Imatest Documentation

Imatest Documentation
Pixel size has an important relationship to image quality. For very small pixels, noise,
dynamic range and low light performance suffer. Pixel size is rarely given in spec sheets: it
usually takes some math to find it. If the sensor type and the number of horizontal and
vertical pixels (H and V) are available, you can find pixel size from the table on the right and
the following equations.
pixel size in mm = (diagonal in mm) / sqrt(H 2 + V 2 )
pixel size in microns = 1000 (diagonal in mm) / sqrt(H 2 + V 2 )
Pixel size in microns (microns per pixel) can be entered directly into the SFR input dialog
box. Example, the cute little 5 megapixel Panasonic Lumix DMC-TZ1 has a 1/2.5 inch
sensor and a maximum resolution of 2560x1980 pixels. Guessing that the diagonal is 7 mm,
pixel size is 2.1875 (rounded, 2.2) microns.You can find detailed sensor specifications in
pages from Sony, Panasonic, and Kodak.
Sensor
Diagonal Width Height
Designation
mm. mm. mm.
(Type)
1/4" 4.5
1/3.6" 5.0 4.0 3.0
1/3.2" 5.68 4.54 3.42
1/3" 6.0 4.8 3.6
1/2.7" 6.59 5.27 3.96
1/2.5" 6.9 - 7.2
1/2" 8.0 6.4 4.8
1/1.8"
8.93 -
9.1
7.18 5.32
2/3" 11.0 8.8 6.6
1" 16.0 12.8 9.6
4/3" 22.5 18.0 13.5
35mm 44.3 24.0 36.0
For the Multi-ROI plot you can choose between Off, 1D plots (results as a function of center-corner distance with MTF in Cycles/Pxl,
LW/PH), 2D image plots (results superimposed on image with MTF in Cycles/Pxl, LW/PH). You can also plot multi-ROI SQF
(Subjective Quality Factor), which is explained here.
Noise spectrum and Shannon capacity is unchecked by default because the results are difficult for most users to interpret and may not
be meaningful, especially when significant noise reduction has been applied. It will not be plotted if the selected region is too small
for adequate noise statistics. If both Chromatic Aberration and Noise spectrum and Shannon capacity are checked, the two plots share the
same figure: CA on top and Noise/Shannon capacity at the bottom.
Display options (to the right of Plot) are settings that affect the plot display.
Secondary readout controls the secondary readout display in MTF
plots. The primary readout is MTF50 (the half-contrast spatial
frequency). Three secondary readouts are available with several
options. The first defaults to MTF30 (the spatial frequency where MTF
is 30%). The third is used only for SFRplus Lens-style MTF plots.
Clicking Change opens the window shown on the right. Secondary
readout settings are saved between runs. Choices:
The upper radio button (MTF) for each readout selects MTFnn,
the spatial frequency where MTF is nn% of its low frequency
value.
The middle radio button selects MTFnnP, the spatial frequency
where MTF is nn% of its peak value: useful with strongly
oversharpened edges.
The lower radio button (MTF @ ) selects MTF @ nn units, where
nn is a spatial frequency in units of Cycles/pixel, LP/mm, or LP/in.
If you select this button, the pixel spacing should be specified in
the Cycles per... line in the Plot section of the input dialog box,
shown above. A reminder message is displayed if the pixel spacing has been omitted.
MTF plot freq selects the maximum display frequency for MTF plots. The default is 2x Nyquist (1 cycle/pixel). This works well
for high quality digital cameras, not for imaging systems where the edge is spread over several pixels. In such cases, a lower
maximum frequency produces a more readable plot. 1x Nyquist (0.5 cycle/pixel), 0.5x Nyquist (0.25 cycle/pixel), and 0.2x Nyquist
(0.1 cycle/pixel) are available.
Edge plot selects the contents of the upper (edge) plot. The edge can be cropped (default) or the entire edge can be displayed.
Three displays are available.
1.
2.
Edge profile (linear) is the edge profile with gamma-encoding removed. The values in this plot are proportional to light
intensity. This is the default display.
Line spread function (LSF) is the derivative of the linear edge profile. MTF is the fast fourier transform (FFT) of the LSF.
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