pnas-figure-guide

PNAS Figure Preparation Guide

Overview

This guide provides the complete specifications for preparing figures for submission to PNAS (Proceedings of the National Academy of Sciences). PNAS is notable for its strict RGB-only policy (CMYK submissions are returned), italicized uppercase panel labels, and automated image screening software.

Official reference: https://www.pnas.org/author-center/submitting-your-manuscript

Resolution Requirements

| Image Type | Minimum Resolution | Notes | |---|---|---| | Halftones (color/grayscale photos) | 300 PPI | At publication size | | Combination artwork (MS Office) | 600-900 DPI | Mixed text and images | | Line art (bitmap text/thin lines) | 1,000 PPI | At publication size | | LaTeX figures | — | High-quality PDF or EPS |

from PIL import Image

def check_pnas_resolution(image_path, image_type='halftone'):
    """Check if image meets PNAS resolution requirements.

    Args:
        image_type: 'halftone' (300), 'combination' (600), or 'lineart' (1000)
    """
    min_ppi = {'halftone': 300, 'combination': 600, 'lineart': 1000}
    required = min_ppi.get(image_type, 300)

    img = Image.open(image_path)
    dpi = img.info.get('dpi', (72, 72))

    print(f"Type: {image_type} | Required: {required} PPI | Actual: {dpi[0]} PPI")

    if dpi[0] >= required:
        print("PASS")
    else:
        print(f"FAIL: Need {required} PPI minimum")

    return dpi[0] >= required

File Format

| Format | Accepted | |---|---| | TIFF | Yes (preferred for raster) | | EPS | Yes (fonts must be embedded) | | PDF | Yes (fonts must be embedded) | | PPT | Yes | | 3D images | PRC or U3D with 2D representation (TIFF/EPS/PDF) |

Submission Stages

• Initial submission: Format-neutral — single PDF containing full manuscript, figures, and SI. High-resolution files not required.
• Production phase: Separate high-resolution figure uploads required.

Figure Size and Dimensions

IMPORTANT: Provide images at final publication size, not full-page size.

| Layout | Width | |---|---| | 1 column | 8.7 cm (3.43 in) | | 1.5 columns | 11.4 cm (4.5 in / 27 picas) | | 2 columns | 17.8 cm (7.0 in / 42.125 picas) | | Maximum height | 22.5 cm (9 in / 54 picas) |

import matplotlib.pyplot as plt

PNAS_WIDTHS = {
    'single':  8.7 / 2.54,   # 3.43 inches
    'middle':  11.4 / 2.54,  # 4.49 inches
    'double':  17.8 / 2.54,  # 7.01 inches
}
PNAS_MAX_HEIGHT = 22.5 / 2.54  # 8.86 inches

def create_pnas_figure(layout='single', aspect_ratio=0.75):
    """Create a Matplotlib figure sized for PNAS."""
    width = PNAS_WIDTHS[layout]
    height = min(width * aspect_ratio, PNAS_MAX_HEIGHT)

    fig, ax = plt.subplots(figsize=(width, height))
    fig.set_dpi(300)
    return fig, ax

Color Mode

CRITICAL: RGB Only

• Submit in RGB color mode ONLY
• CMYK submissions will be returned for correction
• Tag RGB images with originating ICC profile for accurate RGB-to-CMYK conversion
• PNAS manages print conversion using calibrated profiles

from PIL import Image

def validate_pnas_color_mode(image_path):
    """PNAS strictly requires RGB. CMYK will be rejected."""
    img = Image.open(image_path)

    if img.mode == 'CMYK':
        print("REJECTED: PNAS does not accept CMYK images")
        print("Action: Convert to RGB before submission")
        return False
    elif img.mode in ('RGB', 'RGBA'):
        print("PASS: Image is in RGB mode")
        return True
    else:
        print(f"WARNING: Unexpected mode '{img.mode}'; convert to RGB")
        return False

def convert_to_rgb(image_path, output_path):
    """Convert any image to RGB for PNAS submission."""
    img = Image.open(image_path)
    if img.mode != 'RGB':
        img = img.convert('RGB')
        print(f"Converted from {img.mode} to RGB")
    img.save(output_path)

Font Requirements

| Element | Specification | |---|---| | Approved fonts | Arial, Helvetica, Times, Symbol, Mathematical Pi, European Pi | | Font size | 6-8 pt at final publication size (minimum 2 mm when printed) | | Consistency | Same font for all figures in manuscript | | Text type | Vector text preferred (scales cleanly) | | Embedding | All fonts must be embedded in EPS and PDF files |

Panel Labels (PNAS-Specific Convention)

• Italicized uppercase letters: A, B, C, D, ...
• This is a distinctive PNAS convention — different from most other journals

import matplotlib.pyplot as plt

def set_pnas_fonts():
    """Configure Matplotlib for PNAS figure fonts."""
    plt.rcParams.update({
        'font.family': 'sans-serif',
        'font.sans-serif': ['Arial', 'Helvetica'],
        'font.size': 7,
        'axes.labelsize': 7,
        'axes.titlesize': 7,
        'xtick.labelsize': 6,
        'ytick.labelsize': 6,
        'legend.fontsize': 6,
    })

def add_pnas_panel_labels(fig, axes):
    """Add PNAS-style italicized uppercase panel labels."""
    import string
    if not hasattr(axes, '__iter__'):
        axes = [axes]

    for i, ax in enumerate(axes):
        label = string.ascii_uppercase[i]
        ax.text(-0.1, 1.1, label,
                transform=ax.transAxes,
                fontsize=8,
                fontstyle='italic',
                fontweight='bold',
                va='top',
                ha='right',
                fontfamily='Arial')

Labeling Conventions

• Panel labels: Italicized uppercase (A, B, C)
• All text, numbers, letters, symbols: 6-12 pt (2-6 mm) after reduction
• Text sizing must be consistent within each graphic
• Labels should match body text font conventions

Image Integrity and Manipulation Policy

PROHIBITED

• Enhancing, obscuring, moving, removing, or introducing any specific feature within an image

PERMITTED

• Brightness, contrast, color balance adjustments applied to the whole image without obscuring or eliminating original information (including backgrounds)

REQUIRED

• When combining images from multiple sources: make explicit by arrangement and figure legend text
• Name processing software in Methods section
• Indicate all manipulations in figure legends
• Original data must be available on request (missing data may result in rejection)

Automated Screening

PNAS uses screening software to detect:

• Cloning and pasting artifacts
• Suspicious contrast adjustments that obscure data
• Inconsistent background pixelation
• Other signs of inappropriate image manipulation

Accessibility

• Beginning with Volume 123, PNAS includes alt text for all journal figures to improve digital accessibility

Python Quick Start: Full Validation

from PIL import Image
import os

def validate_pnas_figure(image_path, image_type='halftone', layout='single'):
    """Full validation of a figure against PNAS requirements."""
    img = Image.open(image_path)
    issues = []

    # 1. Resolution check
    min_ppi = {'halftone': 300, 'combination': 600, 'lineart': 1000}
    required = min_ppi.get(image_type, 300)
    dpi = img.info.get('dpi', (72, 72))
    if dpi[0] < required:
        issues.append(f"Resolution {dpi[0]} PPI below {required} PPI for {image_type}")

    # 2. STRICT RGB check
    if img.mode == 'CMYK':
        issues.append("REJECTED: CMYK not accepted. Must convert to RGB")
    elif img.mode not in ('RGB', 'RGBA'):
        issues.append(f"Color mode '{img.mode}' not standard; use RGB")

    # 3. Dimension check at publication size
    widths_cm = {'single': 8.7, 'middle': 11.4, 'double': 17.8}
    max_height_cm = 22.5
    if layout in widths_cm and dpi[0] > 0:
        actual_w_cm = (img.size[0] / dpi[0]) * 2.54
        actual_h_cm = (img.size[1] / dpi[1]) * 2.54
        target_w = widths_cm[layout]
        if actual_h_cm > max_height_cm:
            issues.append(f"Height {actual_h_cm:.1f} cm exceeds max