“Too large” can describe three different problems: a website rejects the file's byte size, the screenshot has excessive pixel dimensions, or the browser cannot finish processing it. Identify which limit you hit before changing the file extension. The lightingshot editor can crop an accepted image and export PNG or JPEG, but it does not provide a target-size compressor or a resize field.
Identify the limit first
| What happens | What to check | Useful next step |
|---|---|---|
| An attachment form rejects a saved file | The destination's stated file-size and format rules | Remove irrelevant image area, compare PNG and JPEG, then check the actual saved size |
| Lightingshot rejects the import | Source file bytes, width, height, and total pixels | Create a smaller source before importing |
| Import works but export fails or stalls | Image dimensions and available device resources | Keep an original copy and retry with a smaller relevant region |
Read the destination's own message. A form that accepts only one format will not be fixed by producing a smaller file in an unsupported format. Do not assume a universal attachment limit; different services set their own rules.
Reduce the area that is not needed
For an accepted image, start with content rather than compression. A wide sidebar, empty margin, or unrelated browser window can occupy many pixels without helping the recipient. Choose 裁剪 (Crop), drag around the useful section, and release to apply. Keep chart axes, labels, or the error context that the explanation depends on.
Cropping removes pixels outside the selection; it does not squeeze all the original content into a smaller image. This is useful when you need one table row from a long dashboard. It is less useful when the recipient truly needs the entire document. In that case, consider several clearly named captures or an export provided by the original application.
Use 撤销 (Undo) if the crop removes something important. Export a separate copy so your original remains available. See the crop workflow for how existing annotations interact with cropping.
Compare actual PNG and JPEG files
Open 导出图片 (Export image), choose a format, and select 下载文件 ↓ (Download file). Compare the saved files using your device's file information. PNG preserves image detail without lossy encoding; JPEG may suit photo-heavy content but can introduce artifacts around small text. A different format does not guarantee a smaller file for every screenshot. MDN describes the format tradeoffs.
Lightingshot currently uses a fixed JPEG quality setting. There is no quality slider, preset such as “under 1 MB,” or promised percentage reduction. The browser's canvas encoder accepts a quality parameter for formats such as JPEG, as explained in the canvas export documentation; this release sets that value internally.
Inspect small labels after exporting. If JPEG makes the information unclear, keep PNG and reconsider the capture area or the delivery method. Repeatedly re-encoding a JPEG is not a reliable route to a readable target-size attachment.
Why zoom and PDF are not size controls
The plus, minus, and 适合窗口 (Fit to window) buttons change your editing view. They do not reduce canvas dimensions or the pixels that are exported. Seeing a smaller image on screen is not evidence that the saved attachment is smaller.
PDF exports contain JPEG image slices on A4 pages. That can be useful for document delivery, but it is not a guaranteed compression technique. It also changes how a tall image is presented. Use the format guide to choose a delivery format, then inspect both readability and the final file size.
If the original cannot be imported
The import checks reject files above 40 MB, images with either side above 32,000 pixels, or images above 80 million pixels in total. Those are different tests: a highly compressed file can have small byte size and still contain too many pixels. These limits are ceilings, not promises that every device will comfortably process every accepted image.
You cannot use the editor's crop tool on an image whose import has failed. Capture a shorter region at the source, use the original application's export controls, or prepare a smaller image with an appropriate local tool before importing. Avoid sending a sensitive original to an unfamiliar online compressor simply to work around the limit.
Check the final handoff
Keep the inspected copy, confirm its size against the recipient's stated requirement, and attach that exact file. A meaningful filename helps distinguish it from earlier attempts. For download or browser-memory failures, use the help checklist; a filename extension alone cannot repair a failed export.