“Resize without losing quality” sounds like a trick, but it is mostly a matter of knowing which direction you are going. Making a picture smaller is almost always safe. Making it bigger never is, however clever the software claims to be. Once you remember that single rule, most resizing questions answer themselves.
What resizing really does
A digital image is a grid of pixels. When you shrink it, the software combines groups of neighbouring pixels into one, so each remaining pixel carries the average of several originals. Done well, the result looks sharp, because there is plenty of information to draw from. When you enlarge a picture, the software has to invent pixels that never existed, by guessing from their neighbours. The guesses look smooth but soft, and fine detail cannot return.
Shrinking: where the real gains are
Most pictures that need resizing are too large, not too small. A 4000-pixel photo shown in a 800-pixel-wide blog column wastes bandwidth. Reducing it to 1600 pixels (twice the displayed width, so that high-density screens still look crisp) costs nothing visible and cuts the file size by about 80 percent. Think of the target as the size where the picture will be displayed, multiplied by two at most.
Enlarging: when it is unavoidable
Sometimes a form demands a minimum size and you only have a small picture. In that case enlarge it as little as possible, and accept that the result will look slightly soft. Never enlarge a picture several times in small steps, hoping each step will be tidy: the softness accumulates. One single, direct resize to the final size is always better than a chain of small ones.
Keep the proportions
If you change only the width or only the height, the picture stretches. Faces become wide and round, circles become ovals. Always lock the proportions, or fix one side and let the other follow. When a destination wants a different shape, such as a square from a landscape photo, use cropping to change the shape and resizing to change the size. These are two separate jobs, and mixing them is how pictures end up squashed.
Choosing a fit method
The Image Resizer offers several ways of fitting a picture into a target size:
- Crop to fill: the picture fills the whole frame, and the parts that do not fit are trimmed. Best for profile photos and social posts.
- Fit inside: the whole picture stays visible, and empty bars fill the leftover space. Best when nothing may be cut off, such as a document or a product shot.
- Stretch: forces the picture into the size and distorts it. I rarely recommend it, except for abstract backgrounds where distortion goes unnoticed.
Choose the output format wisely
Resizing and saving are two steps. After resizing, the picture is saved again, so a lossy format such as JPG gets one more round of compression. Use a high quality setting, around 90 percent, for the final save, particularly if you will resize again later. If the picture has text or transparency, keep it as PNG.
Resize in the right order
If your workflow includes cropping, adjusting and resizing, do the resize last. Edits done on a larger image keep more detail, and shrinking at the end gives the sharpest outcome. The exception is when you are working with very heavy files that slow your device down. In that case a first resize to a comfortable working size helps, as long as it is still larger than the final target.
An example you can follow
You have a 4032 x 3024 phone photo and need a 1200 x 800 image for a blog post. The shapes differ slightly, because the photo is 4:3 and the target is 3:2. First choose crop to fill, so the photo is trimmed a little at the top and bottom to match 3:2. Then scale it down to 1200 x 800. Save as JPG at 85 to 90 percent. The result is usually under 250 KB, down from several megabytes, and it looks crisp on every screen.
Batch resizing
If you have a whole folder of pictures for a product page or an album, resize them together. The tool can produce several sizes of every photo in one go, which saves a lot of time when you need a thumbnail, a medium and a large version for a website.
Mistakes worth avoiding
- Resizing the already-resized copy instead of going back to the original.
- Enlarging a thumbnail and expecting a sharp picture.
- Stretching a photo to fit a space instead of cropping.
- Saving at very low quality to get a smaller file, instead of reducing the pixel size.
- Forgetting to keep the original.
Treat resizing as a one-way trip: shrink from the original, shrink once, and keep the big file safe. Do that, and you will rarely see a soft or squashed picture.