Start with the requirement
An upload form may ask for an image below 200 KB, 500 KB or 1 MB. That is a file-size limit, not a pixel dimension. Two photos with identical dimensions can encode to very different sizes because detail, noise and transparency affect compression.
Keep the original file. Decide whether the receiving service accepts JPEG or WebP, and whether it also sets a width or height requirement. Photobox uses 1024 bytes per KB in its size controls. A service using decimal units may count the same file differently, so leave a little room below a strict limit.
Use target-size compression
Open Image Compression and select one or more static JPEG, PNG or WebP files. The output format controls the available compression settings. Choose JPEG or WebP for target mode; PNG uses lossless re-encoding and has no quality target.
- Choose the accepted output format. JPEG needs a background color if the source has transparent areas.
- Switch from Quality to Target size. Enter the limit and choose KB or MB.
- Generate the images. Read the actual size for each result and check the encoded preview before downloading.
- For a batch, select the results you want and download the ZIP. A failed file does not cancel the successful ones.
Understand an unreachable target
Photobox tries at most eight quality values between 10% and 95%. It keeps the highest tested quality that satisfies the target. This is a bounded search, so it does not promise the exact requested byte count or the mathematically best possible encoding.
If even the lowest quality attempt is too large, the tool reports that the target was not reached and shows the smallest attempted result. It does not silently shrink the image. An already optimized file can also become larger after re-encoding, particularly when converting a small source to PNG.
Reduce dimensions when quality is not enough
Send a generated result to Resize Image, or reopen the original there when preserving quality is more important than saving an intermediate step. Keep the aspect ratio locked and reduce the width or percentage. Then continue to Image Compression and test the target again.
For example, reducing a 2400 × 1600 image to 1200 × 800 keeps one quarter of the pixels. The encoded file will not necessarily be exactly one quarter as large. Fine detail, the chosen format and the quality setting still matter. Crop unnecessary edges before resizing when they do not belong in the final image.
Check the file you will actually send
Inspect text, faces, gradients and thin edges in the saved image. Confirm its dimensions, format and file size against the upload form. Download acts on the generated copy; the original input stays separate. Pixel-processing outputs do not copy the source EXIF/GPS, while the dedicated EXIF editor follows its own metadata-preservation rules.