Measure color accuracy, tonal response, and noise
from a large variety of test charts
|News– Imatest 4.2: Color difference ellipses (MacAdam, ΔC 94, ΔC 2000, and ΔC ab) can be displayed in several displays: a*b*, xy, u’v’, vectorscope, and CrCb.
Imatest 4.0: Automatic region detection is available for the Colorchecker and 36-patch Dynamic Range charts, set using the Options I: ROIs… button at the bottom of the Imatest main window or the Multitest settings window.
Imatest 3.10: The new Multitest module performs a non-interactive (fixed) analysis of all test charts supported by Multicharts, i.e., image files can be analyzed in batches. It incorporates nearly all the functionality of Colorcheck.
Imatest™ Multicharts analyzes images of nearly all popular test charts for color accuracy, tonal response, noise, and ISO sensitivity using a highly interactive user interface. It can be used to measure white balance and color response for a wide range of lighting conditions and scenes. It can also display the tonal response of monochrome charts (or monochrome portions of color charts). A color correction matrix can be calculated (not in Imatest Studio) and used to correct images. The Multitest module performs the same analyses using a non-interactive (fixed; batch-capable) interface.
Several of the supported test charts are shown below. The ChromaDuMonde, grayscale stepcharts, Universal Test Target (UTT), and several additional Special Charts are not supported by Imatest Studio.
(Micro, Nano, etc.)
Many other charts are supported, including SFRplus and eSFR ISO color patterns
(not automatically detected with run in Multicharts or Multitest),
SMPTE/Hale Color Bars (6 patches), TE226 (9×5) color and TE269 36-patch OECF chart.
Photograph the chart, using even glare-free lighting. The image does not have to fill the frame.
Open Multicharts. Select the chart type or (if the type is correct) press Read image file. There are some special chart types.
Select the image file to read.
For grayscale charts (selections 6 or 7) you’ll be asked to select the chart type. You can also enter the reference file.
Follow instructions for region selection. You may need to make a coarse region selection followed by a fine selection.
Select the Display. Because Multicharts is highly interactive you can change the Color space, reference file and other settings. You can calculate a Color Correction Matrix (CCM).
Many saved settings are shared with Multitest.
Photograph or scan the chart, taking care to illuminate the chart evenly (±5%) and to avoid glare, which can be problematic in charts with semigloss (SG) or glossy surfaces such as the reflective IT8.7 and ColorChecker SG. Glare can be especially difficult to control with wide angle lenses. To minimize the effects of light falloff in lenses, the chart should typically not fill the image field (especially for high-resolution images).
A low-cost lighting setup is described here. For testing white balance, you can photograph the chart in a scene under a variety of lighting conditions. The ColorChecker Passport Photo is especially suitable for this purpose. Some rectangular charts may be rotated by multiples of ±90° if they are geometrically symmetrical (these include the ColorCheckers (Classic 24-patch and SG), QPCard 01, and the Kodak/Tiffen Q-13/Q-14, but not the IT8.7 (where top and bottom are different).
To start Multicharts, run Imatest, then click the button. The Multicharts window will appear with brief instructions, which may be more up-to-date than the one shown below.
Multicharts opening window with brief instructions
Select a chart to analyze by clicking on one of the entries in the Chart type popup menu or by clicking on Multicharts starts. Three setting for grayscale charts, 3., 6., and 7., may require additional input, described below. (This list may not be complete; additional charts are added from time to time.)if the correct Chart type is displayed. The button and popup menu (shown on the right) are highlighted (yellow background) when
Multicharts and Multitest support all charts shown on the right and described below:
| 19. eSFR ISO 16-patch color
Select a chart to read.
|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.|
|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.
|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.|
|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 discontinued Mini ColorChecker, but smaller. Also has 12 unique spectrally neutral gloss gray patches for measuring dynamic range, tones, and imaging noise. 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.
|The 285-patch CMP (Christophe Metairie Photographie) DigitaL TargeT 003 (CMP DT003), which comes with an individually calibrated reference file containing XYZ and L*a*b* data. It can be used to generate extremely precise camera profiles.|
|The inexpensive 35-patch QPcard 202/203, which can be used with free downloadable software for profiling cameras. The QPcard should be photographed in landscape mode with the Qpcard logo on the right.|
|Other charts: SFRplus 20-patch color, SMPTE/Hale Color Bars (6 patches), Image Engineering TE226 (9×5). We occasionally add charts on customer request.
A standard Windows dialog appears with the chart type indicated in the title. Open the image file.
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 specifying grayscale chart type
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
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 ( , upper-left).
- The top, bottom, left, or right sides can be moved ( , 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 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 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 Multicharts window, using saved (most recent) values. For example, it saves the IT8.7 reference file name., 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 , it will go directly to the
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.
Most charts allow reference files to be entered using the Ref. dropdown menu in the image area on the right of the Multicharts window, below the Color space box. (IT8.7 and CMP DT003 charts require them.) The available settings depends on the chart type. The previous file is generally available in the dropdown list. Here is a summary of the available reference sources.
|Chart||Default values||Options (data from files)|
|Default values from GMB, BabelColor, or Danes Picta (a chart with the same geometry but different colors)||L*a*b*, xyY D50, or xyY D65 files in CSV format.|
|IT8.7||Requires a reference file in IT8.7 format, available from the chart manufacturer, generally available on their websites.||—|
|CMP DigitaL TargeT 003||Individually measured reference files are supplied with each target.||—|
|X-Rite ColorChecker SG||Default values from GMB (L*a*b* D50); See Note below||L*a*b*, xyY D50, or xyY D65 files in CSV format.|
|Stepchart (linear)||Even density steps of 0.1, 0.15, 0.20, or 0.30. For the UTT only, L* = 95 to 5 in steps of -5 for the first 19 steps and 1 for step 20. (20-step UTT) should be selected.||an ASCII density reference file with one density value per line can be entered.|
|Note: Several of the default reference values are derived from L*a*b* D50 values, i.e., L*a*b* values acquired under D50 illumination. When the color space has a different reference temperature (sRGB and Adobe RGB both have D65) a Bradford transformation is applied, resulting in a small change in the L*a*b* values. This is rarely a significant concern if you’re making images under a different illuminant: if the white balance algorithm is working properly, it should transform image colors to the appropriate values for the color space.|
Except for the IT8.7 and CMP DT 003, reference files must be in CSV (comma-separated) or CGATS format. CSV files can be opened and edited in Excel. Color CSV files (L*a*b*, xyY D50, and xyY D65) have three entries per line; density files have have one entry per line.
Here is an example of an L*a*b* CSV file.
CSV format (comma-separated variables).
Added spaces are for visual clarity (readability)-only.
|55.261, -38.342, 31.37
28.778, 14.179, -50.297
65.711, 18.13, 17.81
51.038, -28.631, -28.638
51.935, 49.986, -14.574
81.733, 4.039, 79.819
42.101, 53.378, 28.19
If you have a spectrophotometer you can create a custom reference file (in the CGATS format, supported by Imatest 3.10+) using techniques described in Measuring test chart patches.
The Multicharts 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 ΔC 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 ΔE* and ΔC* 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|
The pale blue box on the right is the image area. It includes the Chart type dropdown menu (described above), entries for image properties, and color correction matrix functions .button (and button for Imatest Image Acquisition-only), the
(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: the color space is not automatically read into Multicharts; it must be entered manually. Several color spaces are available. The first six are primarily for still images. The remainder 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. Fairly wide gamut, covering most reflective surface colors.
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.
Color Correction Matrix (CCM) (Imatest Master and Image Sensor-only). Prior to calculating the CCM you should make sure settings (linearization, etc.) are correct by clicking on or clicking Settings (dropdown menu), Color matrix and other settings… After has been pressed it changes to , 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.calculates the
Display selection menu and area
The Display selection dropdown menu allows you to select one of the following displays.
- 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
- 3D color difference (with split colors).
- 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.
- 2D a*b*.
- xy chromaticity.
- u’v’ chromaticity.
- Black & White density.
- 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.
- EXIF data and Color matrix. Shows EXIF data if available and the color correction matrix if it has been calculated.
- Vectorscope preview.
- 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.
- Display image. Many options are available including display single channel, boosted colors, and lightened image.
- 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.
- 2D CbCr (from YCbCr).
- HS (Hue-Saturation) from HSV.
- 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.
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.(shown on the right) saves a snapshot of the current display (the entire
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.
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.
opens this web page in an HTML browser window.
Imatest Multicharts, but the Imatest main window is still available.terminates
Clicking thebutton 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.
|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.|
|Pixel offset||Enter the pixel offset to subtract from the data. Pixel offsets are not uncommon: they cause a premature flattening of Density curves.|
|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.
|INI File Settings||INI file utilities, described in INI File Utilities.|
|Help||Open online Help pages— instructions relevant to Multicharts.|
Displays and options
1. Pseudocolor Color difference
Shows the difference between the ideal and input color patches using any of several metrics using a pseudocolor color map. If a color correction matrix has been calculated, the difference between the ideal and corrected patches are shown at the bottom. The pseudocolor scale is shown adjacent to the image.
color difference metrics. (Corrected colors are used if a color correction matrix has been calculated and Display corrected has been selected.) (Checkbox; Pseudocolor and Split views) turns on the probe, illustrated below. When the probe is on, you can probe any patch by clicking on it. The probe data (for the individual patch), shown below the split display, includes a small image of the ideal and input patch colors, ideal and input RGB and L*a*b* values, and several ΔE* and ΔC* The probe is turned off by clicking outside either of the images.
ΔE*ab, the geometric distance in L*a*b* space, is the most familiar, but ΔE*94, which is lower for chroma differences in highly chromatic colors (with large a*2 + b*2), is a better measure of visual color difference. ΔE*00 is the most accurate metric (based on an exceedingly complex designed-by-committee equation). More detail on color difference equations can be found here and in Wikipedia.
Pseudocolor display for IT8.7
Split display for IT8.7 illustrating Probe (available for pseudocolor and split color displays)
(Popup menu to the right of the Probe checkbox; also in 3D Color difference) Contains a list of color metrics (mostly difference metrics) including ΔE*ab, ΔC*ab, ΔE*94, ΔC*94, ΔE00, ΔC00, ΔL*, ΔChroma, Δ|Hue distance| , Δ(Hue angle) , Chroma (input) and Chroma (output).
Numbers (checkbox) displays numbers in the middle of patches if checked.
Color map (Popup menu) allows you to select the color map. The WYRMBK color map shown goes from White – Yellow – Red – Magenta – Blue – Black.
Uses the height of the patches to display the difference between the ideal and input colors. Any of several metrics (ΔE*ab, ΔC*ab, ΔE*94, ΔC*94, ΔE*CMC, ΔC*CMC, ΔE*00, ΔC*00, ΔL*, ΔChroma, Δ|Hue distance|, ΔHue angle, Chroma (input), Chroma (output)) can be chosen. The faces show split colors: reference (upper-left)/input (lower-right). This allows you to compare visual color differences with standard color difference metrics. Can be zoomed and rotated.
You can use this display to correlate ΔE and ΔC metrics with visual color differences. None of the metrics are perfect! The visual difference between the reference and input is often lower than the indicated differences because the color space and monitor gamuts (often sRGB) may be lower than the original chart gamut, especially for cyan and blue.
(Toggle button; short for Auto rotate) starts rotating the image. Rotation is quite slow; it may be less useful than the 3D L*a*b* plot (below). The image continues to rotate until the next time you press the button. It’s best to turn off rotation before switching to other views.
Light (Checkbox) Illuminates the figure to make the sides darker. Checked (On) recommended.
Color difference type (Popup menu) Described above under Pseudocolor display.
Background lightness (Slider) sets the background gray level.
Invert (Checkbox) inverts the up-down orientation of the 3D plot.
3D Color difference display for Colorchecker
3. Split colors
Displays a synthesized chart image with each patch split so the ideal value is in the upper left and the input (measured) value is in the lower right. If a color correction matrix has been calculated, corrected colors are shown at the bottom.
above under Pseudocolor display. (Checkbox) is the only option. Described
Numbers (checkbox) displays numbers in the middle of patches if checked.
Split Color display for IT8.7
4. 2D a*b*
Displays patch values on the CIELAB a*b* plane. Ideal values are displayed as squares; Input values are displayed as circles.
Expand (Checkbox; 2D a*b*, xy chromaticity, u’v’ chromaticity, and 3D L*a*b*) Zoom in so the data fills the image.
(Popup menu in the lower right of the Display area; also in xy chromaticity, u’v’ chromaticity, and 3D L*a*b*) selects the region of the chart to display. For the IT8.7 and ColorChecker SG charts only. Avoids clutter from the large number of patches in these charts.
2D a*b* display for IT8.7
5. xy and 6. u’v’ Chromaticity
Displays the xy and u’v’ Chromaticity diagrams, which separate the visible and invisible color values into colored and gray regions. Ideal values are displayed as squares; Input values are displayed as circles. The u’v’ Chromaticity diagram, which is more perceptually uniform than the more familiar xy diagram (shown in the Tour) is illustrated on the right.
(Checkbox) Turns the wavelength display (400-700 microns) on the periphery of the locus of visible colors on or off.
(Popup menu to the right of Wavelth) selects between normal color (about as good a representation as is possible on a monitor) and lightened color (slightly easier to see the patch values).
(Checkbox) Zoom in so the data fills the image.
(Popup menu in the lower right of the Display area) Described above under 2D a*b* display.
u’v’ display for ColorChecker SG
7. Black & White density
Shows the grayscale response curve. Available for all currently-supported color charts because all of them contain grayscale regions.
(Popup menu) allows you to select one of several B&W displays.
When the B&W density plot is displayed, you can enter the incident lux level into a box in the Display area on the lower right of the Multicharts window. If the value is a positive number (not blank or zero) ISO Sensitivity will be calculated and displayed on the plot.
Log pixels vs. input density for Q-13
8. 3D L*a*b*
Displays patch values in 3D CIELAB L*a*b* space with a wireframe representing the boundaries of the selected color space. Ideal values are displayed as squares; Input values are displayed as circles. Can be zoomed and rotated; you need to rotate it to be able to visualize patch locations.
(Popup menu) Turns wireframe on, off, or on with minimal (coarse) grid.
(Toggle button; short for Auto rotate) starts rotating the image. This provides a better visual indication of the color locations. The image continues to rotate until the next time you press the button. It’s best to turn off rotation before switching to other views.
(Slider; default = 1) sets the wireframe transparency.Reducing transparency below 1 differentiates patches outside and inside the wireframe gamut boundary. Results are not reliable: patches near the boundary don’t always appear as they should.
(Slider) sets the background gray level.
(Popup menu in the lower right of the Display area) Described above under 2D a*b* display.
(Checkbox) Zoom in so the data fills the image.
3D L*a*b* display for ColorChecker
Duplicates the display of hardware vectorscopes, used for adjusting and calibrating broadcast and cinema cameras. It is designed to work optimally with the DSC Labs ChromaDuMonde 28 chart. (Other DSC charts will be added as customer demand warrants.)
There are several display options, including background color, reference and input display color. Light input colors (circles) and dark reference colors (squares) are shown on a dark background. HDTV, SDTV (similar to YCbCr below), and NTSC/PAL vectorscope patterns can be displayed. The recommended color space for these signals is sRGB. For now the vectorscope omits the standard target rectangles because the RGBCMY primaries in the CDM chart are different from the standard color bars.
This image is a preview of a full-featured vectorscope function that will be included in an upcoming broadcast/cinema version of Imatest that continuously refreshes frames from a video stream using the button instead of reading individual images from files.
11. Noise analysis (for charts with large enough patches)
Multicharts supports a variety of noise and SNR (Signal-to-Noise Ratio) analyses, including plain pixel noise, chroma noise, CIELAB (L*a*b*) noise, Dynamic Range analysis, and ISO 15739 visual noise. These measurements are for the grayscale patches.
The measurements include a set of measurements for all patches (color as well as grayscale) that is meaningful for undemosaiced raw images (i.e., no tonal response curve or color matrix applied). In such systems, noise is proportional to a constant plus the square root of the pixel level. This measurement allows you to determine the sensor dynamic range (using a fairly reliable extrapolation).
See Multicharts/Multitest noise for more detail.
12. Display image
The image can be displayed to verify the region settings and to explore the patche images (under a variety of conditions– normal view, intensified color, lightened, etc.). Options:
Image display (dropdown menu; title not displayed due to space limitations) allows you to select Original image, individual channel (R, G, B, Y, mean), chroma-boosted image, lightened image (several versions), etc. Useful for finding issues in the image as a whole or in individual patches.
Display patch ROIs (checkbox) Turns red ROI rectangles on or off.
If Crop is checked, a dropdown menu is opened, just to the right of the Crop checkbox, that allows you to select Whole crop or the individual patch.
13. Read – color correct – Save image
Once a color correction matrix has been calculated, the matrix can be used to correct arbitrary images. To do so, select 11. Read – color correct – save image in the Display box on the right of the Multicharts window. The initial display on the left side contains the message, Press “Read image to correct”, then press “Save corrected image” if it looks OK., the color correction matrix and statistics, and two buttons: and .
In the case shown on the right, a (digital) CC20C (cyan) filter was applied to both the Colorchecker and Gallery image. The correction matrix was calculated for the filtered Colorchecker, then the filtered Gallery image (shown uncorrected on the top) was read in. The corrected image is shown on the bottom.
Color correction on an arbitrary scene
14. YCbCr plot
Displays results on the CbCr plane of YCbCr color space. Similar to the Vectorscope plot with SDTV selected.
Expand (Checkbox; available in several 2D plots) Zoom in so the data fills the image.
Displays H (Hue) angle and S (Saturation) radius for HSV and HSL color representations, respectively. These representations are relative to the color space gamut boundary, which is located at radius = S = 1, i.e., they are not device-independent.
Expand (Checkbox; available in several 2D plots) Zoom in so the data fills the image.
|H (Hue) and S (Saturation) from HSV||H (Hue) and S (Saturation) from HSL|
|You can find a nice introduction to Multicharts on the Multicharts Tour.|