Why is my image still too big after compressing
Tools Nimbus is a free, no-signup developer toolkit that runs entirely in your browser, so your data is never uploaded to a server. An image that is still too big after compressing almost always has too many pixels. Quality settings shave bytes off an existing encode; pixel dimensions set the ceiling. Halve the width and height first, then re-encode with the Tools Nimbus Image Compressor.
Last updated September 2026
Pixels set the floor, quality only moves you toward it
A JPEG encoder works through the image in blocks, and the number of blocks is fixed by the pixel dimensions. Quality controls how coarsely each block is described, but there is a practical limit to how few bytes a block can take before it turns visibly blocky. So the file size you can reach is bounded from below by the pixel count, and the quality slider only moves you between that floor and the original size.
This is why resizing is so much more effective than re-compressing. Halving both the width and the height removes three quarters of the pixels, and the file size falls by roughly the same proportion at the same quality. Dropping quality from 90 to 75 might save 40 percent. Dropping it from 75 to 60 saves much less and starts to show. There is no quality setting that turns a 12 megapixel photograph into a 50 KB file without wrecking it.
Symptoms, causes and fixes
| Symptom | Most likely cause | Fix |
|---|---|---|
| Output is larger than the input | Re-encoding an already-compressed JPEG at a higher quality | Keep the original, or re-encode below its original quality |
| PNG does not shrink at all | PNG is lossless, so a quality slider has nothing to act on | Convert photographs to JPEG; reduce flat art to an indexed palette |
| Phone photo still around 2 MB | 12 megapixels, not the quality setting | Resize to the dimensions it will be displayed at |
| Screenshot is several megabytes | A high-density capture is two or three times the logical size | Scale back to one times, and use JPEG if it contains a photograph |
| Cannot hit a 50 KB or 100 KB cap | The target sits below the floor the dimensions allow | Resize first, then lower quality in steps |
| Transparent areas came out black | JPEG has no alpha channel | Stay on PNG or WebP, or flatten onto a chosen background |
| Blocky before it is small enough | Quality pushed far down on a detailed image | Trade dimensions instead of quality |
| Second pass saves almost nothing | Generation loss: the detail that compresses badly is already gone | Go back to the original and export once at the size you need |
What size is actually reachable
These are typical JPEG sizes for photographic content at a normal quality setting of around 75. They vary a great deal with subject matter, because a plain sky compresses far better than foliage or gravel, so treat them as a starting point rather than a promise.
- 4032 by 3024 (12 MP, a typical phone photo): roughly 1.5 MB to 3 MB
- 2048 by 1536 (3 MP): roughly 400 KB to 800 KB
- 1600 by 1200 (2 MP): roughly 250 KB to 500 KB
- 1024 by 768 (0.8 MP): roughly 100 KB to 200 KB
- 800 by 600 (0.5 MP): roughly 60 KB to 120 KB
Read that list backwards when you have a hard limit. A form that caps uploads at 100 KB is asking for something around 1024 pixels wide, not for a heroic quality setting on a full-resolution photo.
Why a second compression pass barely helps
JPEG is lossy, and the loss happens once. The first encode quantizes the frequency coefficients of each block and throws away what it judges you will not notice. Feeding that result back in at the same quality re-quantizes numbers that have already been rounded, so you pay another generation of softness and ringing for a saving that is usually in the low single-digit percentages.
The practical rule is to always export from the original. If you need a thumbnail, a web image and an email attachment, produce all three from the source file rather than compressing the compressed version each time. The same applies across formats: converting a lossy WebP to PNG does not restore anything, it just stores the already-degraded result losslessly and at a larger size. That trap is covered in why is my WebP image not opening.
PNG is a different problem
PNG is lossless. It applies a reversible per-row filter and then DEFLATE compression, and that is the whole story, so there is no quality knob to turn down and a compressor that offers one cannot do anything useful to it. A photograph stored as PNG is commonly three to ten times the size of a comparable JPEG, and no amount of re-saving will change that.
There are only three real levers on a PNG. Convert it, if the content is photographic and you do not need transparency. Reduce the color count, if it is a logo, chart, icon or flat illustration, since an indexed 8-bit PNG of 256 colors is often 60 to 70 percent smaller than the 24-bit version and usually looks identical. Or cut the dimensions. If you are weighing the format choice itself, read JPG vs PNG first, because picking the wrong one is what creates most oversized images in the first place.
What our compressor does, and what it does not
The Tools Nimbus Image Compressor decodes your file in the browser, re-encodes it as a JPEG at the quality you choose, and shows the original and compressed sizes side by side. Nothing is uploaded, so it works on a private screenshot or a client photo without the file leaving your machine. Being clear about the limits matters more than the pitch, though:
- It does not resize. The output keeps the original pixel dimensions. When dimensions are your problem, and they usually are, scale the image down in Preview, Photos, your phone gallery or an editor first, then run the smaller version through the compressor.
- The output is always JPEG. That is what makes photographs shrink, and it is also why a small flat PNG can come out larger. If the before and after numbers tell you the file grew, keep the original.
- Transparency is lost. JPEG has no alpha channel, so transparent regions are written out as solid black. Keep the PNG, or use the Image Format Converter to move to WebP, which supports transparency and is usually smaller than both.
A checklist
- Check the pixel dimensions before touching any quality setting.
- Decide the size the image will actually be displayed at and resize to it.
- Use JPEG or WebP for photographs, PNG only for flat graphics and text.
- Re-encode once, from the original, at the first quality that meets the limit.
- Compare the before and after sizes, and keep the original if it grew.
- For flat art, reduce the palette instead of reaching for a lossy format.
- Keep transparency in mind before converting anything to JPEG.
- Never generate a new size from a previously compressed export.
For the format decision behind most of these fixes, see JPG vs PNG, and for the format that keeps causing compatibility surprises see why is my WebP image not opening. All of our Tools Nimbus guides are indexed on one page.