Question 1

What is the difference between resizing and cropping an image?

Accepted Answer

Resizing changes the overall dimensions of the image, scaling all content proportionally (or non-proportionally). The entire image remains visible. Cropping cuts away part of the image to focus on a specific area — the dimensions change but the content that remains is at its original scale. Many resizing workflows combine both: first crop to the desired aspect ratio, then resize to the target pixel dimensions.

Question 2

What does 'maintaining aspect ratio' mean?

Accepted Answer

Aspect ratio is the width-to-height proportion (e.g. 16:9, 4:3, 1:1). Maintaining aspect ratio means if you change one dimension, the other adjusts automatically to preserve the original shape. A 1920×1080 image resized to width 960 with aspect ratio preserved becomes 960×540. Without aspect ratio preservation, you can set width and height independently — this stretches or squishes the image, which is usually undesirable unless you specifically need a fixed output size.

Question 3

What pixel dimensions should I use for common use cases?

Accepted Answer

Common target sizes: social media profile pictures — 400×400 (square); Twitter/X header — 1500×500; Open Graph / social share image — 1200×630; blog post hero — 1200×675 (16:9); retina display (@2x) — double the displayed size; email images — max 600px wide; app icon sets — 1024×1024 source (Xcode/Android Studio generate smaller sizes). For web: provide 1x and 2x via srcset, or use responsive images with sizes attribute.

Question 4

Does resizing down lose quality?

Accepted Answer

Resizing down (downscaling) generally produces good results using Lanczos or bicubic resampling — detail is reduced but the image looks sharp. Resizing up (upscaling) degrades quality because pixels are interpolated: the result looks blurry or pixelated compared to a true high-resolution original. AI upscaling tools (waifu2x, Real-ESRGAN) use neural networks to generate plausible detail, but cannot recover truly lost information. For web images, always start with the highest-resolution source.

bezplatné nástroje pro webové vývojáře

Změna velikosti obrázků

Režim změny velikosti

Rozměry

Výstupní formát

Vstupní obrázek

Jak funguje změna velikosti obrázků

Co nástroj dělá

Běžné případy použití pro vývojáře

Datové formáty, typy nebo varianty

Běžné nástrahy a okrajové případy

Kdy použít tento nástroj vs. kód