internal/png/stdlibwriter.go
func (e *encoder) writeIDATs() {
	if e.err != nil {
		return
	}
	if e.bw == nil {
		e.bw = bufio.NewWriterSize(e, 1<<15)
	} else {
		e.bw.Reset(e)
	}
	e.err = e.writeImage(e.bw, e.m, e.cb, levelToZlib(e.enc.CompressionLevel))
	if e.err != nil {
		return
	}
	e.err = e.bw.Flush()
}
func (e *encoder) writeIDATs() {
	if e.err != nil {
		return
	}
	if e.bw == nil {
		e.bw = bufio.NewWriterSize(e, 1<<15)
	} else {
		e.bw.Reset(e)
	}
	e.err = e.writeImage(e.bw, e.m, e.cb, levelToZlib(e.enc.CompressionLevel))
	if e.err != nil {
		return
	}
	e.err = e.bw.Flush()
}
// Write the actual image data to one or more IDAT chunks.