Problem

Certain imatest calculations in version 5.1 and below produced zeros when the calculation was not determined. These zero values could be inappropriately averaged with summary metrics which lead to these summary metrics being underreported.

The problem includes, but is not limited to the following summary metrics:

• Chromatic Aberration (CA) summary calculations CA_areaPCT_summary, CA_crossingPCT_summary, CA_R_G_PCT_summary, CA_B_G_PCT_summary where the individual outputs in CA_area_Pct_corner, CA_cross_Pct_corner, CA_crossing_R_G_PCT_corner, CA_crossing_B_G_PCT_corner, CA_crossing_R_G_Pxls, CA_crossing_B_G_Pxls, include zeros.
• MTF Summary metrics where higher frequency MTF values that are not achieved, and incorrectly reported as zero (corrected in v5.1.28)

Solution

• Take care not to use any summary metrics where the calculations output zeros
• Upgrade to Imatest 5.2 where these indeterminate calculations are reported as NaN (Not a Number), and will not be included in any averages

On some MacOS systems, the 5.2 Imatest release has an issue where the system temporarily freezes for under 60 seconds when file dialogs are opened.

We have traced this to the new 2019a MATLAB compiler runtime and are working with MathWorks to resolve the issue. (more…)

Using testing charts (also known as targets) improves the efficiency and repeatability of your testing workflow. Imatest offers several charts that support automatic detection as well as charts with registration marks.

(more…)

In order to perform online license activation or to use a floating license, Imatest needs to be able to perform name resolution or connect through a network to the following licensing servers:

(more…)

Recently we have been receiving reports of end-users in China being blocked from accessing the Imatest license servers (IP address 184.106.60.185).

A message such as “SOAP couldn’t connect to host; Error code -4304″ may be displayed.

Here are the current workarounds to resolve this issue for this subset of end-users:

• End-users have had success using a VPN to tunnel to either another location within China that is not impacted by an ISP block, or outside of China. This is typically the easiest solution to address the issue.
• Use offline activation: The offline activation portal accessible through store.imatest.com is still functional.

Note: this offline activation approach works both for individual node-locked licenses as well as offline activation of network-based licenses within the Nalpeiron LAN Daemon – which then allows floating licensing, element pools, floating features, etc. all to be used within the application.

• There is a relay server with the IP address 119.9.127.11.  You can use the proxy address to 119.9.127.11 (port 80) and use that to redirect back to our standard servers.  
• Review our Connectivity requirements for online or floating license activation

We apologize for the inconvenience. Please contact us at support@imatest.com with any difficulties you have.

Color reference files read by Imatest can be CSV or CGATS format containing L*a*b* color and luminance reference data.

The reference illuminant is assumed to be the same as the selected color space (D65 for sRGB, etc.). This is at variance with current practice, where L*a*b* files are assumed to have D50 data. The new LAB D50 file (Imatest 4.4+) is recommended because it will transform the reference values using a Bradford Transform to move them to the selected color space’s white point. This is the recommended approach if you have spectrophotometer measurements for your individual chart.

Color Reference files

Color CSV reference files files consist of the number of lines that the test chart has patches, with L*, a*, b* values on each line separated by spaces, commas (,), or semicolons (;). Example (first 3 lines of 24):
38.08, 12.09, 14.39
66.38, 13.22, 17.14
51.06, 0.38, -22.06

If you have an Excel .CSV file with extra rows or columns, you can easily edit it Excel by selecting the key region (3 columns, 24 rows), copying it to a new file, and saving it in .CSV format. L*a*b* data is preferred to xyY data below because it is independent of white point color temperature, hence less error-prone. 

Color reference files can also be derived from measured values from a camera you determine to be a “gold standard” by running Color/Tone Interactive, then pressing File, Save L*a*b* results as CSV reference (making sure to check CSV reference file of L*a*b* results…). This can be useful for manufacturing testing because the camera under test is compared with the attainable values of a golden sample rather than unattainable ideal values.

The CGATS file format is also supported.

Color/Tone Interactive General mxn charts (4×12 shown on the left). Any chart with an m x n grid can be analyzed. You must specify the grid size (click Settings, ISO speed & mxn chart settings to set the number of rows (m) and columns (n). You must also enter a CSV or CGATS file with reference patch settings (typically L*, a*, b* values, one set per line). If you have a spectrophotometer you can create a custom reference file (CGATS format) using techniques described in Measuring test chart patches.

Density Reference Files

Density CSV reference files are much simpler, they contain one optical density value per line, going from least-dense (smallest) patch, up to the most dense patch.  

Imatest will provide you with a density reference file when you purchase a 36-patch dynamic range or contrast resolution chart. You should always use this reference file while performing dynamic range measurements with multicharts or color-tone instead of using the default values.

See Also

• Color/Tone Interactive Reference File 
• Colorcheck Reference File (to be deprecated at a future date)
• Measuring Test Chart Patches with a Spectrophotometer for details about how to create a reference file using measurements from an instrument.

by Henry Koren, inspired by Paul Romanczyk, edited by Norman Koren

Not all MTF measurement systems will necessarily provide the same results. The quality of the test target can impact the measurements you obtain. Long distance tests are ideally performed at the hyperfocal distance, where there is enough depth of field to have acceptable focus at infinity. (more…)

Here are Henry’s favorite Imatest Links that he often mentions during the Imatest Training Class:

Day 1

Day 2

https://imatest.com/passfail/

This guide enumerates the possibilities and constraints of our test charts and provides resolution (MTF) information for the different options. Imatest has introduced Chart MTF Compensation, which can as much as double the resolution suitability of a given test chart.

Inkjet

Close up of inkjet print quality

Inkjet is the lowest resolution process we offer, but also the least expensive and most versatile. The minimum print size with inkjet is approximately 8” x 10”, and the maximum print size for a single sheet is 44” x 80”.

Inkjet charts are available in three different substrates: Matte and Semigloss for reflective testing and DisplayTrans for transmissive tests using a backlight. All inkjet options are roughly the same resolution.

Inkjet is best suited for cameras tested at a moderate distance in order to compensate for the low resolution of the print. It is also suitable for low-resolution or wide-angle systems. As the resolution of the target is relatively low, the size of the chart needs to be larger to accommodate a higher resolution sensor.

We can produce custom charts, and custom sizes of most of our standard charts. Contact charts@imatest.com with your requested size and information about your lens (field of view and testing distance) and sensor (pixel count and aspect ratio.) We need the pixel count to confirm the size you are requesting will be adequate for your imaging system. Our Chart Finder Tool can help you determine the size of your imaging plane at a specific testing distance.

Photographic Paper (Silver Halide)

Close up of photographic paper print quality

Photographic media offers high-resolution reflective prints when a transmissive target is not an option. These prints are over twice the resolution of inkjet media.

The minimum size of a photographic print is approximately 8” x 10” and the maximum size is approximately 40” x 50”.

Our standard photographic targets include our eSFR ISO chart (3 sizes) and a multi-size option of our SFRplus chart. This multi-size is best suited for testing low-resolution systems at close distances. We can offer custom charts on this media for an additional fee. Contact charts@imatest.com for information. 

Transmissive Photographic Film

Our Color and Black & White film targets are printed using high-precision LVT Technology. These transmissive targets require a lightbox in order to be used properly. 

Black and White

Close up of Black and White Film print quality

Black and White film is over twice the resolution of our inkjet targets, and can optionally include a color patch for color measurements. The size of the film is 12” x 20” or 16” x 20” (with ½” on each side as unprintable area). The minimum target size on this media is roughly 2” x 3”. We can print multiple targets on a single sheet of film depending on the size and resolution requirements to help make this option more cost-effective.

This media is suited for customers testing in a small area with low to medium resolution cameras.

Color

Close up of Color Film print quality

Our high-precision color film targets are printed on 8” x 10” film with a maximum printed area of 9.25” x 7.75”. The minimum target size on this media is approximately 0.5” x 1”. As with the Black and White film, we can print multiple targets to a single sheet of film to make this a more cost-effective option.

This media is suited for customers requiring a very compact testing system or those using conversion optics to simulate infinity within a very small space. The fine detail of the film allows us to test mid to high-resolution cameras at close distances and with a small field of view. Color film has the highest dynamic range of all of the targets we offer. 

Chrome on Glass Photomask

Close up of Chrome on Glass print quality

Chrome Photomasks are our sharpest option for resolution testing. We use a lithographic photomasking process to print chrome directly onto glass. This process is single tone, so there is no gray-scale or tonal variance.

Chrome on Glass offers superior resolution when color and tonal measurements are not needed. We can make targets as small as 2mm x 3mm for measuring devices such as endoscopes or microscopy equipment. When printing to glass, the chrome has an optical density of 1, which gives a contrast ratio of approximately 10:1, suitable for resolution measurement.

Our standard glass plates are 4” x 4” with a non-printable border of 1 cm. We can source plates up to 20” x 20” and as small as 1” x 1”. Any plates larger than 4” x 4” require an extended lead time of 6-8 weeks. 

We can customize the size of various targets such as our SFRplus or ISO-eSFR targets on request. We can also print most custom design requests to glass, though some may require an engineering fee depending on the complexity of the design. Contact charts@imatest.com.

Abstract

By Robert Sumner

With contributions from Ranga Burada, Henry Koren, Brienna Rogers and Norman Koren

Consistency is a fundamental aspect of successful image quality testing. Each component in your system may contribute to variation in test results. For tasks such as pass/fail testing, the primary goal is to identify the variation due to the component and ignore the variation due to noise. Being able to accurately replicate test results with variability limited to 1-5% will give you a more accurate description of how your product will perform. (more…)

If upon opening Imatest you get something like this:

Error: Error using load
Unable to read MAT-file C:\ProgramData\Imatest\mcr_cache\5.0\Master\mcrCache9.2\imates0\.matlab\matlabprefs.mat. File might be corrupt.

Some of your MATLAB files have become corrupted. You can solve this by deleting your CTF folder found at C:\ProgramData\Imatest\mcr_cache\5.0\Master\, then try starting Imatest again.

If you continue to have problems please email us with details of the issue at support@imatest.com

With the addition of python routines in Imatest 5.0, several components require a working python installation. When some installation problems occur, the user may encounter the error message:

Undefined variable “py” or class “py.model.Message”.

Solution 2:

The obsolete ISO 12233:2000 standard defines a resolution test target with a high contrast ratio. These are typically produced at the maximum dynamic range of a printer, which can be anywhere from 40:1 to 80:1.  The high contrast can lead to clipping of the signal which leads to overstated invalid MTF values. (more…)

Due to High Sierra’s new file system, old Imatest licenses no longer have the access they need to write properly.

If your Imatest license begins with the numbers 2848 and you are trying to run on OSX High Sierra or later please let us know with your license included at support@imatest.com

Imatest is still working on implementing RTSP streaming support and other video stream protocols within the software. In the meantime if your streaming protocol has the capability of outputting MP4s or other common video file formats, you can load this video into Imatest to analyze. Alternatively, you can use a program like FFMPEG or VLC to split the video into its individual frames, then analyze the frame as an image in Imatest. Heres how.

Using FFMPEG

1. Download a static FFMPEG build from a reputable source.
2. Install FFMPEG according to the directions of your current OS:

Windows:

1. Use a program like 7-Zip to unpack the files to your preferred location.
2. Open up the command line with administrative privileges.
3. Run the command:

setx /M PATH "path\to\ffmpeg\bin;%PATH%"

OSX:

a. Install homebrew by running the following in a terminal:

/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

b. Once homebrew is installed, just enter in a terminal:

brew install ffmpeg

Linux:

a. Install ffmpeg

sudo add-apt-repository ppa:mc3man/trusty-media
sudo apt-get update
sudo apt-get install ffmpeg
sudo apt-get install frei0r-plugins

b. With FFMPEG installed you can now call it from a command line or bash terminal to split your video file into frames:

ffmpeg -i myfile.avi -f image2 image-%05d.png

Using VLC

coming soon

Megapixel suitability is based on the analysis of the Modulation Transfer Function (MTF) that is obtained from slanted-edge chart images captured at magnifications of around 0.5× (for inkjet charts) or 1× (for photographic charts) using a high quality DSLR or mirrorless camera and macro lens.

The calculations are described in the following links:

• Compensating camera MTF measurements for chart and sensor MTF (Imatest 5.1+); i.e.,  Introduction, Calculation, MTF compensation files, Applying the compensation, and Lens MTF measurements sections.
• Chart Quality Calculator (Imatest 5.1+)—determine the suitability of a chart (based on MTF measurements for specific media and print methods) for a specific application.
• Test chart suitability for MTF measurements—charts for determining the MTF measurement suitability of several media types (inkjet and photographic; reflective and transmissive); based on Chart Quality Calculator results.

Note: the old Chart Quality Index (CQI) calculation has been deprecated.

Megapixel suitability is based on the spatial frequencies where the projected chart MTF on sensor is 0.9 at the Nyquist frequency (0.5 cycles/pixels). We’ll omit the details of the calculations here. The beauty of the new approach is that megapixel suitability can be determined from just three items:

1. File (the chart MTF compensation file) that has a model of the chart MTF (measured in cycles per object mm).
2. Pixel height of the image sensor.
3. Vertical Field of View of the camera, typically somewhat larger than the height of charts designed to fill the frame (SFRplus, eSFR ISO, etc.).

We use the Chart suitability display for Black and White LVT film (which is very much sharper than inkjet prints) as an example.

The standard Black & White LVT chart, printed on 12 inch × 20 inch film, is designed to have a 27cm vertical field of view; 27cm (on the x-axis) corresponds to MTF@Nyquist = 0.9 (the green diagonal line, below) for sensor height = 5500 pixels (left y-axis) or 45 megapixels at 3:2 aspect ratio (right y-axis). At this high quality level, MTF compensation is not required. If we push the chart to MTF@Nyquist = 0.7 (the olive diagonal line), which is still reasonably good, but requires MTF compensation, we reach sensor height = 8500 pixels (about 100 Megapixels at 3:2 aspect ratio).

Chart suitability display for B&W LVT film. Click image for full-size view.

The Megapixel suitability calculation shown here assumes that:

1. The lens is of high quality.
2. The sensor aspect ratio is 3:2, which can be changed in the box on the right. The change only affects the Megapixel numbers; i.e., Megapixel suitability, on the right y-axis.

For 16:9 aspect ratio sensors, multiply the megapixel suitability by 1.185.
For 4:3 aspect ratio sensors (with left/right sides of chart cropped), multiply megapixel suitability by 0.889.

Additions to Imatest 5.1

Imatest 5.1, released in April 2018, has an important enhancement that increases the megapixel suitability of most Imatest charts by up to a factor of 2. The MTF for most charts, which is a function of the chart media and printing technique, has been measured and fit to a simple two-parameter function that can be used to correct MTF measurements by deconvolution (by dividing the measured camera+chart MTF by the chart MTF function projected on the image sensor). The correction can be applied by entering an MTF correction file into the settings windows for any MTF calculations. For more details, see Compensating camera MTF measurements for chart and sensor MTF.

A Chart Quality Calculator that uses the new MTF functions is also available. It provides a clearer and more accurate estimate of MTF suitability (including the expected MTF loss from the media with and without the correction) than the older Chart Quality Index.

Chart suitability displays for several media types are found in Test chart suitability for MTF measurements.

See Also

• Transmissive Chart Quality Comparison
• Reflective Chart Quality Comparison: Inkjet vs. Photographic
• ISO 12233:2017 Edge SFR (eSFR) Photographic chart
• ISO 12233:2017 Edge SFR (eSFR) Inkjet chart

*measured using 9 rectangular regions, as described below.
** measured using 30-10,000 lux model, ultra bright version has 90% uniformity

Lightbox Uniformity- Detailed Measurements

For the key measurement, the definition of uniformity is

Uniformity = 100%*(1 – (maximum of 9 regions- minimum of 9 regions) / maximum of 9 regions)

where the 9 rectangular regions (shown in the figures below) include the top, bottom, left, right, 4 corners, and center. The rectangular region dimensions are 10% of the crop width and height and (except for the center region) they are located 5% of the width and height from the boundaries, as described below.

Click on any of the images below to view full-sized.

ITI LED Lightbox Uniformity = 95.2% Response is very even, but unusual in that the center is slightly dimmer than the top and bottom. Note that the contour line increments are 0.01 (1%), lower than the other lightboxes because the ITI is much more uniform. (0.02 contour increments wouldn’t show very much.) The lightbox spectra for the standard 3100K and 5100K settings, provided by ITI, are shown below.
GTI GL-16e Lightbox Uniformity = 63.6% The contour line increments are 0.02 (2%), double that of the ITI LED Lightbox. Both the GL-16e and GLX-30 have very wide aspect ratios. Their uniformity would be much better if less of the sides were included in the measurement.
Artograph 930 12×9 inch Light Pad We use this inexpensive lightbox for non-critical applications like MTF measurements and for trade show demonstrations. It’s uniformity is quite good. Uniformity = 77%
Artograph 950 24×17 inch Light Pad We use this large, relatively inexpensive lightbox for non-critical applications like MTF measurements and for trade show demonstrations. It’s uniformity is quite good. Uniformity = 78.5% (Figure is darker because image was less exposed.)
The control The control for these measurements was made by capturing images immediately in front of the ITI lightbox (no more than 1cm distant). Results were repeatable when the camera was moved around the lightbox. Contour increments are very small: only 0.002 (0.5%). Uniformity = 98.75%
GTI GLX-30 Lightbox (No longer available in the Imatest Store) Uniformity = 70.1% The contour line increments are 0.02 (2%), double that of the ITI LED Lightbox.
GTI GLE 12e Lightbox (No longer available in the Imatest Store) Uniformity = 65.8% The contour line increments are 0.02 (2%), double that of the ITI LED Lightbox.

How we made the measurements

We developed a methodology for measuring lightbox uniformity because we were not aware of any relevant standards.

• Photograph the lightbox using a camera with a long focal length marco lens. Such lenses tend to be highly uniform, i.e., have very low vignetting. We used the Canon EOS-6D with the highly-regarded 100mm f/2.8 macro lens set at f/8. Be sure to capture raw images. We used manual focus because the EOS-6D didn’t focus well on this image.
• Frame the lightbox so it occupies about the central 30% of the image (10% by area). This makes the already low vignetting insignificant. Here is the framing (and region selection) for two lightboxes.

Click on the images to display them larger.

ITI Lightbox

GTI Lightbox

• Open Uniformity (or Uniformity Interactive) and read in the raw file, converting it to a gamma = 1 (linear) file. (This means it’s not a standard file, but pixel level will be proportional to illumination.) Here are the recommended settings from the Imatest dcraw GUI window. The key settings are Output gamma = 1.0 (Linear), Auto white level checked, and Normalize by 1.0.

• Crop the images just inside the bright areas of the lightbox, as shown above. If there are areas of rapid illumination falloff close to the edges of the lightbox image, it’s OK to omit them.
• Click Yes to open the Uniformity settings box. The key settings are shown inside the red rectangles. The corner and side regions (the rectangles) are 10% of the ROI (linearly), and the location of the regions is 5% (of the ROI size) from the ROI boundaries. We feel this is a reasonable summary metric since most tone and color measurements are made in the central two-thirds of the image. Uniformity is more important when measuring tone and color than it is for MTF, even though Imatest corrects for patch nonuniformity due to vignetting and uneven illumination.

• After you click OK (not shown) Uniformity runs and the results figures appear. The key nonuniformity summary metric does not appear in the figures it’s in the CSV and JSON file output. Here is the relevant CSV output.

  Uniformity = 100%*(1 – (maximum of 9 squares – minimum of 9 squares) / maximum of 9 squares)

• and here is the JSON output:

         “nonuniformity_LRTB_sides_ctr_pct”: [36.4],
         “uniformity_LRTB_sides_ctr_pct”: [63.56],

Abstract

The dynamic range of recent HDR image sensors, defined as the range of exposure between saturation and 0 dB SNR, can be extremely high: 120 dB or more. But the dynamic range of real imaging systems is limited by veiling glare (flare light), arising from reflections inside the lens, and hence rarely approaches this level. (more…)