This is a common issue when dealing with PDFs created from images. Let’s break it down:

Why the Second PDF Might Still Be Large:

1. Image Compression During PDF Creation:

   • macOS's built-in PDF creation tools (e.g., Preview) often use default settings that may not recompress images optimally. Even if you resize the images, the tool might still save them in a format or quality that isn't very space-efficient.
   • Some tools embed images in their original format (e.g., PNG for lossless) rather than converting them to more efficient formats like JPEG.

2. Embedded Metadata:

   • Resizing the images might strip some metadata, but in some cases, PDF creation tools might add additional metadata or encoding overhead, causing file size to grow.

3. File Format Differences:

   • PNGs are lossless and can still have larger file sizes than compressed JPEGs. Even resized, a PNG can still inflate the PDF size if not optimized during creation.

4. Image DPI (Dots Per Inch):

   • The resized images might still have a higher DPI than needed for viewing or printing. Many tools don’t reduce DPI appropriately during the PDF creation process.

5. Redundant Embedded Fonts or Objects:

   • If the PDF includes text or objects, macOS might embed unnecessary fonts or objects, contributing to file size.

How to Properly Optimize Your PDF:

To ensure smaller PDF sizes, follow these steps:

Step 1: Optimize Images Before PDF Creation

• Resize to Target Resolution: Ensure images are resized to a reasonable DPI for your purpose. For screen viewing, 72–96 DPI is enough; for printing, 300 DPI is standard.
• Choose JPEG Over PNG: For photographic images, save them as compressed JPEGs. Use PNG only for images that need transparency or sharp edges (like logos or illustrations).
• Compress Images: Use an image optimizer like ImageOptim (Mac-compatible) or online tools (e.g., TinyPNG, JPEGmini).

Step 2: Use Specialized Tools for PDF Creation

• Avoid using macOS Preview if you need better compression control. Instead, use:
  • Adobe Acrobat Pro: Offers advanced options for downsampling images, recompressing them, and removing redundant data.
  • IronPDF: If you're coding a solution, this library allows fine-tuned compression settings.
  • Free PDF Tools: Tools like Sejda, PDFsam, or PDF24 provide good compression capabilities.

Step 3: Optimize an Existing PDF

If you already have a large PDF, use optimization tools:

1. Adobe Acrobat Pro:
   • Open the PDF and select File > Save As Other > Optimized PDF.
   • Adjust image compression, resolution, and other settings.
2. Ghostscript (Free):
   • Use this command-line tool for advanced optimization:

     bash
     複製程式碼
     gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook \
     -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf
     

     Replace /ebook with /screen for even smaller sizes.
3. Online Compressors:
   • Tools like iLovePDF or SmallPDF let you upload and compress PDFs.

Step 4: Remove Unnecessary Data

• Use a PDF editor to strip unnecessary fonts, metadata, or annotations.
• Flatten the PDF if it contains interactive elements or layers (this can reduce complexity).

Key Recommendations:

• Use tools with explicit control over compression (like Acrobat or Ghostscript).
• Optimize your images carefully before creating the PDF.
• Experiment with different compression settings when exporting the PDF.

Would you like help with a specific tool or process? For example, if you’re interested in using IronPDF or Ghostscript, I can guide you further.

Ghostscript is a powerful command-line tool for working with PDFs, including optimization. Here’s a step-by-step guide to using it for your needs:

Installing Ghostscript

1. macOS Installation:
   • Use Homebrew (if not installed, first install Homebrew from brew.sh):

     bash
     複製程式碼
     brew install ghostscript
     

   • Confirm installation by running:

     bash
     複製程式碼
     gs --version
     

Optimizing a PDF with Ghostscript

The command for optimizing a PDF typically looks like this:

bash
複製程式碼
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook \
-dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf

Explanation of Parameters:

• -sDEVICE=pdfwrite: Sets Ghostscript to produce a PDF output.
• -dCompatibilityLevel=1.4: Ensures the PDF is compatible with older viewers (you can also use 1.5 or higher for modern use).
• -dPDFSETTINGS: Determines compression level:
  • /screen: Low quality, smallest size (72 DPI images).
  • /ebook: Medium quality (150 DPI images).
  • /printer: High quality (300 DPI images).
  • /prepress: Best quality for professional printing.
  • /default: Default compression.
• -dNOPAUSE: Prevents Ghostscript from pausing for user interaction.
• -dQUIET: Suppresses non-critical messages.
• -dBATCH: Ensures Ghostscript exits after processing.
• -sOutputFile=output.pdf: Specifies the output file name.
• input.pdf: The input file name.

Examples

1. Compress for On-Screen Viewing:

   bash
   複製程式碼
   gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/screen \
   -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf
   

2. Compress for Ebooks:

   bash
   複製程式碼
   gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook \
   -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf
   

3. Compress for High-Quality Printing:

   bash
   複製程式碼
   gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/printer \
   -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf
   

Advanced Options

1. Custom DPI Settings: If the predefined /screen, /ebook, etc., options don’t meet your needs, you can manually control the resolution:

   bash
   複製程式碼
   gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 \
   -dDownsampleColorImages=true -dColorImageResolution=100 \
   -dDownsampleGrayImages=true -dGrayImageResolution=100 \
   -dDownsampleMonoImages=true -dMonoImageResolution=100 \
   -dNOPAUSE -dQUIET -dBATCH -sOutputFile=output.pdf input.pdf
   

   Replace 100 with your desired DPI.

2. Remove Metadata: Ghostscript automatically removes some metadata, but for further cleanup, you can preprocess with tools like exiftool or online services.

Batch Processing PDFs

If you have multiple PDFs to optimize, you can use a loop in the terminal:

bash
複製程式碼
for file in *.pdf; do
   gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook \
   -dNOPAUSE -dQUIET -dBATCH -sOutputFile="optimized_$file" "$file"
done

Testing Different Settings

Run the commands with /screen, /ebook, and /printer to compare the quality and size of the resulting PDFs. This helps you decide which option works best for your needs.

Let me know if you'd like help customizing these commands or troubleshooting issues!

To simplify the process of creating an optimized PDF directly from images in a specific folder using Ghostscript, we can follow these steps:

Step 1: Prepare the Images

• Ensure the images (e.g., JPG, PNG) are stored in a specific folder, say /path/to/your/images.
• Sort the files if necessary (e.g., alphabetically or numerically) to control the order they appear in the PDF.

Step 2: Create a PDF from the Images

Ghostscript doesn’t natively convert images into PDFs directly, but macOS includes the sips tool, which can batch convert images to individual PDFs. You can then merge those PDFs using Ghostscript.

Here’s a streamlined approach:

Command to Batch Convert Images to PDFs

Run the following in your terminal:

bash
複製程式碼
mkdir /path/to/your/output_pdfs
for img in /path/to/your/images/*.{jpg,png}; do
   sips -s format pdf "$img" --out "/path/to/your/output_pdfs/$(basename "$img" .jpg).pdf"
done

• Replace /path/to/your/images with the folder containing your images.
• Replace /path/to/your/output_pdfs with the folder where you want the individual PDFs saved.

Command to Merge PDFs into a Single File

Once the individual PDFs are created, merge them into one PDF using Ghostscript:

bash
複製程式碼
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook \
-dNOPAUSE -dQUIET -dBATCH -sOutputFile=merged.pdf /path/to/your/output_pdfs/*.pdf

Step 3: Combine and Optimize Directly Using ImageMagick (Alternative Option)

If you'd like an all-in-one tool, ImageMagick can convert and optimize images directly into a single PDF.

1. Install ImageMagick (via Homebrew):

   bash
   複製程式碼
   brew install imagemagick
   

2. Create and Optimize PDF: Use this command to import all images from a folder, convert them into a single PDF, and compress the output:

   bash
   複製程式碼
   magick /path/to/your/images/*.{jpg,png} -quality 85 -density 150 -compress JPEG output.pdf
   

   • -quality 85: Adjusts JPEG compression quality (lower values = smaller size).
   • -density 150: Sets the DPI for images in the PDF (e.g., 150 DPI is suitable for viewing).
   • -compress JPEG: Ensures all images are stored as JPEG in the PDF.

Step 4: Automating the Entire Process

Create a shell script to automate everything (convert images, merge PDFs, and optimize):

Shell Script Example

Save the following to a file (e.g., optimize_pdf.sh):

bash
複製程式碼
#!/bin/bash

# Define paths
IMAGE_FOLDER="/path/to/your/images"
OUTPUT_PDFS="/path/to/your/output_pdfs"
FINAL_PDF="output.pdf"

# Create output folder if it doesn't exist
mkdir -p "$OUTPUT_PDFS"

# Convert images to individual PDFs
for img in "$IMAGE_FOLDER"/*.{jpg,png}; do
    sips -s format pdf "$img" --out "$OUTPUT_PDFS/$(basename "$img" .jpg).pdf"
done

# Merge PDFs into one and optimize
gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/ebook \
-dNOPAUSE -dQUIET -dBATCH -sOutputFile="$FINAL_PDF" "$OUTPUT_PDFS"/*.pdf

echo "Optimized PDF created: $FINAL_PDF"

Run the Script

1. Make the script executable:

   bash
   複製程式碼
   chmod +x optimize_pdf.sh
   

2. Run it:

   bash
   複製程式碼
   ./optimize_pdf.sh
   

Final Notes

This approach ensures you:

• Convert images to PDFs efficiently.
• Merge and optimize the final output using Ghostscript.

Would you like me to refine the script further or assist in testing it?