BREAKING CHANGE(smartpdf): improve image generation quality and API consistency

- Renamed convertPDFToWebpPreviews to convertPDFToWebpBytes for consistency
- Added configurable scale options with DPI support
- Changed default scale to 3.0 (216 DPI) for better quality
- Added DPI helper methods and scale constants

readme.md

@@ -179,7 +179,7 @@ async function extractTextFromPdf() {
 ```
 
 ### Converting PDF to PNG Images
-Convert each page of a PDF into PNG images:
+Convert each page of a PDF into PNG images with configurable quality:
 
 ```typescript
 async function convertPdfToPng() {
@@ -189,9 +189,16 @@ async function convertPdfToPng() {
   // Load a PDF
   const pdf = await smartPdf.readFileToPdfObject('./document.pdf');
   
-  // Convert to PNG images (one per page)
+  // Convert to PNG images with default high quality (216 DPI)
   const pngImages: Uint8Array[] = await smartPdf.convertPDFToPngBytes(pdf.buffer);
   
+  // Or specify custom scale/DPI
+  const highResPngs = await smartPdf.convertPDFToPngBytes(pdf.buffer, {
+    scale: SmartPdf.SCALE_PRINT,  // 6.0 scale = ~432 DPI
+    maxWidth: 3000,               // Optional: limit maximum width
+    maxHeight: 4000               // Optional: limit maximum height
+  });
+  
   // Save each page as a PNG
   pngImages.forEach((pngBuffer, index) => {
     fs.writeFileSync(`page-${index + 1}.png`, pngBuffer);
@@ -201,6 +208,102 @@ async function convertPdfToPng() {
 }
 ```
 
+#### Understanding Scale and DPI
+PDF.js renders at 72 DPI by default. Use these scale factors for different quality levels:
+- `SmartPdf.SCALE_SCREEN` (2.0): ~144 DPI - Good for screen display
+- `SmartPdf.SCALE_HIGH` (3.0): ~216 DPI - High quality (default)
+- `SmartPdf.SCALE_PRINT` (6.0): ~432 DPI - Print quality
+- Custom DPI: `scale = SmartPdf.getScaleForDPI(300)` for 300 DPI
+
+### Converting PDF to WebP Images
+Generate web-optimized images using WebP format. WebP provides 25-35% better compression than PNG/JPEG while maintaining quality:
+
+```typescript
+async function createWebPImages() {
+  const smartPdf = await SmartPdf.create();
+  await smartPdf.start();
+  
+  // Load a PDF
+  const pdf = await smartPdf.readFileToPdfObject('./document.pdf');
+  
+  // Create high-quality WebP images (default: 3.0 scale = 216 DPI, 85% quality)
+  const webpImages = await smartPdf.convertPDFToWebpBytes(pdf.buffer);
+  
+  // Save WebP images
+  webpImages.forEach((webpBuffer, index) => {
+    fs.writeFileSync(`page-${index + 1}.webp`, webpBuffer);
+  });
+  
+  await smartPdf.stop();
+}
+```
+
+#### Creating Thumbnails
+Generate small thumbnail images for PDF galleries or document lists:
+
+```typescript
+async function createThumbnails() {
+  const smartPdf = await SmartPdf.create();
+  await smartPdf.start();
+  
+  const pdf = await smartPdf.readFileToPdfObject('./document.pdf');
+  
+  // Create small thumbnails (0.5 scale = ~36 DPI, 70% quality)
+  const thumbnails = await smartPdf.convertPDFToWebpBytes(pdf.buffer, {
+    scale: 0.5,      // Small readable thumbnails
+    quality: 70      // Lower quality for smaller files
+  });
+  
+  // Save thumbnails
+  thumbnails.forEach((thumb, index) => {
+    fs.writeFileSync(`thumb-${index + 1}.webp`, thumb);
+  });
+  
+  await smartPdf.stop();
+}
+```
+
+#### Constrained Dimensions
+Create previews with maximum width/height constraints, useful for responsive layouts:
+
+```typescript
+async function createConstrainedPreviews() {
+  const smartPdf = await SmartPdf.create();
+  await smartPdf.start();
+  
+  const pdf = await smartPdf.readFileToPdfObject('./document.pdf');
+  
+  // Create previews that fit within 800x600 pixels
+  const previews = await smartPdf.convertPDFToWebpBytes(pdf.buffer, {
+    scale: 1.0,          // Start with full size
+    quality: 90,         // High quality
+    maxWidth: 800,       // Maximum 800px wide
+    maxHeight: 600       // Maximum 600px tall
+  });
+  
+  // The method automatically scales down to fit within constraints
+  previews.forEach((preview, index) => {
+    fs.writeFileSync(`preview-constrained-${index + 1}.webp`, preview);
+  });
+  
+  await smartPdf.stop();
+}
+```
+
+#### WebP Options
+The `convertPDFToWebpBytes` method accepts these options:
+
+- `scale`: Scale factor for preview size (default: 3.0 for ~216 DPI)
+- `quality`: WebP compression quality (default: 85, range: 0-100)
+- `maxWidth`: Maximum width in pixels (optional)
+- `maxHeight`: Maximum height in pixels (optional)
+
+Common scale values:
+- `0.5`: Thumbnails (~36 DPI)
+- `2.0`: Screen display (~144 DPI)
+- `3.0`: High quality (~216 DPI, default)
+- `6.0`: Print quality (~432 DPI)
+
 ### Using External Browser Instance
 For advanced use cases, you can provide your own Puppeteer browser instance: