siyuan-note/siyuan · error

prepared image exceeds size limit

Error message

prepared image exceeds size limit: %d bytes

What it means

Thrown at kernel/util/openai.go:824 after the image is converted to JPEG at quality 92: if maxBytes is positive and the encoded JPEG still exceeds that byte budget, preparation fails with this message. The %d is the byte limit from configuration, not the actual encoded size.

Solutions

1. Increase the configured byte limit for AI image input
2. Lower the resize limits (maxEdge / maxPixels) so images shrink more aggressively before encoding
3. Pre-compress the image externally (e.g. quality 60 JPEG) and resend
4. Check what maxBytes value appears in the message and compare against the actual file size

Example fix

// before: no downscale, tight byte cap
img, err := prepareImage(bigPhoto, "image/jpeg", 0, 0, 100*1024)
// after: force downscale so re-encode fits the cap
img, err := prepareImage(bigPhoto, "image/jpeg", 2048*2048, 1568, 100*1024)

cfg, _, _ := image.DecodeConfig(bytes.NewReader(data))
if maxBytes > 0 {
    est := cfg.Width * cfg.Height * 3 / 10 // rough JPEG bytes estimate
    if est > maxBytes { return errors.New("image will exceed byte limit; downscale first") }
}

When it happens

Trigger: maxBytes is set and even the quality-92 JPEG re-encode of the (possibly resized) image is larger than maxBytes — typically huge photos where the pixel budget or max-edge resize was disabled or set too high.

Common situations: Users configure a very small byte limit (e.g. 100 KB) while sending large camera photos; callers pass maxBytes=0 for other paths but a strict limit here; resizing limits (maxEdge/maxPixels) set to 0 disable downsampling so nothing shrinks the payload.

Understand the failure class

Background: payload too large / request exceeds maximum size: why libraries cap bytes and how to fix oversize payloads — this error's family across 50 libraries.

Related errors

• generated image exceeds size limit
• image exceeds pixel limit
• BASE64_IMAGE_SIZE_LIMIT
• decode image failed
• encode image failed

AI-assisted analysis of siyuan-note/siyuan@9f775e8a12 (2026-09-19). Data as JSON: /api/errors/58bd30911a538665. Report an issue: GitHub.

Appendix: source

Thrown at kernel/util/openai.go:824

		if err = png.Encode(&output, decoded); err != nil {
			return PreparedImage{}, errors.New("encode image failed: " + err.Error())
		}
		if maxBytes <= 0 || output.Len() <= maxBytes {
			return PreparedImage{
				Data:       output.Bytes(),
				MIMEType:   "image/png",
				Width:      bounds.Dx(),
				Height:     bounds.Dy(),
				SourceSize: len(data),
			}, nil
		}
	}
	var output bytes.Buffer
	if err = jpeg.Encode(&output, decoded, &jpeg.Options{Quality: 92}); err != nil {
		return PreparedImage{}, errors.New("encode image failed: " + err.Error())
	}
	if maxBytes > 0 && output.Len() > maxBytes {
		return PreparedImage{}, fmt.Errorf("prepared image exceeds size limit: %d bytes", maxBytes)
	}
	return PreparedImage{
		Data:       output.Bytes(),
		MIMEType:   "image/jpeg",
		Width:      bounds.Dx(),
		Height:     bounds.Dy(),
		SourceSize: len(data),
	}, nil
}

// ValidateGeneratedImage 校验生成图片的格式、尺寸和体积。
func ValidateGeneratedImage(data []byte) (mimeType, extension string, err error) {
	if len(data) == 0 {
		return "", "", errors.New("generated image is empty")
	}
	if len(data) > maxGeneratedImageBytes {
		return "", "", errors.New("generated image exceeds size limit")
	}

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