Imatest Documentation

Imatest Documentation
Explanation of results
Megapixels The total megapixel count for the camera.
Picture height
pixels
Oversharpening %
10-90% rises per
PH (raw)
10-90% rises per
PH (corr.)
MTF50
LW/PH
(raw)
MTF50
LW/PH
(corr.)
Chromatic
aberration (CA)
Shannon
capacity
MB
Comments
Tables of results
The picture height of the camera. Important because sharpness is measured in units of Edge Rises or
Line Widths per Picture Height.
The amount of sharpening relative to standardized sharpening, which results in a modest amount of
overshoot, similar to what you might get after manually sharpening the image. Undersharpening (as
reported in Imatest SFR) is displayed here as a negative number.
The number of intervals per Picture Height where the average edge signal (with gamma removed) rises
from 10% to 90% of its final value. The more the better, though aliasing can be a problem for extremely
high values (significantly larger than the picture height), especially with Bayer sensors. See
Understanding sharpness and SFR tour.
The number of 10% to 90% rise intervals per Picture height after standardized sharpening. This allows
cameras with different degrees of sharpening to be compared on a (relatively) fair basis. A sharpening
radius of 2 is assumed, unless indicated below. This radius works well for oversharpened compact
digitals, but radius = 1, used by Imaging-resource.com, may be more appropriate for find DSLRs.
The spatial frequency where contrast drops to half its low frequency value. This is the best indicator
of sharpness. See Understanding sharpness and SFR tour.
MTF50 with standardized sharpening applied (corrected). MTF50 with standardized sharpening is best
for comparing cameras with different amounts of sharpening; MTF50 without standardized sharpening
(uncorrected) is best for testing and comparing lenses on a single camera model. See note on
sharpening radius, two rows above.
A measure of "color fringing" near the edges of the images. Units are pixels. Tends to increase linearly
with the distance from the center of the image. Under 0.5 pixels is insignificant. Over 1.5 is severe: quite
visible in large prints. See Chromatic Aberration. An improved CA measurement, percentage of
distance from the image center, is being implemented.
The information capacity of the image, based on sharpness (with standardized sharpnening) and noise.
It correlates well with perceived image quality. But it should be interpreted with caution because it is
strongly affected by signal processing, especially noise reduction. Best when used with RAW files. The
number below is for a signal with the same contrast (100%) as the target (around 80:1). Shannon
capacity is a relatively new measurement. We are still learning how to interpret it.
Contains the source of the image (DPR or IR), and, if available, the focal length, aperture, and ISO
speed.
DSLRs: Digital SLRs, which take interchangeable lenses. Used by professionals and serious amateurs. Sensor size is at least 22 mm
diagonal. Larger and heavier than the compact digital cameras, below. This table is more complete than the table for compact
digitals because it's where my interest lies (and there are far too many compacts to keep up with). For each camera, the results in
the upper and lower rows are for the image center and edge, respectively, as illustrated here.
Reminder: Remember the limitations listed above: one lens, one focal length, one aperture, one ISO speed, one RAW
converter & settings (usually) built-in, one sharpening radius (2 unless otherwise indicated), etc., when interpreting
these results. Also remember that several important image quality factors such as noise and dynamic range have been
omitted.
Camera
Canon EOS-1D Mk II
Canon EOS-1Ds
MegaOver- 10-90% 10-90% MTF50 MTF50 Chro- Shannon
pixelssharp rises/PH rises/PH LW/PH LW/PH matic capacity
ening % (raw) (corr.) (raw) (corr.) Aber- MB
Picture
ration
height Center Ctr Ctr Ctr Ctr Ctr Ctr
pixels
Corner Cor Cor Cor Cor Cor Cor
Comments
8.2 -15 1351 1741 1355 1559 — 5.56 DPR. 50mm f/9 ISO 100. Very little built-in
sharpening. Optimized for speed. Same pixel
2336 -21 1178 1589 1173 1443 0.40 4.99 count as EOS-20D, but larger pixels.
11 -17 1509 2045 1521 1860 — 7.11 DPR. 100mm f/9 ISO 100. 24x36 mm sensor.
Little, if any, built-in sharpening.
2704 -17 1485 2016 1519 1852 0.30 7.06
Canon EOS-1Ds Mk II 16.7 -16 1919 2520 1922 2240 — 11.0 DPR. 50mm f/9 ISO 100. 24x36 mm sensor.
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