Documentation

Arbitrary Charts

Combine all the features you need to analyze into a single chart

Introduction

The Imatest™ Arbitrary Charts module  analyzes images of custom, user defined test charts for a variety of image quality factors. With new chart layout concepts, users can obtain measurements for sharpness, noise, color error, texture response, dynamic range, white balance, and more. A chart-definition file, which may be created by the user to match their own design, is needed to describe the new chart layout concept to Imatest software. The Arbitrary Charts module will automatically locate and analyze target features when an observed image of a chart is loaded along with the corresponding definition file. 

The Arbitrary Charts module is a way of measurements from Imatest from test charts which we do not currently support in other modules, as long as they are composed of only a certain set of features (described below). It is available in both Imatest Master and Imatest IT. 

 

Getting started

Arbitrary Charts (Beta release) Quickstart

  • Create a JSON Definition file, according to the instructions in Arbitrary Chart Definitions.
  • Photograph the chart, using even glare-free lighting. The image does not have to fill the frame.
  • Manually set your INI-file options, or skip this step and use the defaults.
  • Open the Arbitrary Charts Module via the button on the main Imatest window. Load the test image(s) and the chart definition file. 
  • A JSON with measurement results will be produced for analysis by humans or an automated system.
 

 

Supported Target Features

The following set of features can be added to chart designs and analyzed with the Arbitrary Charts module. This is a growing list, with new features added with new software releases. See the Arbitrary Chart Definitions page to learn about the attributes for each feature.

 

Slanted square features yield four slanted edges, each of which can be used to produce slanted-edge MTF (e-SFR) results.

 

Individual slanted edge features which can produce an e-SFR result. 

Registration marks, used for automatic registration of the chart design with the test image. 

Color patch features (grayscale and chromatic) which can be used to measure color errors, tonal response, noise, and dynamic range. 

Random texture patch features which can be used to derive “Texture MTF” results. 


Arbitrary Chart Definitions

For Imatest to automatically locate and analyze target chart features in an image, the layout and reference values of a chart must be defined by a chart definition file. These files indicate the relative locations of features and important information about them for analysis, such as the expected color of a color patch area. They are dependent upon both the layout of features you want to analyze and the medium the chart is produced on. Below is an illustration of how this JSON-structured, plain-text file describes the features and their layout.

Arbitrary Chart Definitions

We encourage users to design their own chart layouts of combinations of the above features, as suits their needs. Currently, the generation of these designs is a manual process and there are no integrated tools for doing so.

Contact support@imatest.com if you need further assistance in producing a chart design. 

Once you have created your own chart design, both a graphic version and chart definition file, contact charts@imatest.com for precision fabrication of the design on a number of different substrate media. 

 

Note to Pilot Program members / Beta testers

The following limitations are present at the start of the beta testing period available to those in our Pilot Program which started August 11, 2017. These limitations apply to both Master and IT versions.

  • All module-operation options must be controlled via INI-field options, even for Imatest Master- there is no GUI-based options window for Arbitrary Charts at the moment.
  • Three-channel, color image data will be assumed to be sRGB only, no other color space. One channel data is analyzed as Intensity information- i.e. no allowances for color-filter-array information yet.
  • Input images in a batch run must be all the same type of data encoding (sRGB or Intensity).
  • Only the Random Direct analysis method is available on “Random Texture” features, even features marked with the appropriate RandomType as being “cross” features.
  • Alignment and auto-ROI-determination limitations: 
    • Only Automatic registration is supported, even in Imatest Master. In Imatest Master, users can be prompted to confirm and accept the alignment that was found, but cannot manually adjust it.
    • Only relatively low amounts of geometric distortion can be tolerated.
    • The chart must be oriented at least roughly correctly in the image, i.e. centered in the center of the image and with the upper left corner of the chart as it is implicitly defined by the chart definition file.

In addition to the above, features will continue to be added during the beta period, such as ini-file options for control of various aspects of the analysis.