Testing lenses: Introduction Lens quality (especially sharpness) has always been of great interest to photographers. It’s what we spend the big bucks for— if we have them. And it’s what we look for in a lens at any price point. Traditionally, lens testing has been highly tedious, best left to professionals and large publications. With Imatest, that has changed forever. All you need to do is photograph an SFRplus, ISO-12233:2014+ eSFR, or tilted checkerboard chart (with careful technique of course), run SFRplus or eSFR ISO, and interpret the results. This page contains the recommended procedure for testing lenses using Imatest […]

Analysis of random scale-invariant patterns, including the Spilled Coins (Dead Leaves) Pattern, for measuring texture sharpness   Random/Dead Leaves, which runs under the interactive Rescharts interface or as a fixed (non-interactive, batch-capable) module, measures SFR (Spatial Frequency Response) or MTF (Modulation Transfer Function) from random scale-invariant (or approximately scale-invariant) test charts, including “Dead Leaves” and “Spilled Coins” charts. It is primarily used to measure the effects of signal processing on image texture. Dead leaves/Spilled Coins charts are of increasing interest because their statistics resemble those of natural scenes; they are less affected by edge sharpening than other patterns (especially the […]

Analysis of log frequency-varying charts Introduction Log frequency, which uses the Rescharts interface, measures the contrast of narrow bar or sine charts that increase logarithmically in spatial frequency. It also measures color Moiré (Imatest Master only). When the image pattern is sinusoidal (rather than a bar chart), contrast is equivalent to SFR or MTF. This method is more direct than the slanted-edge method, but less accurate and more susceptible to noise. A chart can be created by Test Charts and printed on a high quality inkjet printer. Log Frequency image (complete and cropped) The image above used to illustrate the […]

Analysis of Log Frequency-Contrast charts New in Imatest 4.0  Automatic region is available with the revised version of the chart, which includes registration marks in the corners. Sharpness and Texture Analysis using Log F‑Contrast from Imaging-Resource compares the the effects of sharpening and noise reduction in several cameras using images downloaded from Imaging-Resource.com. Introduction Log F-Contrast (short for Log Frequency-Contrast; not in Imatest Studio) measures the effects of signal processing— noise reduction and sharpening— on imaging system performance using a chart that varies in spatial frequency on the horizontal axis (log frequency increases with x) and in modulation (i.e., contrast) […]

Measure visible sensor defects The Human Visual System – Algorithm – Instructions – Settings window – Filtering and threshold – Display options – Defective pixels – Tuning – Results Blemish Detect detects visible sensor defects (typically blurred (dark) spots caused by dust in front of the image sensor, but light blemishes can also be detected). To ensure that only visible blemishes are flagged— and blemishes below the threshold of visibility are not— the image is filtered by a response function derived from the Human Visual System (HVS). Filter settings are adjustable for a wide range of applications and viewing conditions. Blemish detect also includes all […]

Imatest 4.5  The Checkerboard Module, which calculates distortion, MTF, and lateral chromatic aberration is Imatest’s primary recommended means of calculating optical distortion. It produces highly accurate results and works well with highly barrel-distorted (fisheye) images, which cannot be analyzed with the Distortion module. SFRplus also measures distortion with similar results to the Distortion module. A key advantage of SFRplus is that it can measure distortion in highly barrel-distorted (fisheye) lenses using pre-distorted charts. It can also measure Field of View (in addition to performing a great many image quality measurements). Distortion is one of several Imatest modules that calculate optical distortion. These modules […]

Create test charts for high quality inkjet printers Although we strongly recommend that customers purchase charts from the Imatest Store, the Imatest Test Charts module allows you to create test chart files for printing on high quality photographic inkjet printers. If you plan to print charts using this module, you should be skilled at fine printing and have a knowledge of color management to obtain optimum chart quality; otherwise we recommend purchasing charts at the Imatest Store. Disclaimer: Although we sell most of the charts generated by the Imatest Test Charts module, several variations are not available because (A) it’s […]

Monitor patterns for Light Falloff, SFR, Distortion, and monitor calibration Introduction Screen Patterns displays a variety of test patterns on monitors, preferably on LCD flat screen monitors. It may become more useful as cost-effective ultra-high resolution (4k+) monitors become available. It is opened by clicking on Screen Patterns on the right of the Imatest main window. Most patterns (except perhaps Monitor calibration) perform best with the window maximized. You may need to redraw the pattern after maximizing (or resizing) it by selecting the pattern or changing one of the settings. These patterns are offered as a convenient alternative to the […]

How Imatest IT/EXE works Imatest IT/EXE (Industrial Testing EXE; formerly API/EXE) is a set of standalone programs initiated by DOS calls, which can be issued by a test system. The programs have the same functionality as the corresponding Imatest Master modules, but they operate without user intervention, making them suitable for use in automated testing systems. They are represented by the blue box in the lower right of the figure below. Imatest IT/EXE flow diagram The test system interacts with the IT/EXE programs through files specified in the DOS command line— primarily an image file and an INI control file […]

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. Suppliers Most test charts are available from the Imatest Store. Supplier Chart(s) and comments Location Imatest A large variety of charts (sharpness, color, tone, dynamic range) may be ordered from the Imatest store. Boulder, CO USA Stouffer The Stouffer T4110 transmission step wedge was recommended for single-image Dynamic Range measurements […]

Which version is right for you? Imatest 5.0:  All functions of Imatest Image Sensor have been incorporated into Imatest Master.   Imatest is available in several GUI (Graphic User Interface)-based versions. Studio, with everything individual photographers need to test their cameras and lenses. Studio is only available to individual photographers. Master, the full-featured industrial-strength version for engineers and scientists who develop and evaluate imaging systems. Acquire images directly from several manufacturer’s development systems. Images can be updated and analyzed in real time with the Rescharts, Multicharts, and Uniformity-Interactive modules. As of Imatest 5.0, Image Sensor (IS) has been discontinued. All […]

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 […]

Imatest SFR allows you to analyze and display several regions of interest (ROIs) in an image. Display options can be selected from three dropdown windows from the SFR settings window. Multi-ROI plots lets you choose the plot type: 1D or 2D; units in Cycles/Pxl, LW/PH (Line Widths per Picture Height), or LP/PH (Line Pairs per Picture Height).The 1D summary plots, which display results as a function of the distance from the image center, may be difficult to read for lenses that are poorly centered and hence have asymmetrical response. In most cases 2D summary plots are far more readable. 1D […]

A pattern on an LCD screen may be used for SFR measurements using a pattern generated by the Imatest Screen Patterns module, which has several patterns to choose from. These patterns are convenient, but somewhat limited in usefulness because an LCD screen can only cover a fraction of the image frame, hence you can’t produce a good map the camera’s MTF response. Screen Patterns The Screen Patterns module is opened by clicking on Screen Patterns on the right of the Imatest main window. When it first comes up, it is completely blank (for use with Light Falloff). Select SFR: Quadrants […]

From the Imatest main window, click on SFR or Rescharts on the upper left. SFR allows you to analyze multiple regions and to run batches of files. Rescharts (1. Slanted-edge SFR) allows you to analyze single regions in a highly-interactive interface. ISO 12233:2000 chart images, which have contrasty (≥40:1) slanted-edges, can be downloaded from dpreview.com reviews, typically in the last page titled “Compared to…,” and from Imaging-resource.com reviews, typically on the page labeled “sample images.” We no longer recommend such high contrast images, because saturation can lead to inaccurate results. 4:1 or 10:1 contrast images are much preferred. Image file […]

Setting up and photographing SFR test charts Imatest SFR measures spatial frequency response, also known as the Modulation Transfer Function (MTF), of digital cameras using a slanted-edge (light-to-dark) target, as described in Sharpness: What is it and how is it measured? Although it doesn’t provide the as strong a visual indication of MTF as wedge or sinusoidal chats (such as Log Frequency), it provides a more accurate quantitative measurement and uses space much more efficiently. Old ISO 12233:2000 test chart (left) with Imatest SFR cropping indicated by the red rectangle New ISO 12233:2014 test chart (right– supported with a high […]

Imatest software can measure a great many digital camera image quality factors from test chart images. If you’re just getting started we recommend that you explore the Image Quality factors page. The two most widely used modules, SFRplus and eSFR ISO, can measure a great many image quality factors from single test chart images. Other modules and charts let you work with a wide variety of testing challenges. Running Imatest – Three helpful buttons – RAW files – Misc. controls and utilities ROI Options – Options II – EXIF data – Dropdown menus – Figures – CSV & JSON output    Running Imatest Imatest […]

Photographic scientists and engineers stress the fact that no single number satisfactorily describes the ability of a photographic system to reproduce the small-scale attributes of the subject —Leslie Stroebel,John Compton, Ira Current, Richard Zakia Basic Photographic Materials and Processes, Second edition, p. 273 (Micro-image evaluation chapter), Focal Press, 2000 News: Imatest 2020.1 (to be released March 2020)  Shannon information capacity is now calculated from images of the Siemens star, with much better accuracy than the old slanted-edge measurements, which have been deprecated. Star measurements are the recommended method for calculating information capacity.  Prior to the 2020.1 release, you can obtain […]

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 typically uniform over the sensor and can be caused by physical misalignment of multi-chip sensors […]

Introduction – Examples – Oversharpening and Undersharpening – Examples  Unsharp masking (USM) – Links – Standardized sharpening   Introduction to sharpening Sharpening is an important part of digital image processing. It restores some of the sharpness lost in the lens and image sensor. Every digital image benefits from sharpening at some point in its workflow— in the camera, the RAW conversion software, and/or image editor. Sharpening has a bad name with some photographers because it’s overdone in some cameras (mostly low-end compacts and camera phones), resulting in ugly “halo” effects near edges. But it’s entirely beneficial when done properly. Almost every digital camera sharpens images to some degree. Some models […]