Pixels describe the file. Proportions describe its shape.
An image that is 1,200 pixels wide and 800 pixels high has a 3:2 aspect ratio. Reducing it to 600 by 400 pixels keeps the same shape. Changing it to 600 by 600 changes the shape and stretches its content unless you crop instead.
Before resizing, find the actual dimensions needed by the destination. An upload field may specify width, height, aspect ratio and file size separately. Meeting one condition does not necessarily meet the others.
Keep the ratio locked for a faithful resize.
In the LAMPIF resizer, the ratio lock uses the source image’s dimensions. When you change the width, the height is recalculated. When you change the height, the width is recalculated. One-pixel rounding differences are normal because dimensions must be whole numbers.
For a proportional resize: new height = new width × original height ÷ original width. A 2,400 × 1,600 image resized to 1,200 pixels wide becomes 1,200 × 800.
Resizing and cropping solve different problems.
Resizing changes the dimensions of the entire image. Cropping changes which part of the image is included. If you need a square from a wide photograph, a crop is usually the way to preserve proportions.
The LAMPIF resizer does not crop. Prepare the crop in an image editor first, then use this tool to set the export dimensions. Turning off the ratio lock is useful only when changing the shape is intentional.
Bigger is not the same as more detailed.
Enlargement uses interpolation to create additional pixels from the available source. It cannot recover a texture or edge that was never captured. The result may look acceptable at a distance but soft at its displayed size.
Use the highest-quality original you have. Avoid enlarging a file, compressing it, then repeatedly resizing that export. Work from the original each time you need a new version.
Check the practical result.
After resizing, inspect the output at the size at which people will actually see it. Check embedded text, straight edges and small details. Then compare the file size with the destination’s limits.
When the dimensions are correct but the file is still too large, changing the encoding quality or output format may help. Dimensions and compression are separate controls.
Technical reference
MDN: Drawing and scaling images with canvas.
Questions about a tool? Visit the help center or contact support@lampif.com.