Using Info DR, Part 2: Chart analysis

Imatest Info DR (Information-based Dynamic Range) refers to the Imatest module and test charts designed to measure C4 information capacity over a wide range of illumination — especially for low light. Part 1 describes the InfoDR charts and how to photograph them. This page, Part 2, describes how to analyze the InfoDR charts in Imatest Rescharts and Color/Tone (limited capabilities).  InfoDR Results shows C4 summary results for a number of cameras.

Part 1 – Introduction – C₄ Information Capacity – Info DR chart versions – Lighting – Measuring illumination
Photograph (framing) 

Part 2 – Open, Select, & Read – Setup window – Results – Information-related displays
Comparison with traditional DR – More settings – Auto mode – Color/Tone 

Related pages

Image Information Metrics — Introduction and overview of information capacity and related metrics, with links. Using Rescharts — Introduction to Rescharts — an interactive interface for resolution-related charts, all of which can also be run in fixed batch-capable versions. Using Rescharts slanted-edge modules Part 2 — Selecting files – Setup window – ROI selection & analysis – Edge ID files – More settings window  – Secondary readout – Settings area – Gamma – Gamma from chart contrast ratio – Auto mode window – Warnings – Clipping – Summary  Rescharts Slanted-edge results Part 3 – SFRplus edge results — Multi-ROI summary – Edge and MTF – Chromatic Aberration – Acutance/SQF – Histograms & noise – Image, Geometry, Distortion, FoV – 3D Plots – Lens style MTF plot – Edge roughness – Point Spread Function – Summary – CSV & JSON output Rescharts Slanted-edge results Part 4 – SFRplus other results (tones, color, distortion, etc.) — Tonal response and gamma – Image, Geometry, Distortion, FoV – Radial distortion – Summary and EXIF data – Color analysis – Detailed noise plot – Summary – Links

These instructions are for the InfoDR module, which can run in interactive (Setup) mode or batch-capable Auto mode. In the the descriptions of the Setup and More settings windows, we focus on settings unique to Info DR. Settings that apply to other Rescharts modules are described in full detail in Using Rescharts slanted-edge modules Part 2.

We begin with instructions for Rescharts (interactive; Setup) mode, which allows you to enter and modify settings and to explore results. The settings are saved for Auto Mode runs, described below, which allow batches of files to be analyzed. 

Open Info DR, select the chart type, and read the image file

Normally, Auto ROI detection should be set. It can be found and set in the Dynamic Range … Info DR setting of ROI Options. 

Rescharts Chart configuration
dropdown menu

Rescharts analyzes several versions of Info DR chart, but doesn’t automatically detect them. To see which chart type has been selected, open Rescharts. The specific Info DR chart type is shown in the Chart configuration dropdown menu, shown on the right. If needed, you can select the correct setting (InfoDR: 3. Trans. LVT 2-layer 92 dB for this example). The setting will be saved. If you know you have the correct setting, you can skip this step. The chart configuration can also be entered in the More settings window.

Select 12. Info DR in the Chart area on the right to read the image file.

If the correct Info DR chart type has been saved, open Info DR to read the image file. Details may differ in the newer and traditional interfaces.

If automatic detection fails, manually set the ROIs by selecting the registration marks and refining the selection.

The InfoDR setup window opens.

Info DR setup window

InfoDR setup window

[We will fix some settings that are not quite right.  Changes: {Step chart — to be removed)  (Wedge — needs more testing)
(Analyze color pattern above — may be removed. Color pattern will be analyzed if a CIELAB (L*a*b*) reference file is used.
Image underexposed will be removed for Info DR because the active pattern is restricted to the center of the image.
(The area might be shrunk.)]

InfoDR setup window (Many settings shared with other modules are in 
Using Rescharts slanted-edge modules, Part 2 )

Setting	Description & recommendation
Settings area on the left (settings are duplicated in More settings.)	Used to select the channel for analysis and the linearization method. Typical settings: Y-luminance channel, Gamma selected from chart. Required setting: Chart contrast = 4. See Setup window in Using Rescharts Slanted-edge Modules, Part 2. (The linearization selecting may need to be adjusted to work better with the dark, fogged, and noisy images.)

Click  OK  to continue with the calculation.

Results

Numerous displays. selected by the dropdown menu just below Display on the right, are available, and many of them have options. The table below is a reference, with links to detailed descriptions. Information displays, highlighted in yellow, are described on this page. All others are on linked pages.

Display setting

1.  Edge and SFR (MTF)	Mean edge (top) and SFR (MTF) plot (bottom). Frequently used.
2.  Chromatic Aberration	Lateral chromatic Aberration: strongest near edges. Limited value for Info Dr.
3.  Acutance / SQF	Visual impression of sharpness. Full description here.
4.  Multi-ROI summary	Selected results for multiple ROIs.
5.  Tonal Response, Gamma/white Bal	Tonal response and gamma. Learn more about gamma here.
6.  Histogram and noise stats	Histogram and edge noise statistics. Rarely used. Speedup must be off.
7.  Summary and EXIF data
8.  Image & Geometry	Image, Geometry, Distortion, Field of View. May show ROIs.
9.  a*b* Color error
10. Split colors: Reference/Input
11. 3D & contour plots	3D and contour plots of selected variable (there is a large choice).
12. Edge roughness	Edge roughness (not a very good quality indicator; better for blurred images)
13. Noise, SNR, Dyn Rng	Noise, SNR, Dynamic Range. A great many options available.
14. Wedge MTF & aliasing
15. Wedge moiré
16. Multi-Wedge summary
17. Edge & Info Capacity noise	Mean edge (top) and spatially-varying noise (bottom; for information capacity)
18. Info-related: NPS, NEQ, SNRI…	Two plots with a large selection of results (standard and information metrics) for both plots.
19. Info metrics (C_4…) vs. exposure	Information metrics — most importantly C4 — as a function of exposure. KEY RESULT OF InfoDR.

Information-related displays

Note that More Settings can be called at anytime during interactive analysis, before or after calling displays (which might be affected by the settings).

Displays are shown in the Display dropdown menu on the center- right. For InfoDR, the available information-related displays are

1.   Edge and SFR (MTF)	Displays Info capacity in Edge plot on top; standard MTF/SFR plot on bottom.
17. Edge & Info Capacity noise	Displays Info capacity in Edge plot on top; spatially-dependent noise on bottom.
18. Info-related: NPS, NEQ, SNRi…	Displays two plots, each with a large selection of results.
19. Info metrics (C_4…) vs exposure	Displays several results (most importantly information capacity C4) as a function of illumination.

1.   Edge and SFR (MTF) 17. Edge & Info Capacity noise Since the Edge and SFR (MTF) plot (1) is highly familiar — it has been a part of Imatest since the very beginning — only the Edge & Info Capacity noise plot is shown. These plots are available for all slanted-edge modules. The upper (Edge) plot shows the C4 and Cmax information capacities measured the 4:1 contrast edge.  the lower plot shows the spatially-dependent noise. A peak near the edge indicates bilateral (nonuniform) filtering, common in JPEG files from cameras. Several statistics (mean signal and noise on either side of the edge) are displayed.
18. Info-related: NPS, NEQ, SNRi…  Image information metrics (NPS, NEQ, SNRi, and more) as well as several traditional metrics (MTF, LSF, …) are displayed in the Information-related: NEQ, SNRi, … display. A key feature of the Information-related… plot is that it displays two results: one at the top and one at the bottom, making it easy to compare and correlate different results. This feature has been used extensively during the development of the new metrics. The Log x-axis checkbox between the two dropdown menus (shown inside a red oval on the right) lets you select a linear or logarithmic x-axis for frequency plots, where appropriate. A large selection of results is available in the Information-related… dropdown menus for the upper and lower plots, shown inside the red ovals in the Rescharts  Display  area, above right. The Information-related… dropdown menu is something of a monster. It contains more entries than ideal (you have to scroll to see them all; not all are shown on the right). More plot examples are shown in Image information metrics from Slanted edges: Instructions — Results
Line Spread function (LSF; upper plot), Square visibility (lower plot)	Noise Equivalent Quanta (NEQ; upper plot),  SNRi (lower plot)
List of plots for Info related: NPS, NEQ, SNRi, … display Upper and Lower plots Notation is from the EI2024 paper.  Noise Amplitude Spectrum NPS(f) Also called the Wiener spectrum. An important intermediate result used to calculate the Kernel, \(K(f) = SFR^2(f)/NPS(f)\) and other key metrics. Noise Power Spectrum (NPS)  \(N_V(f) = \sqrt{NPS(f)}\) Noise Equiv. Quanta (NEQ) A frequency-dependent SNR power that represents the number of quanta incident on a pixel for photon-dominated signals. \(NEQ(f) = \mu^2\ K(f)\) SFR (MTF) Spatial Frequency Response (synonymous with Modulation Transfer Function). Key measure of sharpness.  Edge linearized unnormalized μS(x) The average edge (the output of the ISO binning algorithm) Line Spread Function (LSF) \(LSF(x) = d \mu_S(s)(x) / dx\)  The derivative of the edge Edge noise amplitude \(\sigma_S(x) = \sqrt{N(x)}\) Noise autocorrelation IFFT(NEQ(f)) An experimental measurement related to sensor crosstalk. SNRi square w x w Ideal Observer SNR for square objects (with w × w pixel sides).  SNRi rectangle w x 4w Ideal Observer SNR for rectangular objects (with w × 4w pixel sides).  SNRi square per pixel^2 SNRi per pixel2 for a w×w square. Levels off; doesn’t increase indefinitely. SNRi rectangle per pixel^2 SNRi per pixel2 for a w×4w rectangle. Levels off; doesn’t increase indefinitely. LSF Doublet shift  Line Spread Function doublet shift as a function of spacing LSF Doublet amplitude  Line Spread Function amplitude as a function of spacing LSF doublet S/N energy  Line Spread Function energy as a function of spacing Edge Location sigma sq. w x w  Edge location standard deviation for a for a w×w square. Edge Location sigma rect. w x 4w  Edge location standard deviation for a for a w×4w rectangle. Edge SNRi 1D doublet  Edge SNRi for a for a long 1D object. Object matched filter Fmatched-object(f) Response of matched filter that optimizes SNRi Edge Location matched filter  Fmatched-edge(f) = f × Fmatched-object(f)  Response of matched filter that optimizes Edge SNRi   Lower plot-only  Original image crop The original (input) ROI Unbinned image crop Reverse-projected; low noise Noise image crop Original image – Noise image, lightened and contrast-boosted for display. Results summary Text showing C4 and Cmax from the Edge variance and Noise image methods, as well as other results, some of which are experimental and may change. Square visibility image A synthetic image showing the visibility of squares of various sizes (1×1 to 14×14 pixels) and Michelson contrasts (0.6 for 4:1 chart contrast, 0.3, and 015). The LARGE version covers both the lower and upper display areas. Square visibility – LARGE More plot details can be found in Image information metrics from Slanted edges: Instructions — Results 19. Info metrics (C_4…) vs exposure This plot is only available with Info DR.
The upper plot displays the selected variable, from the list below. Info Capacity C_4 Info Capacity C_max SNRi (nx4n pixels) Edge Location signa (nx4n pixels) Gamma (from edge) Mean ROI level Edge contrast ratio MTF50 MTF50P MTF Area Peak Norml MTF20 (Secondary readout 1) (Secondary readout 2) The x-axis can be set to  Log_10 exposure (-Optical Density  (-OD)),  Exposure dB,  F-stops (EV),  Patch number, Luminance cd/m^2,  Sensor Exposure H in Lux-Seconds, or log10(Sensor Exposure H in Lux-Seconds). The first three are relative units based on logarithms: OD (log10), dB (20×log10), and EV (log2). The last two are absolute units, based on illuminance or luminance measurements described in Part 1 of the InfoDR instructions. The last two entries, for Sensor exposure H (the total illumination reaching the sensor in Lux-seconds), are derived from an approximation in ISO 12233:2006, Annex B.	The primary result of interest is the information capacity for a 4:1 contrast edge or object, C4 (or C_4). The others are of secondary interest. MTF values ordinarily don’t vary much with exposure (though they can be affected by image processing). The lower plot displays the density response (log10(signal)).  Edge information capacity C4 for compact camera with 2.14 um pixels Information capacity can have units of Bits/pixel  (preferred most of the time) Megabits/mm2  (pixel pitch must be entered) Megabits/image

Exposure in Lux-seconds = Ha= 0.65 La t/A2              where a denotes the arithmetic mean (ISO 12232 nomenclature).  H is traditionally displayed logarithmically (as log10) in film characteristic curves, such as the one shown on the right for Fujichrome Provia 100F color reversal (slide) film. The film plot is the horizontal mirror (i.e., the upside-down version) of the lower log10(DN/DNmax) plot for the LX7 (shown above). The plot of Edge Information Capacity C4, Dynamic Range, and summary metrics, is repeated on the right. Dynamic Range is summarized on the upper-left and shown as the colored bars on the lower-right. The thresholds for DR quality levels in the above plot (C4 = 2, 1, 0.5, 0.2, and 0.1 for Excellent, High, Medium, Low, and Bad) are preliminary, based on a limited sample of images. They are likely to change after further study. We looked at results all the patches with Edge & Info Capacity noise plots with Show Large ROI & noise selected. The result shown below is marginal— for patch 17, just before edge detection fails. The plots are lightened for visibility.  An additional summary metric (with two different units) are shown on the left. C4 (total) is an experimental result, equal to the area (integral) under the mean of the C4 curve, using ΔDensity from the x-axis. This metric appears to correlate well with overall camera performance, but it needs to be verified. The two C4 (total) units are bits/pixel (for the quality of the individual bits) and Mb-total (for the quality of the image as a whole). They appear to correlate well with image appearance is several cameras we’ve tested, but we need to be sure the units and scaling are valid.

Comparison with traditional dynamic range

Information based DR can easily be compared with traditional SNR & slope-based DR by setting Display to 13. Noise, SNR, Dyn Rng and selecting 15. Scene-ref SNR DB & DR. The result is identical to running Color/Tone, described below. Dynamic Range measurements are generally lower than the C₄ DR Information-based measurements (above), partly because the damaging effects of stray light are handled better.

More settings window

The More settings window can be called from the InfoDR Setup window at the beginning of an analysis or from the Rescharts window at any time.

Note that some of the settings in More settings are duplicated in the Setup window.

InfoDR More settings window. Many of the settings are shared with other modules and
described in Using Rescharts slanted-edge modules, Part 2 )

Settings specific to InfoDR

Setting	Description & recommendation
Chart contrast	Always 4 for InfoDR
InfoDR chart configuration	Recommended: this setting is normally kept. You can also select Vertical or Horizontal edges only. This setting is normally kept.
Information capacity – Auto edge noise detect	Select the correct chart configuration from one of the first four (the others are not available): 1. Reflective open ctr, 2. Transmissive open ctr, 3. Trans LVT 2-layer 92 dB (used in the examples on this page), 4. Trans VisNIR 2-layer 138 dB.
Color space	Detected automatically (can be changed). Adobe RGB was selected during the LibRaw conversion.
Grayscale/color reference	Select the appropriate reference file. Only density CSV files are available for the 2-layer transmissive charts.
Illuminance or Luminance	Make a selection based on the illumination measurement technique (previous page).
Information calculation	Info cap – Auto edge noise detect usually works best, but the other settings (mean or smoothed peak noise) can be used if appropriate. The information capacity calculation must be turned on.

 
Recommendations for other settings — available for most modules
Details in Using Rescharts SFR modules, Part 2

Speedup	Checked. Speeds up runs by removing some rarely-used calculations, like histograms, that are rarely useful.
Linearization method: Gamma calculated from chart contrast	Generally recommended. Other methods described in
Slanted edge calculation (lower-left)	Imatest 22.1 (recommended – defaut). Other settings may not give reliable calculations.

Click  OK  to continue with the calculation.

Auto mode

InfoDR Auto runs automatically, without additional input, after the input file (or files for batch mode) are selected. It uses settings saved from Rescharts interactive mode.

The Auto mode settings window can be opened from Rescharts interactive mode from the Settings area on the left side of the Setup window or the wide  Switch to InfoDR Auto mode setup  button at the bottom of the More settings window.

For normal operation, we don’t recommend any of the Single-region plots. There are simply too many of them to be useful. (They’re of more interest when running Rescharts interactive mode.) The primary plot of interest is Information metrics (C_4, etc.) vs. exposure. All others are optional, and most are better suited for eSFR ISO, etc.

InfoDR Auto mode settings

Color/Tone

InfoDR charts can also be analyzed from Color/Tone (Interactive or Auto), where they behave like standard dynamic range charts. Color/Tone cannot measure information metrics (C4, etc.). Info DR is selected from the Color/Tone window as shown near-right. The chart type can be selected from the lower-left corner of Color/Tone settings window, shown far-right and also from the Options II window.