response using Imatest^{®}
eSFR chart

`sharpnessTable = measureSharpness(chart)`

`sharpnessTable = measureSharpness(chart,Name,Value)`

`[sharpnessTable,aggregateSharpnessTable] = measureSharpness(___)`

measures the spatial frequency response (SFR) at all slanted edge regions of
interest (ROIs) of an Imatest`sharpnessTable`

= measureSharpness(`chart`

)^{®} eSFR chart.
`sharpnessTable`

includes the frequency for each ROI at which
the response drops to 50% of the intitial and peak values.

measures the SFR at all specified slanted edge ROIs, specifying additional
parameters.`sharpnessTable`

= measureSharpness(`chart`

,`Name,Value`

)

`[`

also returns the average SFR of vertical and horizontal ROIs, using the input
arguments of either of the previous syntaxes.`sharpnessTable`

,`aggregateSharpnessTable`

] = measureSharpness(___)

Slanted edges on a properly oriented chart are at an angle of 5 degrees from the horizontal or vertical. Sharpness measurements are not accurate when the edge orientation deviates significantly from 5 degrees.

Sharpness is higher toward the center of the imaged region and decreases toward the periphery. Horizontal sharpness is usually higher than vertical sharpness.

Perform sharpness measurements on linearized data. Use

`rgb2lin`

to linearize sRGB images.

The SFR measurement algorithm is based on work by Peter Burns [1]
[2]. First,
`measureSharpness`

determines the edge position with sub-pixel
resolution for each *scan line*, or row or column of pixels
perpendicular to the edge, in the ROI. For example, each row of pixels is a scan line
for a near-vertical edge. Next, `measureSharpness`

aligns and averages
the scan lines to create an oversampled edge intensity profile. The function takes the
derivative of the intensity profile and applies a windowing function. The returned SFR
measurement is the absolute value of the Fourier transform of the windowed
derivative.

[1] Burns, Peter. "Slanted-Edge
MTF for Digital Camera and Scanner Analysis." *Society for Imaging Science and
Technology; Proceedings of the Image Processing, Image Quality, Image Capture
Systems Conference*. Portland, Oregon, March 2000. pp
135–138.

[2] Burns, Peter. "sfrmat3: SFR evaluation for digital cameras and scanners." URL: http://losburns.com/imaging/software/SFRedge/sfrmat3_post/index.html.

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