Connectivity requirements for online or floating license activation

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:

Server Name IP Address Port Protocol
login store.imatest.com 216.55.185.175 443  https
license my.nalpeiron.com 184.106.60.185 443 https

 

You can allow these in your network policy or use a proxy server which has the ability to connect, or you can use the proxy address 119.9.127.11

If name resolution is disabled, you can use a hosts file with the following contents:

216.55.185.178 store.imatest.com
184.106.60.185 my.nalpeiron.com

You cannot access the license server in mainland China: please see this post.

Still having problems? Contact us at licensing@imatest.com

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Users in China having problems activating licenses or starting trials

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.

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

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Color & density reference files in CSV or CGATS format

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 Multicharts, then pressing FileSave 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.

Multicharts 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 SettingsISO 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 multitest instead of using the default values.

See Also

 

Read More

Understanding collimator MTF loss using bronze and golden sample testing

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. Long-range tests which exceed the available space within your lab or factory are the most challenging. A collimator or relay lens system can be used to produce virtual targets at a simulated distance. The measurements obtained through a collimator can diverge from measurements obtained from free-space test targets. This article will discuss how to cope with that.

(more…)

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Henry’s Imatest Training Links

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

Day 1

Day 2

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Test Chart Substrate and Sizing Guide

This guide enumerates the possibilities and constraints of our test charts and provides resolution (MTF) information for the different options.

Inkjet

Close up of Inkjet Print Process Quality

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.

Test extremely wide-angle imaging systems with a multi-sheet target. The constraints of this process are the number of columns that can print on each sheet. The tiled pieces of this chart must be assembled on site by the customer due to the extremely large sizes. We have produced charts as large as 80” x 120” using this process. 

 

Photographic Paper (Silver Halide)

Close up of Photographic Paper print quality

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

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.

For high-resolution systems, we can tile together multiple pieces of LVT film to fit the size of your lightbox. The maximum dimensions using this option are approximately 19” x 32”. This option is best suited for customers testing high-resolution cameras such as DSLR’s. 

 

Color

Color Film Print Quality

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

Chrome on Glass Print Quality

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.

 

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Reducing the cross-lab variation of image quality metrics

Abstract

As imaging test labs seek to obtain objective performance scores of camera systems, many factors can skew the results. IEEE Camera Phone Image Quality (CPIQ) Conformity Assessment Steering Committee (CASC) working group members performed round-robin studies where an assortment of mobile devices was tested within heterogeneous imaging labs. This paper investigates how the existence of near-infrared energy in light sources that attempt to simulate CIE illuminants can influence test results. Numerous other impacts, including the influence opal diffusers used for uniformity testing, how test scene framing can alter white balance and exposure, and how chart quality and texture frequency distribution can skew results. We introduce a test procedure which is intended to reduce intra-lab variability and a method for assessing an independent lab’s competence in conforming with the IEEE testing standards.

(more…)

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New 2019 Imatest Licensing – Update Required to Activate

We are migrating to a better, faster licensing platform for our software on January 1, 2019. You may need to update your software to activate it on a new device, depending on your software version. Updating your software is free of charge.

Who is affected by this?

If your license code starts with 2848, you will need to update your software after January 1, 2019 if you need to install it on other devices or reactivate it on a current device. Your software will continue to work as normal until you need to reinstall or reactivate.

What actions do you need to take?

You will need to update your software in order install it on other devices or reactivate it on your current device. Check below for your software build download link. If you’re not sure which version you need, contact us.

What happens if you don’t update?

You can continue to use your software as it is without updating it. However, if you attempt to reactivate it or install your software on another device after January 1, 2019, you won’t be able to do so. You’ll need to update the software to continue using it.

What are the benefits of this?

  • Our licenses will now run properly on OSX versions High Sierra and higher.
  • Our licenses will have fewer issues activating on machines with heavy security and those that run in offline environments.

What version do you have?

As a reminder, this applies to licensing codes starting in 2848 only.

On opening Imatest, the version you are running will be displayed at the top of the main screen, in the command window, or in the Help > About window.   imatest software not upgrading

Download your software update today.

Select your software version from the drop-down menu below to access your download link.

 

PLEASE NOTE: The above links are upgrade installers. If you require the full build, you may download it from our Software Download page.

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Increasing the Repeatability of Your Sharpness Tests

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.

Since Imatest makes measurements directly from the image pixels, any source that adds noise to the image can affect measurements. A primary source of noise in images is electronic sensor noise. Photon shot noise also contributes significantly in low-light situations. Other systemic sources of measurement variability, such as autofocus hysteresis, will not be addressed in this post.  

In order to reduce variation in your sharpness results and increase test repeatability, you should take steps to decrease the amount of noise in your image.

Here are 5 tips to limit noise in your test results: (more…)

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Imatest does not start, unable to read MAT-file

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

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

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”.

This is generally caused by Imatest being unable to locate the correct python interpreter, or python failing to install properly.

Solution 1:

Make sure the python interpreter was installed properly and that you have permissions to access it. It should install to:
 
C:\Program Files\Imatest\v5.0\Master\bin\python35
 

Solution 2:

Some customers get this error when they try to run python:
 

To resolve, Reinstall the Visual Studio C++ 2013 redistributable, this is in the Imatest installer or you can install it directly from Microsoft: VS 2013
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High-contrast edge-SFR test targets produce invalid MTF results

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.

Some camera manufacturers who want better MTF results may take advantage of this anomaly to overstate the quality of the cameras they produce. This is why it is critical to validate cameras with a proper measurement system that includes a low-contrast target. (more…)

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Running Imatest With High Sierra

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

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How to capture frames from a video stream or RTSP camera

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

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Megapixel suitability for test charts

 

Megapixel suitability is based on analysis of Modulation Transfer Function (MTF) 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+)

Introduction – Calculation – MTF compensation files – Applying the compensation – Lens MTF measurements

Chart Quality Calculator (Imatest 5.1+) – determine the suitability of a chart (based on MTF measurements for specific media & 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 that 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.

  • a file (the chart MTF compensation file) that has a model of the chart MTF (measured in cycles per object mm).
  • the pixel height of the image sensor
  • the 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 12×20 inch film, is designed to have a 27 cm vertical Field of View. 27 cm (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 on image for full-size view.

The Megapixel suitability calculation shown here assumes that:

  1. the lens is of high quality
  2. that the sensor aspect ratio is 3:2. (it can be changed in the box on the right. The change only affects the Megapixel numbers, i.e., Megapixel suitibility, 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 which 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.

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 without and with 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

Read More

Lightbox Uniformity Comparison

 

Lightbox Brightness Uniformity* CRI (spec.)
Viewing Area Dimensions Controls
Imatest LED Lightbox 1 to 100,000 lux ** 90 to 95% Over 97

260 x 220 mm to 1440 x 1100 mm (9 Sizes)

400 (W) x 380 (H) x 200mm (D) to 1655 x 1296 x 200 mm (9 Sizes) WiFi, USB, Manual
Imatest LED Light Panel 30 to 1,000 lux 90 to 95%   229 x 152mm to 907 x 680mm (5 Sizes)
289 x 212 x 40mm to 967 x 740 x 55mm (5 Sizes)
WiFi, USB, Manual
IQL LED Lightbox 10 to 40,000 lux     254 x 279.4mm 472.4 x 383.5 x 129.5mm Wireless via Android
GL-16e Lightbox Viewer 5750 lux 63.6% 96-98 10 x 18″ (25 x 46 cm) 15x25x5″ (38x64x13cm) Manual
GL-20e Lightbox Viewer            
GL-30e Lightbox Viewer            
GL-44e Lightbox Viewer            
GLX-3044 Lightbox Viewer N/A N/A 96-98 30×42″ (76x107cm) 35x49x5″ (89x124x13cm) Manual
GLX-3856 LIghtbox Viewer N/A N/A 96-98 38×56″ (96x142cm) 43x63x5″ (109x160x13cm) Manual
GLE-10 Lightbox Viewer N/A TBC 96-98 8×10″ (20x25cm) 15.5×12.25×3.25″ (39x31x8cm) Manual
GLE GLX-30 Lightbox Viewer 5000 lux 70.1% 96-98 16″ x 30″ (41 x 76cm) 21 x 37.5 x 5″  Manual
Artograph LightPad® 930 2820 lux  77%   12×9″   On/Off
Artograph LightPad® 950 2740 lux 78.5%   24×17″   On/Off

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

 

A better color quality measurement?  The color quality of light sources is traditionally measured by CRI (Color Rendering Index), which has a maximum value of 100 (%). Recently, doubt has been cast on the accuracy of CRI, and a new Color Rendition measurement has been proposed: IES TM-30-15. It’s unfamiliar and the linked document doesn’t have an equation or algorithm for calculating it from the light spectrum. We’ll wait and see…

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.

ITI_uniformity_contours
ITILED-3100k ITILED-5100k

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.

 

GTI_GLX16e_uniformity_contours

   

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_12x9_uniformity_contours

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.) 

Arto_950_uniformity_contours

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%

EOS-6D_closeup_uniformity

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_GLX30_uniformity_contours

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.

GTI_GLX12e_uniformity_contours

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_uniformity_cropITI Lightbox GTI_uniformity_cropGTI 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.

lightbox_dcraw_settings

  • 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.

lightbox_uniformity_settings

  • 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)

Nonuniformity LRTB sides ctr (%) 36.44
Uniformity LRTB sides ctr (%) 63.56
  • and here is the JSON output:

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

 

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Measuring the impact of flare light on dynamic range

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. Veiling glare measurements, such as ISO 18844, made with black cavities on white fields, result in large numbers that are difficult to relate to dynamic range. Camera dynamic range is typically measured from grayscale charts, where veiling glare depends on the design and layout of the chart, leading to inconsistent results. (more…)

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How to convert a color image to grayscale

Sometimes an undemosaiced Bayer raw image gets improperly saved into a BMP or TIFF format that includes color channels that are all equal. In this case, Imatest will recognize the image as color, and not give you the monochrome read options that allow you to perform demosaicing or analyze the image as a Bayer raw.

Here are a variety of ways to convert a color image to grayscale:

Imagemagick command line utility

$ convert -type Grayscale rawcolor.bmp mono.bmp

GIMP / Photoshop

Image -> Mode -> Grayscale

 

ImageJ

From Image -> Tyoe -> Select the desired output bit depth

Irfanview

Ctrl-G or from the image menu select Convert to Grayscale

MATLAB

img = imread('rawcolor.bmp');
r = img(:, :, 1);
imwrite(r, 'mono.bmp');

 

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Avoiding reflections on transmissive charts for dynamic range and flare testing

The testing of dynamic range and flare requires a proper test chart and environmental setup to get accurate results.High precision and high-density chart technologies such as photographic film or chrome on glass come with the disadvantage of glossiness which makes them susceptible to specular reflections on the target. This affects the use of dynamic range or contrast resolution and backlit flare targets that lack anti-reflective patches. 

The goal of the backlit test setup is to maximize the fraction of light that is coming directly from your light source, through your test target, and into your lens, Any additional light that is present in your system can disrupt your measurements either by causing reflections on the analysis patch of your target, or otherwise introducing additional flare (veiling glare) into the image.

As the optimal lens and camera body housing will be manufactured with anti-reflective coating, it is good to take a similar approach with your test environment.  Nothing is actually entirely black, but dark, opaque materials come in many different forms. These can be characterized by their total hemispherical reflectance (THR).

Here are how some dark materials compare:

Product THR (vis+NIR) Notes
Black Paint 5-6% Not dark enough
Black Felt 2.5% Flexible and low-cost
Acktar black 1.5% Comes on adhesive foil
Vantablack 0.17% Costly, not durable, dangerous to humans

For general testing purposes, we use black felt for covering our darkened test box

Block all light from entering or reflecting inside the testing environment

For accurate testing, you should create a dark space where no outside light is able to enter, and as much internally generated light is absorbed. Here is a diagram of a test environment:

Minimize internal direct reflections

The more that the surfaces in your test environment are lit up, the more they will become reflections in the glossy chart.

The body of the camera under test or even just glass of a camera lens can reflect back onto a test chart.This is especially important incident towards dark analysis regions.

If using Imatest charts that are properly centered, the reflection might not fall on to a dark analysis region for dynamic range measurement. Here is an example of a reflection of a dev kit PCB that would disrupt dynamic range or contrast resolution measurement:

Reflective camera parts should be blocked by black masks. The entire area behind your camera will directly be reflected back, so this environment should be made as dark as possible.

Minimize other internal light emissions

Sensor development kits often have blinking LED’s that reflect directly, Front facing cameras with displays that are not disabled or blocked off can be particularly problematic.

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DMX Lighting Control Software

Lights such as the Kino Flo Select 31 LED use a DMX control interface to signal changes of light level and color temperature.

DMX is an open protocol and there are a large number of possibilities for hardware and software control. I’ve tried out several of these are more oriented to stage control
 
For DMX controller hardware I have personally tried and will recommend the Enttec DMX USB Pro controller worked well for us.
For computer control software with a user Interface, the one that has worked best for me so far is the Q Light Controller Plus (QLC+) which has nice cross-platform support.
 
For light control software that provides an automated API, the best one I have found, and the one we use to automatically control lights in our lab is the Open Lighting Architecture (OLA). The downside of this is that it only has good support for Linux. I have attached a python script that includes an example OLA calls, along with calls to an isolight puck, which you can overlook.  Here is a basic call to set the lights to middle color temp and maximum intensity:
 
from ola.ClientWrapper import ClientWrapper
intensity = 255
cct       = 127
universe = 1
data      = array.array('B') 
data.append(intensity)
data.append(cct)
data.append(intensity)
data.append(cct)
wrapper = ClientWrapper()
client = wrapper.Client()
client.SendDmx(universe, data, DmxSent)
 
Our goal for Imatest 5.3 is to have an instrument control interface built into Imatest Master that can directly communicate with DMX hardware.

 

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