Color/Tone Interactive Analysis

Measure color accuracy, tonal response, and noise
from a large variety of test charts

Introduction – Getting started – Supported charts – Reference files – The Color/Tone Setup window
More settings – Dropdown menus – Displays and options

News– Imatest 5.2: Multicharts (the highly interactive module for measuring color accuracy, tonal response, and noise) has been renamed to Color/Tone Interactive, and Multitest (the fixed/batch-capable version of Multicharts) has been renamed to Color/Tone Auto. For now the old names will be used for INI file sections and some documentation. An INI File Monitor captures the contents of INI files (which can be used control Imatest IT runs), and displays them in a web browser table.  A Color Difference Visualizer app (separate from Multicharts) has been added so you can interactively examine the appearance of color differences. Imatest 5.1: (starting December 2018)  The exposure error calculation has been improved to be more consistent over a range of contrast (gamma) values. Details here.  Color/Tone Interactive and Auto can now measure temporal noise and SNR. With this enhancement, these two new modules have all major features of the older Stepchart and Colorcheck modules. Nonuniformity correction, available since Imatest 4.5, has been documented.

Supported charts (not all are shown below)

Select a chart to analyze by clicking on one of the entries in the Chart type popup menu described above or by clicking on Read image file if the correct Chart type is displayed. The Read image file button and popup menu (shown on the right) are highlighted (yellow background) when Color/Tone Interactive starts. Color/Tone Interactive and Auto support all charts shown and described below:
	The standard 24-patch X-Rite ColorChecker® Classic. ColorChecker charts (Classic and SG) are available in the Imatest store and from a great many suppliers worldwide. Images of both the 24-patch ColorChecker and SG can be found in Imaging-Resource.com camera reviews (in the samples section). Danny Pascale/Babelcolor’s page on the ColorChecker contains nearly everything you want to know about the chart.  Builds of Imatest 5.1 after May 2018 can read pre and post-2014 Colorchecker values from CGATS files posted on this page.
	The industry-standard IT8.7 chart. IT8.7 charts come in several formats (reflective and transmissive), available from Wolf Faust (in the USA from Digital Light & Color). A high-gamut version is available from Hugo Rodriguez (website in Spanish). Reflective IT8.7/2 charts are relatively inexpensive. IT8.7 charts are usually printed on photographic paper or film (consisting of three dye layers). They must be used with reference files, which are available from manufacturer’s websites. Ian Lyons has a nice description of IT8.7 charts.

	The 140-patch X-Rite Colorchecker SG (Imatest Master & IS-only), which has a semigloss (SG) surface. It contains a 6×4 patch area in the upper-middle that is similar to the 24-patch Colorchecker, except that the colors are more saturated. Available from the Imatest Store. Builds of Imatest 5.1 after May 2018 can read pre and post-2014 Colorchecker SG values from CGATS files posted on this page.
	Linear grayscale step charts (consisting of a single row of patches) such as the Kodak/Tiffen Q-13/Q-14 (inexpensive and widely available) or the Stouffer T4110 (Dmax = 4.0). Both reflection and transmission charts are supported. Charts with circular patterns (shown below) are preferred because they’re less susceptible to errors from lens light falloff (vignetting). Other stepcharts are discussed in Using Stepchart.
	Multi-row grayscale charts (Imatest Master-only): Several grayscale charts as well as 7-36 squares arranged on a circle, useful for analyzing pie or circular charts. Described on a separate page. Above: ISO-15739, ISO-14524. These charts are less susceptible to measurement errors from light falloff than linear charts. On left:  Imatest Standard Dynamic Range chart – 36 patches Contrast Resolution Chart– See Contrast detection probability (CDP)
	DSC Labs ChromaDuMonde 28/28R widely used in the cinema and broadcasting industries for calibrating cameras. Useful with the vectorscope display. Imatest Image Acquisition features auto-refresh for full vectorscope functionality.
	The Universal Test Target (crop shown on right) is primarily designed for testing scanners. Multicharts can analyze the 9×3 color pattern to the left of center (with the 9 light regions at the bottom) as well as the 20-step grayscale step charts (which have step increments of L* = 5). When the stepchart is analyzed (using 6. Stepchart (linear)), Ref (Reference file or data source) should be set to L* = 95:-5:5,1 (20-step UTT).
	General mxn charts (4×12 shown on the left). Any chart with an mxn grid can be analyzed. You must specify the grid size (click Settings, ISO 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.
	SpyderCHECKR (8×6) A small chart that competes with the Colorchecker. Should be oriented as shown. If you want to measure only half the chart (say, left or right), you’ll need to create a reference file with L*a*b* data available here.
	RezChecker and ColorGauge (nano and micro) charts from Image Science Associates, available in the Imatest Store. Professional grade miniaturized targets made in cooperation with Munsell Color Services from the same 18 pigments as the ColorChecker. Also has 12 unique spectrally neutral glossy or matte gray patches for measuring dynamic range, tones, and imaging noise. The RezChecker slanted-edges have exceptionally high quality.Suitable for close up and macro photography. The patches are mounted on aircraft-grade anodized aluminum and are set below the top surface to help protect from damage. Nano patch sizes are 1/8” x 1/8”; 11/16” x 13/16” x 0.060” thick overall. Micro patch sizes are 1/4” x 1/4”; 1 -3/8” x 1-5/8” x 0.060” thick overall.
ISA can provide NIST-traceable measurements for Rezchecker patches. These measurements are in a difficult-to-use XLS/CGATS file format. To use this data as an Imatest reference file, open the file in Google sheets (which can be done directly in Gmail) or in Excel. Select the 30 rows representing the patches and the 3 column representing LAB L, LAB A, and LAB B, and copy them into the clipboard. Past into a text editor and save the file (with txt or csv extension). This will work well as a reference file.
Other charts: SFRplus 20-patch color, SMPTE/Hale Color Bars (6 patches), Image Engineering TE226 (9×5), the 285-patch 285-patch CMP DT003, QPcard 202/203 . We occasionally add charts on customer request.

If the image is the same size and type as the previous image analyzed by Multicharts and if Automatic region detection has not been selected (available for a limited number of charts), you’ll be asked if you want to use the same ROI (region of interest).

ROI repeat dialog shown with IT8.7 chart

If the image is not the same size and type, or if you answer No, a coarse cropping box appears. The initial crop doesn’t have to be precise: you’ll have a chance to refine it shortly. The crop box can be enlarged or maximized to make the selection easier.

• For either of the ColorCheckers (24-patch or SG) or the QPcard, leave a margin around the sides slightly smaller than the spacing between patches.
• For grayscale step charts, select the entire chart (all patches), choosing boundaries that give even patch size. (The white patch on the Q-13 and Q-14 is larger than the rest.)
• For IT8.7 charts, select an area that includes the boundaries around the color chart and the entire grayscale (the red rectangle in the fine adjustment box below).

Special settings for linear grayscale charts

If you selected 6. Grayscale Stepchart (linear*) and clicked No, select new ROI(s) in the ROI repeat window (if it appears), the box shown on the right appears. Select the chart type (which specifies the density step) and the number of patches (between 6 and 41). Kodak/Tiffen Q-13/Q-14 charts have 20 patches; the Stouffer T4110 (a transmission chart with a density range of 4.0) has 41. For the Universal Test Chart (UTT) L* = 95:-5:5,1 (20-step UTT) and 20 patches should be selected. *Linear charts have a single row of patches.

Stepchart type (reflective/transmissive, density step)

If you selected 7. Special Grayscale & Color charts, the box shown on the right appears, allowing you to select the grayscale chart type, with additional settings available for several charts, such as OECF 20-patch circular (densities), Squares arranged in a circle (the number of squares), and General mxn (rows, columns). You can also select the type of region selection (manual, auto) for the 36-Patch Dynamic Range chart (also selectable in Imatest Options (ROIs…) on the Imatest main window. You can run the most recent Special Grayscale chart by selecting 3. … (last grayscale) (where … will be the name of the last grayscale chart analyzed). This can save time for repeated runs. To correctly analyze the 36-patch High Dynamic Range (HDR) chart you must enter the individually-measured reference file.

Multicharts Special Chart Selection

If

After you’ve made the rough crop, the fine adjustment box appears. The original crop is displayed as the red rectangle. The patch regions to be selected are the small cyan squares or rectangles. This dialog box can be enlarged or maximized to facilitate the adjustment. It offers numerous options.

Fine region selection shown for the IT8.7 chart

• The entire ROI can be moved ( ^ > v < , upper-left).
• The top, bottom, left, or right sides can be moved ( T^ Tv R> R< B^ Bv L> L< , middle-left).
• Corners can be moved individually (any of the 8 buttons in each of the four corners, middle-left).
• Pixel values for the four corners can be entered (X(tl), Y(br), …, where tl = top-left, br = bottom right, etc.). The origin is the upper-left. Be sure to press the Enter key after entering a value.
• You can choose between Fine and Coarse movement (1 or 5 pixels of movement per click).
• The display can be zoomed out or in.
• The display can be lightened to view the dark regions more clearly.
• For some charts (those with relatively large patches) a Fill factor (linear) slider in the gray area above the No, Try again button specifies the relative size of the squares. Its default value is 0.5. Smaller values can be used where lens distortion or pattern alignment makes alignment difficult.
• The distortion slider allows highly distorted images (barrel or pincushion) to be analyzed.

When you have completed the fine adjustment, click one of the buttons on the bottom of the window. If you click Yes, Continue , an additional dialog box may appear. For example, for the IT8.7 chart it will ask for the required reference file. Some of the entries in the input dialog boxes, like color space, can be changed later. If you click Yes, Continue in Express mode , it will go directly to the Multicharts window, using saved (most recent) values. For example, it saves the IT8.7 reference file name.

To save ROIs for use in future runs or to retrieve ROIs saved in past runs, follow the instructions in How to save and retrieve region selections. The ROIs are for the individual chart (Colorchecker, Contrast Resolution, etc.), not for Multicharts as a whole.

 

The Color/Tone Interactive window

After the image file has been entered, the most recent Chart view is displayed. The 2D a*b* view (ideal and input values on the CIELAB a*b*) is shown below.

2D a*b* display of IT8 chart (CMYKRGB primaries), showing ?C 2000 ellipses

The main display image is on the upper left. Color differences are summarized below this image, except when the Probe is turned on (available for the pseudocolor and split color displays). The various ?E* and ?C* values are described in in Wikipedia. A thumbnail image of the chart is shown on the upper right. Available options are described below. The remainder of the right side is the control area.

The Zoom/Rotate 3D/Data Cursor dropdown menu, just below the upper-right thumbnail, determines the action when you click on the image.

Zoom	Click on the image or select an area to zoom into. Double-click to zoom out.
Rotate 3D	Rotate 3D images by clicking and dragging the mouse. Zoom is activated for all other (2D) images.
Data Cursor	Display a data cursor (shown on the right) for several displays including 4. 2D a*b*, 5. xy Chromaticity, and 6. u’v’ Chromaticity. When you click on Reference or Camera symbols, you get  a Data cursor with patch information: RGB and L*a*b* values (different for the reference and camera) and several color difference metrics.

 

The dropdown menu to the right of the Zoom/Rotate 3D/Data Cursor menu controls the display of the thumbnail image on the upper-right. The first two selections use the actual image. The rest use synthesized (reference and camera) patches.

Input image- whole	Shows entire input image
Input image- crop	Shows the cropped input image (all patches)
Ideal/Input split > sRGB	shows a split view of the ideal/camera patch values mapped to sRGB, which is similar to typical monitor color spaces. This is the default (recommended) setting (shown on the right for the X-Rite ColorChecker).
Ideal/Input split patches	shows a split view of the ideal/camera patch values with no gamut mapping. Colors will not be accurate for large gamut color spaces
Input > sRGB monitor	displays the input image mapped from its native color space to sRGB, which is similar to typical monitor color spaces
Input patches	displays the input image with no gamut mapping. Colors will not be accurate for large gamut color spaces
Ideal > sRGB monitor	displays the ideal image mapped from its native color space to sRGB, which is similar to typical monitor color spaces
Ideal patches	displays the ideal image with no gamut mapping. Colors will not be accurate for large gamut color spaces

 

Image area

The pale blue box on the right is the image area. It includes the Read image file button (and Reload button for Imatest Image Acquisition-only), the Chart type dropdown menu (described above), entries for image properties, and color correction matrix functions .

Reload (Imatest Image Acquisition-only) reacquires the image from a device or video stream (depending on how the image was originally acquired) or reloads it from a file.

Color space allows the input file color space to be selected. This color space is also used as the target for calculating the Color Correction Matrix (CCM). The color space is automatically read into Multicharts from the EXIF data when ExifTool has been selected in Options II; otherwise it must be entered manually. Several color spaces are available. The first six are primarily for still images. Most of the rest are for video/cinema. See the Wikipedia RGB Color Space page and brucelindbloom.com for overviews.

sRGB	The default space of Windows and the Internet. Limited color gamut based on typical CRT phosphors. Gamma = 2.2 (approximately), White point = 6500K (D65).
Adobe RGB (1998)	Medium gamut, with stronger greens than sRGB. Often recommended for high quality printed output. Gamma = 2.2, White point = 6500K (D65).
Wide Gamut RGB	Extremely wide gamut with primaries on the spectral locus at 450, 525, and 700 microns. One of the color spaces supported by the Canon DPP RAW converter. 48-bit color files are recommended with wide gamut spaces: banding can be a problem with 24-bit color. Gamma = 2.2, White point = 5000K (D50).
ProPhoto RGB	Extremely wide gamut. Gamma = 1.8, White point = 5000K (D50).
Apple RGB	Small gamut. Used by Apple. Gamma = 1.8, White point = 6500K (D65).
ColorMatch RGB	Small gamut. Used by Apple. Gamma = 1.8, White point = 5000K (D50).
Rec. 709 Legal	HDTV color space. Gamut similar to sRGB. D65 White point. Allowable pixel levels 16-235
Rec. 709 Full	HDTV color space.  Allowable pixel levels 0-255
ACES	Academy Color Encoding System. Gamma = 1 (linear). Extremely wide gamut covers all visible colors with primaries outside the visible spectrum. D60 White point. File data stored as half-precision floating point (OpenEXR format).
Rec. 2020 Legal	UHDTV color space. Much larger gamut than Rec. 709. D65 White point. Allowable pixel levels 16-235
Rec. 2020 Full	UHDTV color space. Allowable pixel levels 0-255.
DCI-P3	Digital cinema projection color space. 25% wider gamut than sRGB, covering most reflective surface colors. Gamma = 2.6.
Display P3	Used in the iPhone 8. Same gamut as DCI-P3, but gamma is approximately 2.2 (same as sRGB). May be a part of the new Apple HEIF file format, intended to replace JPEG. This is new information (as of late 2017). Reliable information is hard to come by.

Danny Pascale’s A Review of RGB Color Spaces is recommended for readers interested in an in-depth explanation of color spaces.

Ref lets you select source for the reference (ideal) chart values, as described above. The dropdown menu contents depends on the chart type. For the 24-patch ColorChecker and the ColorChecker SG you can select either standard chart reference values or you can read in values from data files (Imatest Master and Image Sensor) in CSV or CGATS formats. Values for the two ColorCheckers have been supplied courtesy of X-Rite.

Correction matrix calculates the Color Correction Matrix (CCM). Prior to calculating the CCM you should make sure settings (linearization, etc.) are correct by clicking on Settings or clicking Settings (dropdown menu), Color matrix and other settings…  After Correction matrix has been pressed it changes to Matrix calculated, highlighted with a yellow background. The correction matrix cannot be recalculated until a property of the image (new image, color space, reference file, or color matrix setting) changes. The Display input (or Corrected) dropdown menu, immediately to its left, is enabled. More details on using the Color Correction Matrix can be found here.

Display selection menu and area

The Display selection dropdown menu allows you to select one of the following displays.

1. Pseudocolor color difference. Shows the difference between the ideal and input color patches using any of several metrics. The pseudocolor scale is shown adjacent to the image (below, right). Probe is available for this display. Not the most useful display
2. 3D color difference (with split colors).
3. Split colors: ideal/input. Shows the patches split so that the ideal and input values are displayed in the upper left and the lower right or each patch region, respectively. Probe is available for this display.
4. 2D a*b*.
   
5. xy chromaticity.
6. u’v’ chromaticity.
7. Black & White density.
8. 3D L*a*b*. Shown on the right. L*a*b* coordinates can be difficult to visualize when viewed from a single angle. It needs to be rotated to be useful.
9. EXIF data and Color matrix. Shows EXIF data if available and the color correction matrix if it has been calculated.
10. Vectorscope preview. 
11. Noise analysis (not for all charts). A huge variety of noise, Signal-to-Noise Ratio (SNR) and Dynamic Range results are available, including ISO 15729 and CPIQ (Camera Phone Image Quality) results. See Multicharts/Multitest/eSFR ISO noise measurements for more details. Not available for charts with tiny patches, like the IT8.7 and ColorChecker SG.
12. Display image.  Many options are available including display single channel, boosted colors, and lightened image.
13. Read – color-correct – Save image.  Can be used after CCM has been calculated to apply the Color Correction Matrix to any image. The corrected image can be saved.
14. 2D CbCr (from YCbCr). 
15. HS (Hue-Saturation) from HSV. 
16. HS (Hue-Sat) from HSL. 

The Display area, immediately below the Display selection box, contains display options. The contents, which depend on the display selection, are described below in the sections for the individual displays.

Save screen (shown on the right) saves a snapshot of the current display (the entire Multicharts screen) as a PNG file (a widely-used losslessly compressed format). It also allows you to immediately view the snapshot so it can be used a reference for comparing with other results.

File name and Directory at the top of the window set the location of the file to save.

When you check the Open window in an image viewer… box, the current screen will be opened either the system default viewer (if the box under Image viewer is blank) or a viewer/editor of your choice (if the box contains the path name to the viewer/editor). I recommend using Irfanview, which is fast, compact, free, and supports an amazing number of image file formats. Its normal location in English language installations is C:\Program Files\IrfanView\i_view32.exe.

Save data Saves the key data in CSV and XML formats. This includes the input R, G, and B values, the input and reference L*, a*, b* values, and several of the color difference metrics.

Help opens this web page in an HTML browser window.

Exit terminates Imatest Multicharts, but the Imatest main window is still available.

More settings

Clicking the Settings button that appears in the Display area (for many displays) or clicking Settings (dropdown menu on top), Color matrix and other settings… or ISO speed, noise, mxn chart… opens the window shown below.

Multicharts settings window

Color correction matrix	Settings for the CCM calculation are described in the Color Correction Matrix page
Incident Lux	Must be manually entered for ISO Sensitivity (Exposure Index) calculations. Aperture and Exposure (s) are normally obtained from EXIF data, but may be entered manually if the EXIF data is absent.
Noise	Settings are described in the Multicharts/Multitest/eSFR ISO Noise page.
Rows, columns for General mxn charts	Select number of rows and columns for general mxn (rectangular) charts. A reference file is required for this chart selection.
Saturation level	Three settings that affect Dynamic Range calculations are available: Standard file: 255 (or 65535…),  ITU-R Rec. 601 (BT.601): 235,  Maximum detected patch level (useful when 255 can’t be reached).
Pixel offset	Enter the pixel offset to subtract from the data. Pixel offsets are not uncommon: they cause a premature flattening of Density curves.
Nonuniformity correction	Allows you to correct for nonuniform illumination using a separate flat field image taken under identical conditions. Opens the Nonuniformity correction window described in Nonuniformity Correction in grayscale and color chart modules.
Image orientation	(Applies to next read) Select among Standard image orientation, Mirror (H-flip), Mirror (V-flip), Rotate 180 degrees.

Dropdown menus      File     Settings     Color ellipses     INI File Settings     Help  

The Dropdown menus at the top of the Multicharts window are used for a large variety of utilities and settings.

File	Read image file Same as Read image file button Save image file Save the current image. Read image from clipboard Read image from clipboard (from external program). May fail for large images. Save corrected image Save the corrected image (after the Color Correction Matrix has been calculated). Save screen, Save data Same as buttons on the lower-right. Save L*a*b* results as CSV reference Saves the CIELAB (L*a*b*) of the input file for use as a reference file. Can be used as a “gold standard” in manufacturing. Copy L*a*b* reference to clipboard Copies current L*a*b* values of the input file for use in external programs. Copy density reference to clipboard Copies the density reference (which may be the default or from a reference file) to the clipboard, where it can be examined in an external program. Copy Color Matrix to clipboard Copy CCM for use in external program. Explore image file folder Open Windows Explorer (or Mac equivalent) in the image file folder. View all EXIF data View EXIF data (metadata) for current file. May be called at any time. Pass/Fail Monitor Turn on the Pass/Fail Monitor, which operates in the background to record pass/fail results. Useful for testing P/F criteria for Imatest IT. Close Exit Multicharts.
Settings	Read Raw Setup Open Generalized Read Raw setup for binary raw files. Font size: Small, Normal, Large, X-Large, XXL Select Font size (Select a good match to figure size for your system.) ROI Options Open the ROI Options window. Automatic ROI detection can be set here. Options II Open the Options II window Color matrix and other settings…, ISO speed noise, mxn chart… Open the (More) settings window, shown above. Noise & Visual Noise settings Open Noise settings window, described in Multicharts/Multitest/eSFR ISO Noise . Reset screen Reset screen to its original size and position. Annotation box Check to clear the Display area so you can manually enter a text annotation. Auto Reload Turn on automatic (continuous) reload (Image Sensor-only). DPX read: Reverse RB Reverse R and B channels when reading DPX files (a video format).
Color ellipses	Select ellipse display for 2D a*b*, xy Chromaticity, u’v’ Chromaticity, Vectorscope, and CbCr plots. If selected, ellipses representing Just Noticeable Differences (JNDs) for several color difference equations are displayed. This is a unique feature in Imatest (at the time of introduction). Previously, only a few examples were available in texts. This is the first time the JND ellipses can be compared for real charts. MacAdam, Delta-C 94, Delta-C 2000, and Delta-C ab (plain Delta-C) ellipses are available. MacAdam ellipses are mostly of historical interest. Delta-C 2000 ellipses are the most accurate— the best representation of perceptual JNDs. Delta-C ab circles (geometrical distance on the a*b* plane) are the most familiar, but they are not very accurate. Ellipses are magnified for clear display. You can choose between two magnifications (4× or 2× for the ?C displays).  A Color Difference Visualizer (separate from Multicharts) lets you interactively examine the appearance of color differences.
INI File Settings	INI file utilities, described in INI File Utilities.
Help	Open online Help pages— instructions relevant to Multicharts.