EPUBs allow images to enhance and expand digital publications. However, optimization is crucial for delivering seamless reading experiences across devices. Follow key recommendations on image sizing, formats, and compression.
Choose Optimal Sizes for Reading
Digital screens have lower resolution than print. Size images accordingly. For e-readers with ~167 ppi displays, ideal width is 1500 px or below. On tablets (~264 ppi), 2500 px width suffices. Excessively large images slow EPUB loading.
Select Web-Ready Image Formats
JPEG is the norm for photographs. PNG handles illustrations with flat colors or transparency. GIFs work for simple images with limited colors. Avoid print formats like TIFF and BMP—these bloat EPUBs with unnecessary data. Lean web formats optimize for screens.
Balance Quality and Size with Compression
Heavier compression shrinks images but reduces quality. Light compression maintains quality at larger file sizes. For EPUBs, aim for 60-80% JPEG quality, and PNG-24 with adaptive filtering. Assess visually: some artifacting is acceptable if images remain crisp and legible.
Run Optimization Tools to Refine
After manual optimization, tools like ImageMagick further refine images. Scripts convert formats, strip metadata, and compress without visual loss. Some compress better than native apps. Automated batch optimization streamlines EPUB image prep.
Recheck On Reading Devices
Preview on actual e-readers. Zoom images at 100% to check resolution and compression artifacts. Refine techniques if pixels appear distorted or blurry. On tablets, confirm responsiveness across orientations. Optimize until images render sharply at reading sizes.
Conscientious image optimization keeps EPUBs lean and responsive across devices. With a sharp focus on sizing, formats, compression and testing, you deliver engaging visuals readers can smoothly enjoy.