基於瀏覽器的免費圖像轉換
PNG 到 JPG 轉換器
ImageConver converts a PNG into an opaque JPG in the browser by drawing the PNG onto a canvas, compositing transparent pixels over a selected background, and requesting image/jpeg output. PNG is lossless in its format specification and can carry optional alpha, while JPG is normally lossy and has no alpha channel. The result may be smaller for a detailed photo, but output size is not guaranteed to shrink. Your image contents stay in the browser and are not uploaded.
免費瀏覽器工具
Convert and inspect the JPG output
選擇一張圖像，選擇相關設置，並在下載前比較結果。圖像內容保留在此瀏覽器工作流程中。
一目了然
Quick facts for PNG to JPG conversion
- 輸入 MIME
- 圖片/png。
- Input extension
- .png; a file extension does not repair a damaged or mislabeled file.
- PNG壓縮
- PNG is lossless in the format specification, so encoding does not intentionally discard image detail in the way JPEG does.
- PNG alpha
- PNG supports optional alpha transparency. Fully or partially transparent pixels need a background before JPG encoding.
- 輸出 MIME
- 影像/jpeg。
- Output transparency
- JPG is opaque and cannot retain the PNG alpha channel.
- 卡通
- Standard PNG is not an animation-preserving target for this tool; the page converts one decoded raster image.
工作流程
How to convert PNG to JPG
- 1
Select the PNG
Choose a PNG that the browser can decode. Review whether it is a photo, screenshot, line art, logo, or transparent asset because each responds differently to JPEG encoding.
- 2
Choose the background
Set the compositing color before encoding. White is common for documents, but a page color or product backdrop may avoid a visible halo around semi-transparent edges.
- 3
Tune and compare quality
Adjust the requested quality, then inspect text, diagonals, gradients, and photographic texture. Do not infer quality from the slider alone.
- 4
Download and test the JPG
Open the saved file in the destination app or browser. Confirm that the background, dimensions, file size, and visual sharpness match the publishing requirement.
Controls
PNG to JPG settings explained
- 背景顏色
- This is the color beneath PNG transparency during compositing. It affects both fully transparent regions and the blended edge pixels around a partially transparent object.
- JPEG quality
- The value is passed as a quality request for a lossy image type. Higher values often preserve more detail and use more bytes, but browser encoders do not promise a fixed file size.
- Canvas dimensions
- The output keeps the decoded PNG dimensions unless the browser must reject or scale an oversized canvas. Very large artwork should be tested in the target browser.
- Canvas encoding request
- Canvas toBlob accepts an output MIME and a quality argument for lossy image types such as JPEG. Test the encoded result instead of assuming that a requested quality predicts the final file.
Output behavior
What PNG loses when it becomes JPG
Alpha is composited
PNG can store alpha values. JPG cannot, so the browser composites the PNG over the selected background before it asks the canvas for image/jpeg. A checkerboard preview is not part of the saved JPG.
Lossless detail can become lossy detail
PNG is lossless in the format specification, while JPG is normally lossy. Sharp text, one-pixel lines, and flat color boundaries can show ringing or block artifacts after conversion.
File size may move in either direction
A photographic PNG often contains redundant data and may become smaller as JPG, but a small flat-color PNG can already be efficient. Dimensions, texture, quality, and encoder behavior decide the result.
Metadata is not a safe assumption
Rendering through canvas can omit source metadata. If the PNG carries workflow notes or embedded information that must survive, preserve the original and verify the JPG independently.
決策指南
When PNG to JPG is a good fit
Use this conversion for a photo or graphic that needs broad JPG compatibility and does not need transparency. It can also make a transparent PNG usable in a system that requires a flat background, provided you deliberately choose that background first.
Keep PNG for screenshots, UI captures, logos, line art, and graphics with crisp edges or alpha. Converting solely to reduce bytes can disappoint: output size is not guaranteed to shrink, and a lower-quality JPEG may look worse without delivering a meaningful size advantage.
比較
Photo, screenshot, or line art?
| 來源 | PNGBehavior | JPGDecision |
|---|---|---|
| 照片 | May be large because the image has many colors and textures. | Often a reasonable JPG candidate; compare detail and output size at the target quality. |
| Screenshot | Keeps text and UI edges crisp with lossless encoding. | Keep PNG when small text, icons, or sharp borders are important. |
| Line art or logo | Can preserve flat colors and alpha edges cleanly. | Flatten only when an opaque background is acceptable; inspect halos and ringing. |
| Transparent product graphic | Stores the cutout edge with alpha. | Choose the final background first; JPG cannot carry the cutout itself. |
解決問題
Troubleshooting PNG to JPG output
The PNG cannot be selected or decoded
可能的原因： The file may be damaged, mislabeled, or outside the browser decoder path.
怎麼辦： Open and re-export it as a standard PNG, confirm the extension and MIME, then retry. A renamed file is not automatically a valid PNG.
Transparent areas have the wrong color
可能的原因： The alpha channel was composited onto the chosen background.
怎麼辦： Pick the background that matches the destination before conversion. There is no transparent JPG output to recover afterward.
A logo has a light or dark fringe
可能的原因： Semi-transparent antialiasing was blended with a background that differs from the final page.
怎麼辦： Use the actual display background, inspect at 100 percent, or keep the asset as PNG with alpha.
The JPG is larger than the PNG
可能的原因： PNG can be efficient for flat graphics, and JPEG size depends on dimensions, detail, quality, and browser encoder behavior.
怎麼辦： Compare both files at the same dimensions and visual threshold. Keep the smaller format only when its appearance is acceptable.
隱私
Browser-local PNG processing
The source image stays in your browser while the PNG is decoded, composited, and encoded locally. The page may load its own scripts, fonts, or other normal site assets, but this converter does not upload image contents to a remote conversion service.
Local processing reduces the need to send the image file elsewhere, but it does not replace normal device and browser privacy practices. Use a trusted device, review downloads, and retain the original PNG when it is the authoritative asset.
- 來源處理
- Image contents remain in the browser during the conversion flow.
- Transparency handling
- Alpha is composited locally onto the selected background before JPEG encoding.
常見問題
PNG to JPG questions
Is PNG lossless?
PNG is lossless in the format specification, so converting it to normally lossy JPG can change fine detail even when the dimensions stay the same.
Does PNG alpha survive in JPG?
No. JPG does not support alpha transparency. The PNG is composited over the selected background before the opaque JPG is encoded.
Will the JPG always be smaller?
No. Photos may shrink, but simple graphics or already efficient PNGs can stay similar or become larger depending on quality and encoder behavior.
Should I convert a screenshot to JPG?
Usually keep PNG when readable text, icons, and sharp UI edges matter. Test a JPG at the final display size if the destination requires it.
Can I choose the background for transparency?
Yes. Select the color that should appear beneath transparent and semi-transparent pixels before the JPG is created.
Does conversion preserve PNG metadata?
Do not assume it does. Canvas output can omit source metadata, so preserve the original if embedded information matters.
Is the PNG uploaded?
儘管頁面可以載入自己的腳本和資源，但轉換會將圖像內容保留在瀏覽器中，並且不會上傳到轉換伺服器。
參考