Image Canvas Extender
Add custom margins and background around an image
Image Canvas Extender — what it does
Add margin around an image on any side independently — top, right, bottom, left — filled with a colour you pick or left transparent. The picture itself is untouched; only the canvas grows, which is how you meet a required aspect ratio without cropping anything out of the frame.
When this tool helps
- Padding a photo to a square canvas for platforms that crop non-square uploads.
- Adding space at the bottom of an image for a caption or logo bar.
- Creating breathing room around artwork before printing or framing.
How to use it
- Choose the image.
- Set the top, right, bottom and left margins.
- Pick a background colour, or select transparent.
- Process and download the extended image.
Accuracy, limits, and good practice
- Extending is the non-destructive alternative to cropping: to reach 1:1 you add space rather than cutting the subject's head off.
- Transparency requires PNG output; a JPEG will fill transparent margins with solid colour.
- Uneven margins shift the visual centre deliberately — useful when text will sit in the added space.
- Extending is often better than cropping for a thumbnail: padding keeps the whole composition visible where a square crop would cut the subject.
Frequently asked questions
How do I make an image exactly square?
Compute the difference between width and height, then split it across the two opposite margins to keep the subject centred.
Does this change the image resolution?
The original pixels stay as they are; the canvas around them grows, so the file's overall dimensions increase.
Can I extend by a percentage?
Margins are set in pixels. Work out the pixel value from the source dimensions first if you are thinking in percentages.
Does the added margin affect print size?
Yes, the image grows in pixels, so recalculate the print dimensions with the print size calculator if the output is for paper.
Related tools on this site
- Image Opacity Tool — Adjust image transparency and export as PNG
- Sprite Sheet Generator — Arrange multiple images into a downloadable PNG sprite sheet
- Favicon PNG Generator — Create common favicon and app icon PNG sizes from one image
Everything above runs inside this page. Image Canvas Extender needs no account, no upload, and no server round trip — close the tab and nothing is left behind.
圖片畫布擴展能做什麼
為圖片四邊分別加上邊距——上、右、下、左各自獨立——並填入你選的顏色或保持透明。畫面本身完全不動，只有畫布變大，這正是在不裁掉任何內容的前提下滿足指定比例的做法。
什麼時候用得上
- 把照片補成方形，以應付會裁切非方形上傳的平台。
- 在圖片下方留出空間，放說明文字或商標條。
- 在列印或裱框前，替作品四周留出呼吸空間。
使用步驟
- 選擇圖片。
- 設定上、右、下、左的邊距。
- 選擇背景色，或選擇透明。
- 執行處理並下載擴展後的圖片。
精確度、限制與實務建議
- 擴展畫布是裁切的非破壞性替代方案：要做成 1:1，是加空間，而不是把人物的頭切掉。
- 需要透明就必須輸出 PNG；JPEG 會把透明邊距填成實色。
- 不對稱的邊距會刻意位移視覺中心——當文字要放在新增空間時很好用。
- 做縮圖時擴展往往勝過裁切：補白能保住完整構圖，方形裁切則會把主體切掉。
常見問題
怎麼把圖片變成正方形？
先算出寬高差，再平均分配到相對的兩邊，主體才會維持置中。
這會改變圖片解析度嗎？
原始像素維持不變，只是外圍畫布變大，所以檔案整體尺寸會增加。
可以用百分比擴展嗎？
邊距以像素設定。若你習慣用百分比，請先依原圖尺寸換算成像素值。
新增的邊距會影響列印尺寸嗎？
會，圖片像素變多了。若輸出要印出來，請用列印尺寸計算器重算實際尺寸。
本站相關工具
- 圖片透明度調整 — 調整圖片透明度並輸出 PNG
- 圖片精靈圖生成器 — 將多張圖片排列成可下載的 PNG 精靈圖
- Favicon PNG 產生器 — 由一張圖片產生常用網站與 App 圖示尺寸
以上步驟全部在這個頁面內完成，圖片畫布擴展 不需要註冊、不上傳檔案、也不經過伺服器，關閉分頁後不會留下任何資料。