DPI and Resolution
Resolution describes how many pixels an image contains—width and height in pixels. DPI (dots per inch) and PPI (pixels per inch) describe how those pixels map to physical print size. A twenty-four hundred pixel wide image is twenty-four hundred pixels on screen regardless of whether metadata claims seventy-two or three hundred DPI. Browsers lay out images by pixel dimensions and CSS, not by DPI labels alone.
Print workflows use DPI to calculate inches: three thousand pixels at three hundred DPI equals ten inches wide on paper. Web workflows use CSS pixels and device pixel ratios. Serving a four-thousand-pixel image in a four-hundred-pixel layout wastes bandwidth because the browser downscales. Target roughly one to two times your layout width in source pixels for sharp retina displays.
FileShrinkr scales very wide uploads to practical maximums for compression and PDF export. Focus on pixel dimensions when tuning quality; changing DPI metadata without resampling does not shrink on-screen file appearance. Match pixel targets to channel—email, hero banner, thumbnail—and compress after resizing for predictable results.