How to Convert BMP to PNG

A BMP stores an image as raw, uncompressed pixel data. Every single pixel is written out in full, which makes the format simple and universally readable but also enormous. A PNG holds the exact same picture but wraps it in lossless compression, so it can be a fraction of the size while looking pixel for pixel identical. Converting BMP to PNG is one of the cleanest wins in image handling: you shed most of the file weight and give up nothing in quality.

This is not a lossy trade like re-encoding a JPG. Lossless means the PNG can be decoded back to precisely the pixels the BMP contained.^[3] The only thing that disappears is wasted space. This guide explains exactly how each format stores an image, what the converter does under the hood, which settings matter, and when a different target would serve you better.

What this conversion really does

When you convert BMP to PNG, the picture on screen does not change at all. What changes is how the file is written to disk. BMP records the color of every pixel one after another with no attempt to be economical. PNG takes those identical pixels and applies a lossless compression pipeline that describes the image far more compactly, then reverses that pipeline perfectly on decode. Because the process is fully reversible, the pixels you get back are bit-for-bit the same ones the BMP held. You are not trading quality for size; you are only removing the redundancy BMP never bothered to remove in the first place.

Along the way the conversion can gain you a genuine feature. BMP has no clean, widely supported way to store per-pixel transparency, whereas PNG carries a full alpha channel as part of its core design.^[4] A PNG can therefore hold soft edges and see-through regions that a plain BMP simply cannot express, which matters for logos, icons, and anything layered over other content.

How BMP stores an image

The BMP format, sometimes called a device-independent bitmap, was defined by Microsoft and IBM for the OS/2 and Windows platforms and remains one of the simplest raster formats in wide use.^[1] A BMP file begins with a small file header and an information header that record the width, height, color depth, and layout, followed by the pixel array itself. In the common 24-bit form, each pixel is three bytes, one each for blue, green, and red, and the rows are stored bottom to top with each row padded out to a multiple of four bytes.^[2]

The consequence of that design is blunt: file size grows directly with the pixel count, with essentially no compression applied. A twelve-megapixel image at 24 bits per pixel occupies roughly thirty-six megabytes as a BMP no matter what the picture contains, because a flat white wall and a detailed forest scene both spend the same three bytes on every pixel. That simplicity made BMP fast and predictable for early graphics hardware to read, but it is wasteful for anything you email, upload, or keep in quantity today.

How PNG compresses the same pixels

PNG, the Portable Network Graphics format, was created in the mid-1990s as a patent-free, better-compressing replacement for GIF, and it is now maintained as an international standard and a W3C Recommendation.^[3] Where BMP simply lists pixels, PNG runs them through two cooperating stages. First it applies a filter to each row, which does not remove data but rewrites each pixel as a small difference from a neighboring pixel to the left or above. Flat and gradient regions turn into long runs of zeros or tiny values, which are far more compressible than the raw colors were.^[4]

Second, PNG compresses the filtered data with DEFLATE, the same lossless algorithm used inside ZIP, which combines dictionary matching with entropy coding to pack repeated patterns tightly. Because both steps are perfectly reversible, the decoder reconstructs the exact original pixels. PNG also supports color depths from 1-bit up through full 16-bit-per-channel color, optional palettes for images with few colors, and the alpha channel that gives it clean transparency.

Inside the conversion, step by step

A BMP-to-PNG converter follows a short, deterministic pipeline. It first parses the BMP headers to learn the dimensions and color depth, then reads the pixel array into memory as a plain grid of colors, correcting for BMP's bottom-to-top row order and its row padding. At this point the image exists purely as pixels, with no format-specific quirks left.

Next the converter chooses a PNG color type: grayscale, palette, truecolor, or truecolor with alpha, picking the most economical one that can represent the image losslessly. It then applies PNG row filters, often testing several filter choices per row to find the one that produces the most compressible output, and finally runs DEFLATE over the filtered stream and writes the PNG chunks. Every stage is lossless, so no matter how aggressively the encoder works to shrink the file, the decoded result is identical to the source BMP.

Convert BMP to PNG, step by step

1. Open the tool and add your BMP

   Open the FileFormer image tool and drop the BMP in. Everything runs on your device, so the file is never uploaded.

2. Convert to PNG

   The tool applies lossless PNG compression to the identical pixels. There is no quality setting to worry about, because nothing is being thrown away.

3. Confirm the result

   Preview to see the image looks exactly like the original. It should, since PNG is lossless; the only visible change is the file size.

4. Download the PNG

   Save the smaller file. You can safely delete the bulky BMP once you have the PNG, since no detail was lost.

Settings that affect the PNG

Because PNG is lossless, there is no quality slider that trades detail for size the way JPG has. The controls a good encoder exposes instead change only how hard it works to compress, never what the image looks like.

How much smaller the PNG will be

The saving depends entirely on the content, because PNG can only exploit redundancy that is actually present. An image with large flat regions, solid backgrounds, or repeated patterns, such as a screenshot, a chart, a diagram, or a logo, can shrink to a small fraction of the BMP, sometimes by ten times or more. A busy photographic image with fine grain and continuous tone has far less repetition for the filters and DEFLATE to seize on, so it compresses more modestly, perhaps to half or two-thirds of the BMP.

The one guarantee is direction: a correctly encoded PNG of the same image is smaller than the uncompressed BMP in every realistic case, and never larger, because in the worst case DEFLATE simply stores the data without expanding it. There is no scenario where converting a BMP to PNG costs you image quality, so the only question is how much space you save, not whether you save any.

When PNG is the right target

PNG is the natural home for a BMP because both are lossless and both handle sharp, flat graphics well. If your BMP is a screenshot, diagram, logo, or any image with crisp edges and solid colors, PNG is the ideal destination and this conversion is close to perfect.

PNG versus JPG, WebP, and TIFF

PNG is the safest default for a BMP, but it is not always the smallest. Knowing the honest trade-offs tells you when to reach for something else.

JPG uses lossy compression tuned for photographs, so a photographic BMP saved as JPG is usually far smaller than the same image as PNG. The cost is permanent detail loss and no transparency, which makes JPG a poor fit for text, screenshots, and line art where PNG stays crisp. WebP is the modern middle ground: it offers both a lossless mode that typically beats PNG on size and a lossy mode that competes with JPG, all in one format with transparency support, though a few older tools still cannot open it. TIFF is the archival heavyweight, a flexible container that can hold uncompressed or losslessly compressed images at high bit depths; it is excellent for print and preservation but far less convenient to share on the web than PNG.

The practical summary is that PNG wins whenever you want a lossless, universally supported file with transparency, which covers the vast majority of BMP conversions. Choose JPG or lossy WebP only when the source is a photograph and a smaller file matters more than perfect fidelity.

Common mistakes to avoid

A few recurring points trip people up, and each has a clear answer once you know how the two formats behave.

A frequent worry is that PNG might reduce quality the way saving a JPG does. It does not: PNG is lossless, so the decoded image is bit-for-bit identical to the BMP, and no quality setting exists to degrade it. Another surprise is a PNG that barely shrank, which usually means the source is a noisy photograph with little repetition for the encoder to exploit; that is expected behavior, not a failed conversion, and it is the signal that a lossy format like JPG or WebP would save more if some detail loss is acceptable.

People also sometimes expect the conversion to improve a low-resolution or already-damaged image. It cannot add detail that was never captured; it only re-stores the existing pixels more efficiently. Finally, if a BMP contains transparency information, make sure the converter preserves the alpha channel rather than flattening it against a background, since keeping transparency is one of the main reasons to prefer PNG over the original BMP in the first place.