Preparing and Outputting Images
Decide the destination first
Screen, print, email attachment and web page each impose different limits. For screen output, pixel dimensions matter most - a 1200 px wide image fills a typical content column whatever the ppi field says. For print, resolution at final size matters: around 300 ppi, plus bleed (typically 3 mm) and crop marks so trimming does not leave white edges.
Format choice
- JPEG - photographs; lossy, adjustable quality (around 70–85 is fine for web); no transparency.
- PNG - lossless, sharp graphics, transparency; large for photos.
- GIF - 256 colours, simple animation; unsuitable for photographs.
- TIFF - archival and print workflows, lossless, large.
- PDF - client delivery and multi-page documents, can embed fonts and profiles.
Colour and sharpening for output
Convert to the right profile before export: sRGB for web and general use, a CMYK or printer-specific profile for commercial print, ideally with a soft proof to preview the shift. Sharpen after resizing, matched to the medium - print tolerates more than screen.
Metadata, watermarks, file size
Embed copyright and keywords where appropriate, but strip personal location data before publishing. Watermarks deter casual reuse without blocking the image. Optimise weight by cropping, resizing and adjusting quality rather than simply saving at maximum.
Worked rule: A4 is 210 × 297 mm; with 3 mm bleed all round that is 216 × 303 mm. At 300 ppi: 216 mm ÷ 25.4 × 300 ≈ 2551 px, 303 mm ÷ 25.4 × 300 ≈ 3579 px. Traps: the "72 ppi for web" myth, expecting transparency in JPEG, and upsampling a small file to reach print ppi.