Guide
画像リサイズ: what it does and how to use it
The image resizer changes pixel dimensions, either to an exact width and height or by a percentage of the original. That is the right first step when a form asks for 1200×630, a marketplace wants a square thumbnail, or a photo is simply larger than the page will ever display.
Pixel mode can lock the aspect ratio. With the lock on, typing a width updates the height so the picture is not stretched. Turn the lock off only when you truly want a different shape — stretching a portrait into a landscape will look wrong. Percent mode scales from 5% to 100%, which is useful when you want “about half the size” and do not care about an exact pixel count.
One image is processed at a time, in the browser. The download is a new file; the original is not overwritten. Resizing down is safe. Resizing up only spreads the same pixels across more space, so a small screenshot will look soft if you enlarge it.
How to use it
- 1
Drop a single image
The drop zone accepts a picture and reads its current dimensions so the width, height, and ratio start from the real file.
- 2
Pick pixels or percent
Pixels is for a target size such as 1920×1080. Percent is for a relative shrink, for example 50% of whatever the camera produced.
- 3
Set the size
In pixel mode, edit width and height. Leave “Lock aspect ratio” checked unless you mean to stretch. In percent mode, drag the scale. 100% is the original size; the slider does not enlarge past that.
- 4
Download the result
When resizing finishes, the row shows the new filename and file size. Download it and open it once at the size you will actually use.
Good uses
- Open Graph and social images that must be an exact pixel size.
- Shrinking phone photos before they go into a CMS.
- Making a lighter copy of a diagram without recompressing it by guesswork.
- Checking how a photo looks at half scale before you commit to that size.
Tips
- Decide the display size first. A hero image that is shown at 1600 pixels wide does not need a 6000-pixel source.
- Lock aspect ratio for photos of people and products. Unlock it only for assets that were designed to be cropped or stretched.
- Resize, then compress. Doing both in the right order avoids encoding a huge image just to shrink it afterward.
- Percent mode stops at 100%. To go larger than the original you would be inventing pixels — this tool does not do that.
Limits to know
- One image per run, not a folder.
- Percent scaling cannot go above 100% or below 5%.
- The tool changes dimensions. It does not crop, rotate, or add a background.
Questions
Will locking the ratio crop the image?+
No. The lock only keeps width and height in proportion. The full picture stays in frame; it is not cropped to a new shape.
Why can’t I make the image larger than the original?+
Enlarging a bitmap does not add real detail. Percent mode is capped at 100% so you do not accidentally publish a blurry upscale.
Does this upload my photo?+
No. The resize runs locally and the new file downloads to your device.
What if I need a square thumbnail?+
Turn the aspect lock off and set equal width and height only if stretching is acceptable. This tool does not crop to a square.