First separate pixels from file size
A width of 1200 px and a height of 800 px are pixel dimensions; they determine how much detail an image can show on a web page or in a document. 500 KB and 2 MB are byte sizes; they affect upload limits and loading cost. The two are related, but they are not the same thing: a very large solid-color image may not be large in bytes, while a smaller photo with complex texture may still be heavy.
If a platform asks for an “avatar 300×300 pixels,” you need to change pixel dimensions. If it asks for “under 200 KB,” you need compression or lower quality. Mixing these goals usually produces one of two results: the dimensions pass but the file is still too large, or the file becomes smaller but no longer fits the placement.
Aspect ratio prevents distortion
An image gets squashed or stretched when the new width-to-height ratio differs from the original. An original 1600×1000 image has a ratio of 1.6; forcing it to export as 1000×1000 will squeeze it horizontally or stretch it vertically. To avoid that distortion, lock the aspect ratio and enter only the width or the height, letting the other side be calculated from the original ratio.
LocalTools’ image resizer reads the original pixels. When aspect-ratio lock is on, changing the width calculates the height with it, and changing the height calculates the width with it. It processes one image at a time and exports PNG, JPEG, or WebP. When you are ready to resize, upload the image in the tool and confirm its original dimensions first.
Tradeoffs when width and height must be fixed
Some cases really do require a fixed canvas, such as a 1200×628 sharing image. If the source has a different ratio, resizing alone cannot both avoid distortion and preserve the whole picture. You need to choose one of three outcomes: keep the ratio and accept padding, crop the edges, or accept stretching. The current resize tool only redraws pixels; it does not crop, compose intelligently, or add borders, so it fits tasks where the ratio already matches or where proportional scaling is acceptable.
Shrinking usually reduces the pixel count, but it does not guarantee a smaller file. Enlarging only resamples onto more pixels; it will not restore detail that was never in the original. DPI metadata is not the control here either. Web pages and most forms care mainly about pixels and bytes, not print density on paper.
- To keep the full image: lock the ratio first and accept that the target width and height may not be fully fixed.
- To fit a fixed placement: crop first or design padding, then adjust the pixels.
- To satisfy an upload KB limit: still check the real file size after resizing.
How to choose the export format
PNG suits line art, screenshots, and graphics with transparent edges, but files may be larger. JPEG suits ordinary photos, but transparency is lost. WebP is often used for web images, but whether it can be opened or uploaded depends on the target system. The resize tool’s quality slider only matters for lossy exports such as JPEG and WebP; PNG is not compressed with that kind of quality slider.
If you only want to change the format without changing pixel dimensions, use the format converter. If the file is still too large after resizing, using the regular image compressor on JPEG output is more direct.
Hypothetical example
Suppose you have a 2400×1600 product photo for an article body that requires a width of 1200 px. The original ratio is 3:2. If you enter only width 1200 with the ratio locked, the height becomes 800 and the image is not stretched. If the article template requires 1200×900, that ratio is 4:3; changing directly to 1200×900 will distort the image. A steadier approach is to crop to 4:3 in an editor first, then export.
If the platform also requires the file to be below a certain KB value, resizing is only the first step. After export, check the actual byte size; if it is over the limit, lower JPEG/WebP quality or use the target KB compression flow. But target KB compression may continue scaling the pixel dimensions proportionally, so it is not suitable as the only final step when exact width and height must be preserved. After target compression, check the output dimensions and file size again. These numbers only show the method; they do not represent any fixed compression result.
With the ratio locked, enter width 1200 to get 1200×800. If you force 1200×900, the ratio changes and the image will stretch unless you crop or pad first.
Limits to know in advance
The tool depends on whether the browser can decode the input image, and it outputs a static result through canvas. Animated GIF or animated WebP will not keep animation; EXIF, ICC color profiles, and other metadata should not be expected to remain. It is also not a batch processor, DPI editor, ID-photo layout tool, or AI sharpening tool.
FAQ
- If I set only the width, can the height follow automatically?
- Yes. When aspect-ratio lock is on, entering a width calculates the height from the original image ratio. If the ratio lock is off, the result may be stretched.
- Can changing pixel dimensions guarantee the image is under a certain KB value?
- No. Fewer pixels often helps, but the final byte size is still affected by format, quality, image content, and the browser encoder.
- Will changing DPI make web images clearer?
- Web display mainly depends on pixel dimensions and CSS display size. The current tool does not edit DPI metadata and does not perform AI upscaling.
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