Resize & Crop

Basic resize

Param	Type	Range	Description
w	integer	1-8192	Target width in pixels
h	integer	1-8192	Target height in pixels
dpr	integer	1-3	Device pixel ratio multiplier

?w=800          → 800px wide, height auto
?h=600          → 600px tall, width auto
?w=800&h=600    → 800x600 (behavior depends on fit mode)
?w=400&dpr=2    → 800px actual (for 2x displays)

Fit modes

Control how the image is resized when both w and h are specified.

Mode	Param	Behavior
Cover	fit=cover	Fill the target area, crop overflow (default)
Contain	fit=contain	Fit within the target area, preserve aspect ratio
Fill	fit=fill	Stretch to exactly fill (may distort)
Scale down	fit=scale-down	Like contain, but never upscales
Crop	fit=crop	Same as cover (explicit crop intent)
Pad	fit=pad	Contain + pad with background color

?w=800&h=600&fit=cover      → fills 800x600, crops overflow
?w=800&h=600&fit=contain    → fits inside 800x600
?w=800&h=600&fit=pad&bg=ffffff  → contains + white padding

Gravity

When cropping (cover/crop mode), gravity controls which part of the image is kept.

Value	Description
center	Center of image (default)
top	Top edge
bottom	Bottom edge
left	Left edge
right	Right edge
top-left	Top-left corner
top-right	Top-right corner
bottom-left	Bottom-left corner
bottom-right	Bottom-right corner
auto	Saliency-based smart crop
face	Face detection smart crop

?w=400&h=400&fit=cover&g=top      → crop from the top
?w=400&h=400&fit=cover&g=auto     → smart crop (saliency)
?w=400&h=400&fit=cover&g=face     → smart crop (face detection)

See Smart Crop for details on auto and face modes.

Background color

Used with fit=pad to set the padding color.

?w=800&h=600&fit=pad&bg=ffffff    → white padding
?w=800&h=600&fit=pad&bg=000000    → black padding
?w=800&h=600&fit=pad&bg=f5f5f5    → light gray padding

The bg value is a 6-character hex color without the #.

Dimension bucketing

Spronta snaps requested dimensions to perceptual buckets (~5% geometric spacing). This means w=800 and w=812 produce the same cached variant, improving cache hit rates without visible quality difference.