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We recommend separating the aspect ratio and resolution into two parameters: 
{
  "size": "16:9",
  "resolution": "2k"
}
You can also pass exact pixel dimensions: 
{
  "size": "3840x2160"
}
  • Aspect ratios: 1:1, 3:2, 2:3, 4:3, 3:4, 16:9, 9:16, 21:9, 9:21.
  • Resolutions: 1k, 2k, 4k.
  • Defaults: size=1:1, resolution=2k.
  • Expose exact WxH pixels only in an advanced mode.

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Resolution fields

We recommend using only resolution. The following aliases are also supported:
FieldExampleDescription
resolution1k / 2k / 4kRecommended field.
image_size2kCompatibility alias.
scale4kCompatibility alias.
upscale2k / 4kCompatibility alias.
quality2k / 4kLegacy compatibility; no longer recommended for expressing resolution.

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Dimension mapping

When size is an aspect ratio, the service maps it to exact pixel dimensions. Width and height are aligned to 16 pixels. The 4K tier stays within an approximate 3840x2160 pixel budget, so square 4K output is 2880x2880, not 3840x3840.
size1K2K4K
auto / 1:11024x10242048x20482880x2880
3:21008x6722016x13443504x2336
2:3672x10081344x20162336x3504
4:31024x7682048x15363264x2448
3:4768x10241536x20482448x3264
5:4960x7682000x16003200x2560
4:5768x9601600x20002560x3200
16:91024x5762048x11523840x2160
9:16576x10241152x20482160x3840
2:11024x5122048x10243840x1920
1:2512x10241024x20481920x3840
21:91008x4322016x8643696x1584
9:21432x1008864x20161584x3696

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Images per request

The maximum n depends on the resolution tier:
TierMaximum n per requestTypical time
1k1About 60 seconds
2k4About 120 seconds
4k4About 180 seconds

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Recommendations

  • Use 2k by default for the best balance in most products.
  • 4k takes longer to generate; expose it under advanced options.
  • 1k can generate only one image per request and is suitable for previews or low-cost batches.
  • If users care only about social-media formats, show aspect ratios first instead of asking them to enter pixels.