Guide

AutoCAD CTB (Color-Dependent Plot Style) : A plot style based on object color

If you work with AutoCAD plots, understanding ctb (Color‑Dependent Plot Style) is essential for controlling how colors print, what lineweights appear, and how drawings are standardized for construction, manufacturing or presentation. This guide explains what a CTB plot style is, why and when to use it, how to create and edit one, alternatives, common errors and fixes, and practical tips for production-ready plotting.

What is a CTB (Color‑Dependent Plot Style)?

A CTB (Color‑Dependent Plot Style) is an AutoCAD plot style table file (extension .ctb) that assigns plotting properties — such as lineweight, screening (print density), color, linetype, and plot styles — based strictly on an object’s color index (ACI). When a drawing uses a CTB, objects plot according to the color they carry (by layer color or object color), not by layer name or a named style.

Key points:

  • CTB maps AutoCAD Color Index (1–255) to plot settings.
  • Used widely in offices that standardize lineweights by color.
  • CTB is different from STB (named plot styles), which assign properties per object or layer by name.

Why use CTB (benefits and typical use cases)

  • Simplicity and legacy compatibility: Many offices and plotting templates are built around color‑to‑lineweight standards (especially ISO and some regional standards).
  • Consistency: Ensures predictable printed output across drawings when users assign standard colors.
  • Fast setup for multi‑discipline drawings: Disciplines that share color standards (e.g., red for centerlines, yellow for dimensions) can use one CTB for consistent prints.
  • Compatibility with older templates: Many legacy CAD projects and plotter workflows expect CTB files.

Typical use cases:

  • Architectural, structural, civil, and MEP firms that use color → lineweight standards.
  • Plotting to monochrome (black & white) PDF or physical plotters where color must control pen widths.
  • Standardized office plotting workflows using templates and batch plotting.

How CTB works — explanation for beginners

  • Each color index (ACI) in AutoCAD is mapped to a plot style in the CTB file.
  • When plotting, AutoCAD reads the drawing object’s color and applies the CTB mapping to determine the printed color, lineweight (thickness), and screening/transparency.
  • If a layer or object uses BYLAYER color, the object’s color is controlled by the layer color — CTB will apply the mapping for that color.
  • CTB does not use layer or object names; if you need per‑layer control independent of color, use named plot styles (STB) or layer lineweights.

Differences between CTB and STB (quick comparison)

  • CTB: Color‑dependent — plot settings follow the object’s color index.
  • STB: Named plot styles — plot settings are assigned by style name to objects/layers (independent of color).
  • To switch between systems, AutoCAD provides conversion tools (see “Switching between CTB and STB”).

Choose CTB when your office standard relies on color mapping; choose STB if you want style names and more explicit per‑object control.

Step‑by‑step — Create, load and edit a CTB file

  1. Open the Plot dialog (type PLOT or click the Printer icon).
  2. Under Printer/Plotter, choose your device (e.g., DWG To PDF.plotter).
  3. In Plot style table (pen assignments) pick an existing .ctb or click New to create a new one.
  4. If creating or editing, click Edit to open the Plot Style Table Editor.
    • You can switch between Form View (select a color and edit properties) and Table View (spreadsheet style).
  5. For each color (1–255), set:
    • Color to be printed (Black/White or color).
    • Screening (%) — controls density (100% = full ink, lower = lighter).
    • Lineweight — choose from AutoCAD lineweight options (e.g., 0.13mm, 0.25mm, 0.50mm).
    • Linetype, End and Join styles if needed.
  6. Save the CTB file with a descriptive name (e.g., OfficeStandard.ctb).
  7. Back in the Plot dialog or Page Setup Manager, choose that CTB for your layout or page setup and click Apply.

Notes:

  • Use Page Setup to assign a CTB to a layout permanently — good for standard sheet stacks.
  • For batch plotting, ensure all drawings reference the same CTB in their Page Setups.

Practical mapping examples (suggested defaults)

These are suggestions — adapt to your office standard:

  • Color 7 (White/Black) → Lineweight 0.50 mm (main outlines)
  • Color 1 (Red) → 0.35 mm (visible object lines)
  • Color 2 (Yellow) → 0.13 mm (dimensions, annotations)
  • Color 3 (Green) → 0.18 mm (secondary objects)
  • Color 4 (Cyan) → 0.25 mm (hidden lines)
  • Color 5 (Blue) → 0.70 mm (cutting plane)
  • Screening: keep at 100% for hard prints; reduce (e.g., 70–90%) for lighter fills.

Always document your mapping in an office CAD standard sheet.

How and when to edit CTB

When to edit:

  • When adopting new company lineweight rules.
  • To adapt a CTB to a different printer or PDF style.
  • To fix existing prints that show incorrect weights or colors.

How to edit:

  • Open the CTB via Plot Style Manager (type PLOTSTYLE and open the folder, or from Plot dialog > Edit).
  • Modify mappings per color, test by plotting to PDF, and iterate.
  • Save versioned CTB files (e.g., Office_CTBA_v1.ctb) to avoid accidental overwrites.

Testing tip: create a test drawing with common entities assigned the common ACI colors, then plot to PDF to verify results.

Alternative methods and workflows

  • Use STB (Named Plot Styles) when you need object-by‑object named assignments (not based on color).
  • Control appearance via layer lineweights and keep CTB simple (colors can still be mapped to print color).
  • Use Viewport overrides in layouts to control colors or layer states per viewport (useful for combining disciplines).
  • Use a plotter driver or PDF stylesheet at the printer/PDF level to adjust look after CTB mapping.

When collaborating, prefer sharing the CTB file with the drawing and setting up Page Setups that reference the CTB to avoid mismatches.

Switching between CTB and STB

  • To convert a drawing between color‑dependent (CTB) and named (STB) plot styles, use the AutoCAD command CONVERTPSTYLES.
  • Process:
    1. Open the drawing.
    2. Type CONVERTPSTYLES and follow the prompts to either convert to named plot styles (.stb) or to color‑dependent (.ctb).
  • After conversion, always check and adjust lineweights and mappings because the conversion tries to preserve appearance but may require tweaks.

Where CTB files are stored and how to share them

  • CTB files are saved as .ctb files in AutoCAD’s Plot Styles folder. Typical locations:
    • Windows: %appdata%\Autodesk\\Rxx.x\enu\Plotters\Plot Styles
  • To share:
    • Copy the .ctb file and send to colleagues.
    • Include the CTB in your project template folder and instruct team members to install it in their Plot Styles path.
    • Use a network folder or CAD manager distribution system for consistent usage.

Common errors and fixes

  • Problem: “Plot style table not applied” or changes don’t show on plot.
    • Fix: Ensure the correct Plot Style Table is selected in the Page Setup or Plot dialog and that you are plotting the correct layout. Confirm drawing is in CTB mode (not STB).
  • Problem: Lines print too thin or too thick.
    • Fix: Edit the CTB and adjust the lineweight for the color in question; verify object color vs layer color (BYLAYER vs BYBLOCK).
  • Problem: Everything plots black even when CTB maps colors to colors.
    • Fix: CTB can control printed color; ensure the CTB color assignment for that ACI is set to print color rather than forced to black. Also check the plotter/printer settings (some plotters default to monochrome).
  • Problem: Dashed or linetypes print solid.
    • Fix: Check lineweight scaling and plot resolution; ensure the linetype scale is appropriate and “Plot object lineweights” is enabled if required.
  • Problem: Team members plotting different results.
    • Fix: Confirm everyone uses the same CTB file version and the CTB is in their Plot Styles folder. Use shared Page Setups.

Tips for production and standards

  • Keep a master CTB file in version control or a shared network location.
  • Name CTB files clearly, e.g., CompanyName_Architect_CTBA.ctb.
  • Create a one‑page PDF that documents the color → lineweight mapping for designers to reference.
  • Use Page Setups in templates to ensure every new layout uses the appropriate CTB.
  • Test plots to the final output device (plotter or PDF) — screen preview may differ.
  • When collaborating with other firms, exchange CTB files before joint plotting to avoid mismatches.

FAQ

What is the main difference between CTB and STB?

CTB is color‑dependent (plotting properties are tied to the object’s ACI color). STB uses named plot styles assigned to objects or layers by style name (independent of color). Choose CTB for color‑to‑weight workflows, STB for named style workflows.

How do I convert a drawing from CTB to STB or vice versa?

Use the AutoCAD command CONVERTPSTYLES. Follow the prompts to convert and then verify lineweights and appearances after conversion.

Where do I put CTB files so AutoCAD can find them?

Place .ctb files in AutoCAD’s Plot Styles folder (commonly in %appdata%\Autodesk\\Plotters\Plot Styles). Alternatively, use a shared network location and inform users where to install them.

Why are my printed lines a different thickness than on screen?

On‑screen display depends on lineweight display settings and zoom level. The CTB controls the actual plot lineweight. Always test by plotting to PDF or a printer and verify CTB mappings.

How can I ensure my team uses the same CTB settings?

Store the CTB in a shared project folder or intranet, include it in your CAD template, and document the mapping. Use Page Setups that reference the CTB and distribute those templates to all users.

Can CTB control color when plotting to color PDF or full‑color outputs?

Yes — CTB can specify the printed color for each ACI. You can map ACI to print in black/white or to a specific color as needed.

My linetypes print as continuous lines — what should I check?

Check linetype scale and plotting resolution, confirm lineweights aren’t too heavy (which can hide dashes), and ensure the linetype is loaded and set correctly for the objects. Also verify the viewport scale and “Linetype scaling” settings.

Can I use CTB with viewport overrides?

Yes. Viewports can override layer visibility and properties, but the CTB will still map colors to plot properties. Use viewport overrides to show different disciplines while using the same CTB.

If you want, I can provide a downloadable example CTB mapping for architectural standards (with recommended ACI-to-lineweight values) that you can import and test in AutoCAD.

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