Compress BMP Bitmap Free Online Secure
A BMP keeps every pixel raw. This lowers the resolution and saves it as PNG — still lossless, far smaller.
Compress your file
Drop a BMP here, or choose one.
Your file never leaves this device. Everything runs in your browser.
Nothing uploaded
Two different ways of making a file smaller
There are only two ways to make a file smaller, and they are not alike. The first is to find repetition and write it down once instead of a thousand times — the method of zip, of PNG and of the streams inside a PDF. Nothing is lost; the original comes back bit for bit. The second is to decide that some of the information was not worth keeping, and this is what JPEG does with a photograph: it discards the detail the eye is least likely to miss. The first method has a hard limit, because there is only so much repetition to find. The second has no limit at all — you can go on discarding until nothing recognisable is left — which is why it comes with a quality setting and the first does not.
Where you need it
An attachment that will not fit the mail server's limit; a portal that rejects anything over a few megabytes; a website where every image is downloaded by every visitor; a phone running out of space; an archive of scans where the same document occupies ten times what it needs. Compression is almost always about somebody else's constraint rather than your own preference.
Questions people ask
How small can I go before it starts to look bad?
For photographs, surprisingly far. Dropping a JPEG to around three quarters of its original quality typically removes more than half the file and leaves nothing visible at normal viewing size. Below about half quality, edges start to show a faint halo and flat areas become blotchy, first in skies and skin. The honest test is to look at the result at full size before sending it, since the damage is invisible in a thumbnail and permanent once saved.
Why did compressing my PNG barely help?
Because it was probably already compressed, and because PNG never discards anything. The format finds repetition, and a photograph saved as a PNG has very little repetition to find, which is also why it was so large to begin with. If the image is a photograph, converting it to JPEG will shrink it enormously. If it is a screenshot, a logo or a diagram, it is already near the smallest it can be without losing something.
Does the file lose quality?
It depends on what the two formats can hold. Converting between formats that store the same thing — a PNG to a BMP, a WAV to a FLAC — loses nothing. Converting into a format that throws information away to save space, such as JPEG or MP3, loses a little every time, and converting back does not bring it back. Where a choice exists, this page errs towards keeping the original quality rather than making the smallest file.
Is my file uploaded anywhere?
No. The conversion happens inside your browser, on your own machine; the file never leaves it and there is no server here that could receive it. That is why a large file is limited by your own memory rather than by an upload, and why nothing you convert can appear in anybody's logs — including ours. The audio and video tools do fetch their conversion engine from this site the first time you use them, some thirty megabytes once; after that the work still happens entirely on your machine.
Why people compress BMP files
BMP is the oldest and simplest picture format in everyday use. It stores every pixel as it is, with no clever packing at all, which makes it easy for old software to read and enormous in size. A single screen-sized BMP can weigh five or ten megabytes; a scanned page at a good resolution can be more than thirty. Nobody wants to email a file like that, put it on a website or keep a hundred of them on a phone. That is why people look to compress BMP files: they want the picture without the bulk.
BMP files turn up in surprising places. Old scanners and screenshot tools save them. Legacy software, industrial equipment, medical and laboratory instruments and some embedded systems still produce them. Archives of older material are full of them. Whenever one of these files has to travel, be stored or be published, someone has to make it smaller, and that is the job of this page.
This page lets you compress BMP files entirely in your browser. The image never leaves your device, which matters for scans of documents, lab images and anything private. Below you will find how the size is reduced, why the result is a PNG rather than a BMP, what is preserved, and how to choose a setting.
What this tool does
It lowers the resolution
You pick a resolution, and the tool produces a picture with fewer pixels. Because a BMP stores every pixel without compression, its size follows the pixel count exactly: halve the width and height and the file becomes a quarter of the size. Reducing the resolution is therefore a very effective way to compress BMP files, and you remain in control of how much detail you keep.
It saves the result as PNG
The smaller picture is saved as a PNG. This is not a quirk but the whole point. A BMP does not compress at all, so a BMP at a lower resolution would still be as heavy per pixel as before. PNG, by contrast, compresses without losing anything, so it keeps every colour exactly and stores the picture in far less space. The output is a PNG because that is what makes the file small.
Why not stay in BMP?
Staying in BMP would mean staying the same size, because BMP does not compress at all. The only way to make a BMP smaller as a BMP is to remove pixels, and the file would still be large for what it holds. Moving to PNG gives you the saving from fewer pixels and the saving from lossless compression, which is how a huge BMP can become a small, clean PNG.
What is preserved
Every colour, exactly
When you compress BMP files here, every colour is kept exactly, because PNG is a lossless format. Nothing is approximated, smoothed or reduced to a smaller palette. A flat blue stays that blue; a gradient stays a gradient. The only thing that changes is how many pixels there are, and what remains is stored perfectly.
The dpi setting
A BMP carries a note in its header saying how many dots per inch it was meant to print at. This tool reads that value and carries it over to the PNG. The result is a picture that, if printed, takes up the same area as the original, with fewer dots. That matters for scans: a scanned page keeps its intended physical size, even though it now has fewer pixels.
Why the dpi is worth keeping
Without a dpi note, a program has to guess how large a picture is meant to be. Some guess a standard value and print it at the wrong size. By carrying over the dpi, the converted picture knows its intended size, so a scanned A4 page still prints as A4 when you place it in a document or send it to a printer.
What changes
The file type
The result is a PNG, not a BMP. If you need a BMP specifically, for instance for a legacy program that cannot read anything else, this tool is not the route: any BMP you made would be as large as the original at the same resolution. For nearly every modern purpose, a PNG is accepted everywhere and is the better choice.
Fewer pixels
Lowering the resolution means fewer dots describe the picture. Fine lines may become slightly softer and tiny text harder to read. At sensible settings you will hardly notice on a screen, but if your picture contains small text, check the result at the size it will be read.
Detail cannot be brought back
A higher setting cannot restore pixels that are gone. If you compress a BMP and later need the full detail, you must return to the original. So keep the original safe, and always compress from it.
What a BMP file is
BMP stands for bitmap. It is a format from the early days of personal computers, designed so that any program could read it with almost no effort: a short header that says how big the picture is, followed by the colour of every pixel, one after another. There is no compression and no clever coding. That simplicity is why BMP is still found in old software, in instruments and in archives, and why a BMP of even a modest picture is so large.
The arithmetic is easy. A picture of 2000 by 1500 pixels has three million pixels, and a BMP stores roughly three bytes for each, so the file is about nine megabytes, whatever the picture contains. A blank white page and a detailed photograph weigh the same. When you compress BMP files by converting them, the difference between the two shows up at once: the blank page shrinks to almost nothing, because PNG packs repetition very efficiently, while the photograph shrinks less.
Why the size depends only on the pixel count
Because a BMP does not look at what the picture shows, its size depends only on its dimensions. That is why lowering the resolution is such a clean way to compress BMP files: every pixel you remove takes its bytes away with it. And it is why the change of format helps as well: once PNG compresses the remaining pixels, flat areas collapse to a fraction of their original size.
Scans, screenshots and technical images
The pictures people compress as BMP files fall into a few groups, and each behaves differently. Scanned documents are mostly white with black text, which PNG compresses extremely well, so a huge scanned BMP can turn into a small PNG with no visible change. Screenshots, with flat colours and sharp text, behave in the same way. Technical and laboratory images, such as microscope pictures and instrument captures, hold more subtle variation and shrink less, though still dramatically compared with BMP.
Photographs saved as BMP shrink the least when you compress BMP files to PNG, because their millions of slightly different colours leave little to pack. For a photograph, the best route is to convert the resulting PNG to JPG afterwards, which gives a much lighter file at the price of a small loss of detail.
Choosing a resolution for scans
For scanned text, a resolution that makes the smallest letters clearly legible is enough. If the original was scanned at a very high resolution, you can often halve it without losing readability. Check by zooming in on the smallest text in the result; if it is crisp, you can compress BMP files from the same scanner at the same setting from then on.
Medical and laboratory images
If your BMPs are images where fine detail matters, such as measurements or diagnostic pictures, be conservative and keep the original at full resolution as the record. A reduced copy is for sharing and convenience; the original remains the evidence. Because the conversion is lossless in colour, nothing in the pixels that remain is altered, but pixels you drop are gone from the copy.
How to compress BMP files here
Add your image
Drop the BMP onto the page or pick it from your device. It is read inside your browser and is not uploaded.
Pick a resolution
Choose the setting that matches the use: a moderate one for an email or a form, one that matches the display width for a web page, a larger one if the picture will be printed.
Compress and compare
Press the button and download the PNG. Open it beside the original at the size you will use. If it looks right, you are done; if it looks too soft, repeat from the original with a higher setting.
Questions people ask before compressing
Why did I get a PNG instead of a BMP?
Because BMP does not compress. Saving as PNG is what makes the file small, and it is lossless, so every colour is kept exactly.
Will the picture look worse?
Only slightly, at sensible settings. Fewer pixels means less fine detail, but colours are exact and the result is clean.
Does the printed size change?
No. The dpi from the BMP header is carried over, so the picture keeps its intended physical size.
Is my image uploaded?
No. Everything runs in your browser and the image never leaves your device.
Who needs to compress BMP files
People with old scans and archives
Old scanners and archives of earlier material are full of BMPs. Converting them saves space and makes them usable on modern systems.
Users of legacy and technical equipment
Instruments and older software often output BMP. Compressing makes the images easy to send to colleagues and attach to reports.
Anyone short of storage
A folder of BMPs can reach gigabytes. Lossless PNG copies at a sensible resolution take a fraction of the space.
Common mistakes
Expecting a BMP back
The result is a PNG. If you need BMP, keep the original.
Deleting the original
You cannot restore pixels later. Keep the full-size file.
Choosing too small a size
A picture reduced too far loses legibility. Check the result at reading size.
Related tools
Once you have the PNG, compress PNG can shrink it further, and converting PNG to JPG gives a much lighter file for photographs. If a BMP is sideways, rotate the BMP first. To put the pictures in a document, use PNG to PDF, and for photos from a phone, compress JPG.
When to compress BMP files, and when not to
Compressing is right when a BMP has to be sent, stored or published, which is nearly always. It is the wrong move only when a program insists on BMP specifically, in which case keep the original and use it for that program. And it is pointless to compress BMP files you never move or open: if a picture sits untouched on a disk with plenty of room, there is no urgency, though converting still frees space.
For the common cases, such as emailing a scan, putting an image on a website, tidying an archive or sharing an instrument picture, it is quick, private and effective to compress BMP files in the browser. Your original is never changed, so you can come back and compress BMP files again at a different setting whenever you like.
Batches of BMP files
If you have many images to convert, compress BMP files one at a time and keep the originals in a separate folder. Use the same setting for all of them so that the results look consistent. Try one first and check it at the size you will use, so you do not have to redo twenty of them.
Going further after the PNG
Once you have the PNG, you have choices. If it is a document or a screenshot, keep it as it is: it is already small and exact. If it is a photograph, convert it to JPG for a much lighter file. If it is going into a document, place it in a PDF. Each of these steps starts from the clean, lossless PNG you made, so nothing is lost by taking them in order.
Large images and slow devices
Everything runs on your own device, so very large BMPs depend on its memory. A scan of a few thousand pixels on a side is no trouble for a modern computer. A huge image may be slow on an older phone. If it struggles, give the browser a moment and avoid switching to other apps while it works.
Why PNG is a safe destination
PNG is supported by every browser, every operating system and almost every program that handles pictures. It is lossless, so it is a safe place for an archive copy, and it is compact enough to send. If you ever need a BMP again, any image editor can make one from the PNG in a moment, at the cost of the size you saved.
Your image stays on your device
The compression happens locally. Your image is read by your own browser, reduced there and handed back. Nothing is uploaded, so there is no copy on a server and no one else who could see it. For scans and instrument images, that is the safe way to compress BMP files.
A worked example
Say you have a scanned form saved by an old scanner as a BMP of 2480 by 3508 pixels and 26 megabytes, and you need to email it. You drop it here, choose a resolution that brings it to about half the width and height, and press the button. You download a PNG of a few hundred kilobytes: colours exact, text legible and the printed size still A4. You attach it and the email goes through.
A simple routine to compress BMP files well
Decide where the picture is going and how large it needs to be. Keep the original BMP safe. Compress BMP files once, from the original, at the smallest setting that still looks right, and check small text at reading size. Then use the PNG: send it, publish it, or turn it into something lighter with PNG to WebP. If you want to mark it, add a watermark, and if the picture started life as a phone photo rather than a scan, convert it from HEIC to JPG instead. This routine takes a minute, and it works whether you compress BMP files once a year or every day.
Why it is worth converting old BMP files soon
Old BMP files tend to pile up unnoticed, and the longer they sit, the more likely it is that nobody remembers what they are. Converting them to compact PNGs while you still know where they came from is far easier than doing it years later. If you compress BMP files in batches as part of a tidy-up, you also get a chance to name them properly, which makes the archive useful rather than merely large. A little time spent now to compress BMP files saves storage, makes backups faster and means the pictures can be opened on any device without special software.
Before you close the page
Check that you downloaded the PNG, that it looks fine at the size you will use, and that you kept the original BMP.
Summary
To compress BMP files here, drop the image, pick a resolution and download the result. The picture is saved as a PNG, which is lossless and far smaller, so every colour is kept exactly, and the dpi from the BMP header is carried over. The result is a PNG, not a BMP, because staying in BMP would mean staying the same size. Nothing leaves your device.