The Grapher

From ColorWiki

Go back to the previous section: Profile Renamer.

Color information can be complicated, and 2D and 3D graphs aid visualization and help evaluate profiles, devices and printing processes.

The Grapher will plot the gamut volume (or outline) of ICC device profiles, space profiles and the color list from Named Color Profiles (NCP) in (Y)xy, (L)uv, or (L)ab coordinates. It will also plot color lists resulting from measurement data, synthetic test data and image file colors.

The Grapher uses the absolute colorimetric rendering intent for all functions (unless otherwise noted.) To graph using other rendering intents use ColorThink Pro.

Device profiles include

• Scanner/Camera (“scan”),
• Monitor (“mntr”),
• Printer (“pntr”) types.

Gray scale profiles, device Link (“link”)and abstract (“abst”) profiles have no discernible gamut and therefore cannot be plotted.

Unless otherwise stated, the following graph controls and plot item options apply to both 2D and 3D graphing modes in any of the three available coordinate systems.

Contents 1 Creating Graphs 2 Controlling Graphs using the Mouse 3 Plot Items 4 Plotting styles 5 Volume 6 Plot Item Types 7 Dimensions 8 Coordinates 9 Spin Control 10 Axes & Labels 11 Saving Graphs

Creating Graphs

• Click the 2D or 3D Grapher button on the menu bar to open an empty graph .
• Click the 2D or 3D Grapher button on the menu bar of the Profile Inspector, Image Inspector, or Color List windows.
• Select Graph:Open 2D Graph or Graph:Open 2D Graph from the pull down menus.
• Drag a color, color list, image, or profile (either from within ColorThink or directly from the Finder) onto a 2D or 3D Grapher button.

Controlling Graphs using the Mouse

The ColorThink Grapher was designed so manipulation of the plot item display was intuitive and powerful. The mouse plays an important role in this ability.

• Click-drag to rotate the graph left-right or up-down.
• Shift-Click-drag to “shift” the graph around the screen
• Option-Click-drag and then drag the mouse “up” and “down” to zoom in and out. Try zooming all the way inside a profile’s gamut to view it from the inside.

Plot Items

To Add plot Items

• Drag the icon representing the item (color, color list, image, or profile) onto the Grapher window either from within ColorThink or directly from the Finder.
• Choose an item from the “Add” popup menu located immediately below the “Plot Items” list box.
• Click the 2D or 3D Grapher button on the menu bar of the Profile Inspector, Image Inspector, or Color List windows.

To Remove plot Items

• Select the plot item from the Plot Item list and press the Delete key.

To Show & Hide plot items

• Check or uncheck the box to the left of the plot item in the Plot Item list box.
• Checking the box will also select the plot item. Unchecking a box will not select the plot item.

To Highlight a profile (2D only)

• Select the item in the plot list

To set Plot Colors

• Select the item in the plot list
• Select:

• True Colors – All color points and vertices are colored using the actual Lab color values processed through the current monitor profile. Colors outside the gamut of the monitor will be plotted as the closest possible color (using the relative colorimetric rendering intent and the current color management module.)

• Single Colors – All colors in the plot item will be colored using a single color. The next available single color will be selected for the plot item. To change the plot color, select a different color from the adjacent popup menu.

• Delta-E Coloring (available in Vector mode only). Delta-E coloring will color the vectors (color shifts) in a plot item using green/yellow/orange/red depending on the amount of color shift depicted by the vector. To change the criteria for the error levels at which the color changes occur, select the “Delta-E Colors” tab and move the sliders in the color bar. In this manner you can select your shop-standard error levels and evaluate color shifts according to your own standards.

• Tone using L* - For true-color accuracy ColorThink darkens the colors plotted according to the Lightness ("L" component of Lab) value of the color. This can cause dark colors to become invisible against dark backgrounds. Uncheck this box to remove the darkening effect and lighten the dark portion of the plot item. The colors are less accurate but details in shadow colors are much more visible.

Opacity

To vary the Opacity (transparency) of a plot item:

• Select the plot item in the list
• Drag the Opacity slider left or right to decrease or increase the opacity of the plot item.

This is especially helpful for turning a profile gamut volume transparent so color data or other profile gamuts located inside or behind the current profile are visible. Please refer to the Tutorials section for an example of this technique.

Plotting styles

Points

Use the Size slider to change the size of each color point plotted.

Vectors

Plotting colors as vectors allows a graphical view of color shifts in 2 or 3 dimensions. This is a powerful technique to quickly get a feeling for how color shifts are occurring in different colors (different areas of the 3D color space) and what types of shifts (lightening/darkening, hue shifts, saturation changes) are occurring.

Vectors can be used to:

• compare two sets of measurement files showing:

• color shifts as inks dry
• differences between papers
• differences between ink sets
• differences between printers

• compare two sets of image data showing color shifts after applying profiles or performing color edits.
• Show color shifts as profiles are applied to either color lists or image data.

To plot as vectors

• Select an Image or Color List plot item and click the “Vectors” button.

(A “destination” box will appear.)

• Drag your comparison data or a profile into the destination box. Comparison data can be another color list or an image file. It is suggested the original color list and the “destination” color list have the same number of colors. If the number of colors in each list differs, ColorThink will plot all the vectors for which a color exists in each list. Additional colors in the longer list will be ignored.

If you drag a profile into the “destination” box, ColorThink will “round trip” the color list and show the color shift that occurs as a result of this conversion. This round trip consists of a conversion from Lab to the color space of the device profile and then a conversion back to Lab using the same profile. Assuming the “back” or “proofing” conversion of the profile is accurate, this round trip transform will show how much color shift occurs as a result of the profile application. You will see out-of-gamut colors shift in-gamut to as to become printable, in-gamut colors shift due to perceptual renderings or profile errors.

To change the rendering intent used for the conversion (the Lab- >device part of the conversion):

• Select the rendering intent from the “Intent” popup menu.

ColorThink will recalculate the color shifts using the new intent. The vectors will look like little tadpoles. The dot will appear at the end of the vector and represent the color that is second in the list of plot items. Think of it as the first list is the "before" and the second list the "after".

This feature can be very useful for viewing device drifts, how different printer/ink/media settings affect color, or how different filters on your reading device affect the color values.

Volume

When plotting profiles, ColorThink shows the device gamut captured by the profile using a gamut volume shape (for 3D graphs) or a gamut outline (for 2D graphs). ColorThink uses the Absolute Colorimetric table in the Device-to-Lab transform to accurately calculate the device volume. The appearance of that volume can be in three different styles:

• Wireframe – This is the simplest plot and joins the vertex points together using lines. Linearity/calibration of the profiled device shows as differing spaces between the lines.
• Flat – Each 4-sided polygon on the gamut surface is rendered using a single, solid color. This effectively shows the gamut volume, the linearity/calibration of the device and the color representation of the locations in the Lab colorspace.
• Smooth – Each polygon’s color is rendered smoothly, blending the different corner colors across the surface of the polygon. This is the most accurate color rendering of the surface of the device gamut but at the expense of gamut surface detail.

See the tutorial section for an example of how to use these different styles along with varying gamut volume opacity to clearly compare and contrast two device gamuts.

Plot Item Types

Colors, Color Lists, & Images

• Will display as flat squares (fastest), cubes or spheres
• May be plotted as Points or Vectors.

Profiles

To change profile volume resolution:

• For profiles that have fluctuations along the gamut boundary, higher resolutions can be selected by choosing a different resolution button.

To plot the Gamut Projection:

• A projection of the gamut can be plotted for reference. Check the “Plot gamut projection” option. A line depicting the outer edges of the most saturated colors is plotted below the profile.

The graph control panel appears as a floating window in Mac OS X and as a sheet attached to the Grapher window in Windows. To show the graph control panel as a sheet, move the mouse pointer until it is just below the title bar of the Grapher window, centered near the “Grapher” window name. The sheet will slide out for you to make changes and then slide away when you move the point away from the control panel.

Dimensions

To select 2D or 3D:

• Click on the 2D or 3D radio button and ColorThink will change to that graphing mode.

In each coordinate system, graphing in 2D removes the lightness component and the chromatic component is the only information plotted. As a result, the graphs show the outer edges of the gamut regardless of the lightness level of this information. For lightness information in addition to the chromatic information, use the Grapher in 3D mode.

3D graphs have the ability to display much more information than 2D graphs. Subtle gamut differences and color shifts are represented in 3D that are not possible in 2D. For example, in evaluating an inkjet printer which may be used for proofing purposes, it is important to determine that the inkjet can reach the same black point that the press or analog proof to be simulated is able to produce. In 3D it is immediately apparent when a proofer will not get dark enough whereas a 2D-gamut overlay would not reveal this information and the proofing printer might have mistakenly been deemed appropriate for the task.

Coordinates

To select the graphing dimension:

• Click on the Lab, Yxy, or Luv to change the graphing dimension:

The Yxy Chromaticy diagram is a popular 2D method for illustrating the gamut differences between different devices or printing methods. Yxy, however, is not perceptually uniform and so does not give an accurate illustration of gamut shape and size. For example, the greens in the Yxy diagram are exaggerated and plot covering a larger area than greens actually represent in our perception. For this reason Luv is included as a graphing coordinate system. Luv is designed to be more perceptually uniform than Yxy and the area devoted to each color more in line with our perception. The Lab coordinate system is also offered as a graphing option. Lab also offers a reasonable gamut shape and size representation but many claim it also suffers from areas of perceptual non-uniformity.

In general we recommend the Yxy or Luv coordinates for 2D graphing only. Lab has been found to be easier to visualize, understand, and compare when creating 3D graphs.

Spin Control

The spinning of the plot items in the graph can be controlled several ways:

• None Plot items can be “grabbed” and rotated by clicking on the graph window and dragging left-right or up-down. The plot items will not rotate on their own, however.
• Inertia Plot items can be rotated as in “None” but if the mouse button is released while moving, the plot items will continue to rotate at the speed at which they were released. <default>. Use the <- and -> arrow keys on the keyboard to “nudge” the display left and right. Each nudge will increase the rate of rotation.

- Continuous: Plot items will continue to rotate at a constant speed in one direction.

Axes & Labels

• Check the “Plot [vertical] axis” or “Plot [cross] axes" options to plot lines for the axes. This can help with the visualization of color spaces.

Spectrum Locus

• Check the “Plot Spectrum Locus” box.

The Spectrum Locus is the curve defined by “pure” wavelengths of light plotted from 380nm to 730nm. The spectrum locus demarks the outer range of human perception – effectively the gamut of the human eye. The spectrum locus option is only available in the Luv and Yxy color spaces. Lab, by definition, is bounded by the human eye gamut. While Lab contains numbers that do not correspond to human-perceptible colors, the shape of the visible color gamut is difficult to determine and plot.

Background

Changing the Background slider will vary the brightness of the background.

Saving Graphs

ColorThink can save the graph window as an image in either "BMP" format (Windows version) or "PICT" format (Mac version).

1] Go to File, Save as BMP image (Windows) or Save as PICT image (Mac)

2] Choose a file name for the image and the location at which you wish to store it.

Note: The size of the saved image is dependent on the size of the grapher window. See Window size for instructions on how to change the size of the grapher window.

Go to the next section: Color Lists