Format conversion helpers

Low-level helpers used by convertToJPEG and format selection.

Signature

interface ConversionOptions {
  backgroundColor?: string  // default '#ffffff' when flattening alpha
}

function convertFormat(
  image: HTMLImageElement | HTMLCanvasElement,
  targetFormat: string,
  options?: ConversionOptions
): Promise<HTMLCanvasElement>

function detectTransparency(
  image: HTMLImageElement | HTMLCanvasElement
): Promise<boolean>

function shouldConvertToJPEG(
  currentFormat: string,
  hasTransparency: boolean,
  fileSize: number
): boolean

shouldConvertToJPEG returns true for large opaque PNGs (roughly > 500KB) where JPEG is likely smaller.

Via compress

await compress(pngFile, {
  convertToJPEG: true,
  quality: 0.85,
})

Related

• Guide: Format conversion