Imatest Glosario Par Pablo Ruiz Garcia Aliasing. Elementos de baja frecuencia, a veces muy molestos, que aparecen cuando la energía de la señal alcanza al sensor digital por encima de la frecuencia Nyquist. El efecto de flecos moire son un tipo de alilasing. Aberración cromática. Es una característica de la lente que provoca que las distintas longitudes de onda formen foco en distintos puntos. Existen dos tipos; longitudinal, donde los diferentes colores forman su foco en planos distintos. Y, lateral, donde la longitud focal de la lente, por lo tanto la ampliación, es diferente para cada color. La aberración cromática […]

Overview Why Imatest?     |     Test Charts     |     Lighting     |     Image Capture Technique     |     Setting up Your Lab     |     Using Imatest Software If you are getting started with Imatest — or need a good reference on using it — we recommend Imatest Instructions– Getting started. Why Imatest? Introduction Imatest charts and software allow you to measure the characteristics and quality of cameras and imaging systems. To begin measuring the resolution or color of your camera, you’ll need an image of a test chart. Imatest offers all-in-one test charts that can test […]

Gamma is the exponent of the equation that relates scene luminance with image pixel level. When the raw output of the image sensor, which is linear, is converted to image file pixels for a standard color space, the equation below is applied (very approximately, as we’ll explain below). pixel level = (RAW pixel level)gamma_camera ~= exposuregamma_camera      (1) When an image file is sent to a display (a monitor or print), Output luminance = (pixel level)gamma_display      (2) The total system gamma is gamma_camera * gamma_display.  Standard values of display gamma are 1.8 for older color spaces used in the Macintosh and 2.2 […]

Postprocessor for SFRplus, Checkerboard, and eSFR ISO for analyzing image quality factors that require multiple images: Curvature of field, Longitudinal (Axial) Chromatic Aberration, & more Introduction to FocusField FocusField is a postprocessor for displaying camera test results from batches of images acquired at different distances and/or with different focus settings (also with different apertures), then analyzed by SFRplus, Checkerboard, or eSFR ISO  batch runs. (These modules are preferred because magnification, and hence distance, can be derived from the image.) It can display Depth of Field (DoF), Curvature of field, Longitudinal (axial) chromatic aberration, and Lens focal length (when used with the motorized […]

Find the sharpest files in a batch Thanks for Andrea Nivini for suggesting this module. New in Imatest 5.2: A major redesign of Find Sharp Files. A summary plot is available. Results can be shown in an easy-to-read Table format. Results can be saved in CSV and JSON files.   Find Sharpest Files lets you quickly and conveniently rank the sharpness of a set of images. It works on any image— it doesn’t have to be a test chart. It runs much faster than any of the standardized sharpness measurements (slanted-edge, star, etc.). There are a number of situations where this capability […]

For more information on how to use INI files in Imatest IT, we recommend the Imatest INI File Reference For Imatest IT, most of these entries don’t need to be entered. Many don’t affect Imatest IT results: they control interactive figure displays or figure output formats (figures are often not used in Imatest IT). Background Meaning Yellow Yellow background: Important to Imatest IT. Parameter and Description are in boldface. [IT] Cyan Cyan background: Figure settings. (Figures are used infrequently for IT.) [f] Gray Gray background: For interactive operation. No effect on IT. Clear Clear background: Results details (units, scaling, etc.) […]

This page describes Imatest’s distortion calculations, comparing the different distortion formulas and modules. Distortion formulas – Modules – TV Distotion and Field of View – Image, Geometry, Distortion, FoV display Radial distortion plot – Distortion Contour plot – Compare results – Links Lens distortion has two basic forms, barrel and pincushion, as illustrated below. None Barrel Pincushion In addition to these three, there can be “mustache” or “wave” distortion, which is barrel near the center and pincushion near the edges, or vice-versa. Distortion formulas In the equations which apply to several modules, rd is the distorted (measured) radius normalized to the center-to-corner distance. […]

Imatest 4.5+   The Checkerboard Module is strongly recommended for distortion measurements because its corner detection algorithm is much more accurate and it is tolerant of large amounts of optical distortion, which can cause the Distortion module to fail. Checkerboard, which calculates distortion, MTF, and lateral chromatic aberration is Imatest’s primary recommended means of calculating optical distortion. The Distortion module will be removed after the 22.2 release and is not recommended for new work. If you are using it, we recommend avoiding the grid (line) pattern because it is much fussier than the checkerboard: thin lines may fail to be detected; thick lines reduce […]

Lens aberrations, diffraction, and defocus (or focus error) are basic factors that limit lens sharpness. They are described in the following sections. Lens aberrations – Diffraction – Pixel response limits and Q – Visualizing Q – Defocus  Lens (Optical) Aberrations Imperfections in optical systems arise from a number of causes that include different bending of light at different wavelengths, the inability of spherical surfaces (or even ashperes) to provide clear images over large fields of view, changes in focus for light rays that don’t pass through the center of the lens, and many more (i.e., coma, stigmatism, spherical aberration, and […]

In January 2013 Imatest released the Spilled Coins test chart, which is an improved version of the Dead Leaves chart for measuring a camera’s fine texture response. (It’s available in the Imatest Store in both monochrome and color versions.) Shortly afterwards, Jason Cope of our partner company Image Quality Labs found an anomalous result and called me to find out what was wrong. When I looked at the image I realized that he’d done the test correctly. He had found an image whose processing defeated the intent of the dead leaves chart, which is to accurately measure a camera’s texture […]

Tables to help you navigate Imatest modules and charts Imatest is a complex, rich application involving a great many image quality factors, modules, and test charts. The tables below, for Quality Factor, Module, and Test chart are designed to help navigate the site. A Table of contents is also available. Image quality factors – Modules – Test charts – Test images  Algorithms – Suppliers Image quality factors Image quality factors have their own page. A brief list of recommended test charts is given in the FAQ. Quality factor Charts Module Comments Camera, lens Color accuracy X-Rite ColorChecker (24-patch) Colorcheck, Color/Tone […]

Related pages Dynamic Range  a comprehensive introduction: strongly affected by flare light. Veiling glare (lens flare)  describes several measurement techniques, including the new Contrast Resolution method. Making Dynamic Range Measurements Robust Against Flare Light         Introduction – Background – The Contrast Resolution chart – Photographing & analyzing – Tonal response and SNR – Visualization – Visual analysis – Contrast Resolution Dynamic Range – Tone mapped results – Flare Mask & two-image measurement – Summary – Verification – References    Introduction This page describes the Imatest Contrast Resolution chart and analysis (supported by Imatest 5.0+), which is designed to measure […]

including raw (image sensor), chroma, and visual noise as well as several types of Dynamic Range calculation Related web pages Using Color/Tone Interactive (Multicharts) – Interactive analysis of color & grayscale test charts Using Color/Tone Auto – Fixed (batch-capable) analysis of color & grayscale test charts Dynamic Range – a general introduction with links to Imatest modules that calculate it. Noise in Photographic Images – a basic introduction Color Correction Matrix (CCM) Calculate a matrix (usually 3×3) for correcting image colors (often from RAW images)   Color/Tone Setup (formerly Multicharts: Imatest ‘s interactive module for measuring most well-known color and grayscale charts), Color/Tone Auto (formerly Multitest: the batch-capable […]

Introduction  |  Measurement  |  Modules  |  Demosaicing Purple fringing – CA correction for non-tangential edges Introduction Chromatic aberration (CA) is one of several aberrations that degrade lens performance. (Others include coma, astigmatism, spherical aberration, and curvature of field.) It occurs because the index of refraction of glass varies with the wavelength of light, i.e., glass bends different colors by different amounts. This phenomenon is called dispersion. It appears as color fringing, most visibly on tangential edges near the boundaries of the image. It is sometimes confused with another effect, which we call pixel shift— a color channel offset that is […]

Obtain and photograph chart –  Lighting – Distance – Exposure – Tips – Links Imatest Checkerboard performs highly automated measurements of sharpness (expressed as Spatial Frequency Response (SFR), Lateral Chromatic Aberration, and optical distortion from images of checkerboard patterns (with a recommended tilt angle of ~5-8 degrees for sharpness measurements). The primary advantages of Checkerboard are: Compared to Imatest’s other automatically-detected sharpness modules:  It is relatively insensitive to framing. You can zoom in or out as much as you like, as long as there are detectable corner features.  Compared to the Distortion (legacy) module:  It works with highly-distorted (fisheye lens) images. Calculations are more accurate, and it contains all results […]

For more information on how to use INI files in Imatest IT, we recommend the Imatest INI File Reference This document was created by running checkerboard in Imatest 5.2.0. ALPHA on 30-May-2019 22:57:20. For Imatest IT, most of these entries don’t need to be entered. Many don’t affect Imatest IT results: they control interactive figure displays or figure output formats (figures are often not used in Imatest IT). Background Meaning Yellow Yellow background: Important to Imatest IT. Parameter and Description are in boldface. [IT] Cyan Cyan background: Figure settings. (Figures are used infrequently for IT.) [f] Gray Gray background: For […]

Imatest 5.1 has important new capabilities for measuring and correcting MTF degradation caused by test charts. These new capabilities are far easier to understand and apply than CQI. Chart quality calculator Compensating camera MTF measurements for chart and sensor MTF As a result of the improved measurements, the Chart Quality Index measurement has been deprecated. The Chart Finder is an interactive web page that can help you select the appropriate chart size and media. It contains results from this page, but without the math. Summary In order to determine the suitability of a test chart is for measuring the performance of a […]

Imatest lets you use the measured test chart modulation transfer function (MTF) to Determine the suitability of a test chart, which is characterized by size (height), print media, and printing technology, for camera MTF measurements where the camera is characterized by the number of vertical pixels. This can help determine whether a test chart is appropriate for a specific application.  Increase the accuracy of MTF measurements by dividing the measured camera MTF by the chart MTF projected on the image sensor. This is equivalent to deconvolution in spatial domain. This technique is described in Compensating camera MTF measurements for chart and […]

Postprocessor for viewing summaries of SFR, SFRplus, Checkerboard, and eSFR ISO results Introduction to Batchview Batchview is a postprocessor for displaying lens test results generated by SFR, SFRplus, and eSFR ISO batch runs (analyses of groups of test chart images taken at various apertures, focal lengths, etc.). It can store and display up to four sets of results for convenient comparisons in Imatest Master; two in Studio. Postprocessor comparison Each lets you compare sharpness of different regions and/or images MTF Compare Postprocessor to SFR, SFRplus, and eSFR ISO. Input is two CSV results files for individual regions. Lets you compare individual […]

Imatest 4.4+ can evaluate auto-focus (AF) as a measure of MTF with respect to time. This can be performed by using the SFR module with an appropriate video file. Related pages Auto Exposure in Stepchart Autofocus Speed in SFR Auto White balance in Colorcheck Uses/Purpose This metric is intended to be used as a way to measure the time a camera system takes to auto-focus. Rise time and settling time are automatically calculated. This measurement does not provide information about the accuracy or precision of auto-focus. To evaluate those measures, several measurements should be performed on the final, settled images and compared. File […]