RAON image field guide
Compression, resize, and crop solve different problems
Compression changes how efficiently an image is stored. Resizing changes its pixel dimensions. Cropping removes part of the picture. All three can reduce file size, but only one may match the error shown by an upload form.
Choose the tool from the error
- “Maximum 5 MB”: compress first if the dimensions are already appropriate.
- “Maximum width 1600 px”: resize; compression alone does not change width.
- “Must be square”: crop in an editor; ordinary resizing should not remove content.
- Camera photo for a web page: resize to the display need, then compress once.
- Logo with transparency: keep PNG or WebP; JPG removes transparency.
What each action changes
| Action | Pixel width and height | Visible content | Typical use |
|---|---|---|---|
| Compress | Stays the same | Stays framed the same; fine detail may change | Meet a file-size limit |
| Resize | Changes | Whole image remains when aspect ratio is kept | Meet a dimension limit or avoid oversized web images |
| Crop | Usually changes | Edges or selected areas are removed | Create a new composition or aspect ratio |
| Convert format | Usually stays the same | May lose transparency or animation | Compatibility with an app, form, or browser |
RAON Tools resize keeps aspect ratio by default and does not crop. If you enter a new width, the height is calculated so the full picture remains visible. Turning off ratio lock can stretch the image; it still does not select and remove an area.
Why resizing also reduces memory
A 4000 × 3000 photo contains 12,000,000 pixels. When a browser canvas expands that image to RGBA data, a simple estimate is four bytes per pixel: about 48 MB before extra working copies and browser overhead. The JPG on disk might be only 4 MB, but processing can use much more memory.
| Dimensions | Pixel count | Approx. RGBA pixel memory | Relative pixels |
|---|---|---|---|
| 4000 × 3000 | 12.0 million | 48.0 MB | 100% |
| 2400 × 1800 | 4.32 million | 17.28 MB | 36% |
| 1600 × 1200 | 1.92 million | 7.68 MB | 16% |
| 1200 × 900 | 1.08 million | 4.32 MB | 9% |
The memory column is a planning estimate of width × height × 4 bytes. Real browser use is higher because decoding, canvases, previews, and export blobs can coexist temporarily.
A repeatable image preparation workflow
- Duplicate the source. Keep the original photo, especially when it contains metadata or may be edited later.
- Read the destination rules. Note format, maximum bytes, maximum width/height, required aspect ratio, and transparency needs.
- Resize only when dimensions are excessive. Keep aspect ratio unless distortion is intentional.
- Choose the format. Use JPG for ordinary photographs, PNG for transparency and crisp interface graphics, and WebP when the destination supports it.
- Compress once. Start near 80% for a JPG photo, then compare the result at 100% view rather than repeatedly re-saving the same export.
- Open the downloaded result. Confirm dimensions, file size, orientation, transparency, and readable text.
Examples based on the destination
Government, school, or application form
Follow the form exactly. If it accepts JPG under 2 MB with no dimension rule, compress a JPG copy. If it also requires 1200 × 1600 pixels, resize with the correct orientation first. Keep the original because forms sometimes request a different copy later.
Blog or website image
Do not upload a 4000-pixel camera photo into a 900-pixel content column. Resize near the largest display width, then compress. This reduces network transfer and browser decoding work for visitors. Check text and faces after export because those areas reveal damage quickly.
Screenshot or graphic
PNG often keeps small text and flat shapes crisp. JPG can introduce halos around letters and interface lines. If the screenshot is photographic and very large, WebP may be a useful compromise when the publishing system accepts it.
RAON image quality check
- Compare at the same displayed size. A smaller preview can hide artifacts.
- Inspect edges and text. Look for halos, block patterns, and softened lettering.
- Inspect gradients and dark areas. These can show banding after heavy compression.
- Confirm the whole frame. Verify that resizing did not stretch the image and that another app did not crop it.
- Check file properties. Confirm width, height, format, and bytes meet the destination rule.
There is no universal quality percentage. A detailed foliage photo and a clean portrait can produce different file sizes at the same JPG setting.
한국어 핵심 정리
이미지 압축은 가로·세로 픽셀을 유지하면서 저장 용량을 줄이고, 리사이즈는 픽셀 크기 자체를 바꿉니다. 크롭은 사진 일부를 잘라내는 별도 작업입니다. RAON Tools 리사이즈는 기본적으로 비율을 유지하므로 사진을 자르지 않습니다.
업로드 오류가 용량 제한이면 압축을, 가로·세로 제한이면 리사이즈를 사용하세요. 카메라 사진을 웹에 올릴 때는 필요한 크기로 먼저 줄이고 한 번만 압축하는 것이 좋습니다. 결과의 글자, 가장자리, 얼굴, 전체 구도를 확인한 뒤 사용하세요.