WEBP to BMP Converter

Why Convert WebP to BMP

WebP is a modern image format from Google that has conquered the web thanks to superior compression. But what do you do when you need to open a WebP file in software that has no idea this format exists? A CNC machine from 2005, accounting software from the Windows XP era, medical equipment with decade-old firmware - all these systems work perfectly fine but have never heard of WebP.

Converting WebP to BMP is a bridge between the modern web and classic software. BMP (Bitmap) is Windows' native format, introduced in 1986 and supported by absolutely everything that can display images. It's not the most efficient format in terms of file size, but it's the most compatible format in existence.

When you receive an image from a website in WebP format, but need to open it in software that has been running for twenty years without updates - converting to BMP solves the problem radically and unconditionally. BMP will open everywhere because it's the simplest format that any computer with a graphical interface understands.

Why WebP and BMP Are Complete Opposites

The WebP Philosophy: Maximum Efficiency

WebP was created at Google with one goal - to make the web faster. Engineers took developments from the VP8 video codec and adapted them for static images. The result exceeded expectations: WebP files turned out to be 25-35% smaller than JPG at comparable quality, and 26% more compact than PNG for lossless compression.

WebP uses advanced algorithms: predictive coding analyzes neighboring pixels and stores only the differences, discrete cosine transform (DCT) converts spatial data into the frequency domain, and entropy coding eliminates statistical redundancy. All this makes files compact but requires a sophisticated decoder.

Alpha channel support in lossy mode is a unique WebP feature. Neither JPG nor classic GIF can combine transparency with lossy compression. WebP does this elegantly, which made the format popular for web graphics with transparent backgrounds.

The BMP Philosophy: Maximum Simplicity

BMP appeared in a completely different era with completely different priorities. Microsoft was creating Windows 1.0 and needed a format for storing raster images. The requirements were simple: the file should be read quickly, the format should be understandable to any programmer, compatibility matters more than size.

The BMP structure is brilliantly simple. The header reports the image dimensions and color depth. Then come the pixels themselves - row by row, without any compression. Each pixel is described by three bytes: blue, green, red (in that exact order, BGR - a legacy of Intel architecture).

Decoding BMP is trivial: read the header, allocate memory, copy pixels. No complex algorithms, no mathematical transformations. That's why BMP works on any hardware - from supercomputers to microcontrollers with kilobytes of memory.

Technical Aspects of Conversion

Decoding WebP

The first stage of conversion is unpacking WebP. For lossy mode, inverse discrete cosine transform is performed, reconstructing pixel values from frequency coefficients. Dequantization restores the precision lost during compression. Final prediction restores absolute color values from relative ones.

Lossless mode uses a different algorithm: inverse entropy coding, palette restoration, inverse predictive filters. The result is an exact copy of the original image, pixel for pixel.

After decoding, you get an array of pixels in RGBA format (red, green, blue, alpha). For WebP with transparency, the alpha channel contains 256 levels - from fully transparent to fully opaque.

Handling Transparency

BMP technically supports an alpha channel in 32-bit mode, but this support is extremely unreliable. Most programs that work with BMP ignore the alpha channel or interpret it incorrectly. Windows Explorer shows a black background instead of transparency. Paint has no idea what to do with an alpha channel.

When converting WebP with transparency to BMP, the right solution is to replace transparency with a solid color. We use a white background as the most universal option. Semi-transparent pixels are blended with white proportionally to their transparency:

Result = Color x Alpha + White x (1 - Alpha)

A pixel with 50% transparency and red color becomes pink (#FF8080). This is physically correct blending, simulating the overlay of a semi-transparent layer on white paper.

Creating the BMP File

Creating a BMP starts with headers. BITMAPFILEHEADER (14 bytes) contains the "BM" signature, total file size, and offset to data. BITMAPINFOHEADER (40 bytes) describes image dimensions, color depth, and compression type.

Data is written row by row, from bottom to top - this is a historical quirk of the format. Each row is aligned to a 4-byte boundary by adding null bytes. For a 100x100 pixel image with 24-bit color:

• Row data: 100 x 3 = 300 bytes
• Alignment: 300 -> 304 bytes (4 bytes added for 4-byte alignment)
• Total data: 304 x 100 = 30,400 bytes
• Plus headers: 54 bytes
• Grand total: 30,454 bytes

Comparison of WebP and BMP Formats

When converting WebP to BMP, file size increases dramatically. WebP with efficient compression becomes an uncompressed array of pixels. A 1920x1080 image in WebP takes 50-200 KB; in BMP - exactly 6.2 MB (1920 x 1080 x 3 + alignment + headers).

File Size Changes During Conversion

Why BMP Is So Large

BMP uses no compression in standard mode. Each pixel takes exactly 3 bytes (for 24-bit color) or 4 bytes (for 32-bit). File size directly depends on resolution:

The higher the resolution and the more efficient the WebP compression was, the greater the size increase factor.

Formula for Calculating BMP Size

For 24-bit BMP without compression:

Size = ((Width x 3 + Padding) x Height) + 54

where Padding = (4 - (Width x 3) mod 4) mod 4

This is a deterministic formula - BMP size depends only on resolution, not on image content. A photograph and a solid color fill of the same size create BMP files of identical size.

Where WebP to BMP Conversion Is Used

Industrial Equipment

CNC (Computer Numerical Control) machines are one of the main areas of BMP application. Engraving machines, laser cutters, milling machines often work with raster images to create reliefs or engravings.

The firmware of such equipment is developed once and runs for decades. Updates are rare or impossible. WebP for such systems is an unknown set of bytes. BMP is understood unconditionally.

Wide-format printing plotters, especially older models, also prefer BMP. The simplicity of the format means predictable operation without surprises.

Legacy Software

The corporate world is conservative. Software that has been working since 2005 continues to work if you don't touch it. Updating is a risk, an expense, staff retraining. Many organizations operate software created long before WebP appeared.

Accounting systems, warehouse programs, medical information systems - all of this may require images for reports, documentation, identification. And all of this may not understand WebP.

Older versions of Microsoft Office (before 2019) don't support WebP. Inserting an image into a Word document on a computer with Office 2010 requires conversion to BMP, JPG, or PNG.

Embedded Systems

Microcontrollers and embedded systems often have extremely limited resources. A WebP decoder requires significant computing power and memory. A BMP decoder is just a few lines of code.

Industrial displays, information boards, building management systems - all of this can display BMP without any complications. The simplicity of the format is its main advantage in a world of limited resources.

Specialized Software

PCB design software, CAD systems for material cutting, embroidery machine control software - highly specialized software often supports a limited set of formats.

Developers of such programs focus on core functionality, not on supporting exotic graphics formats. BMP is supported by everyone because adding its support is trivial.

What Happens to Quality During Conversion

Lossless WebP -> BMP

If the source WebP was created in lossless mode, conversion to BMP preserves absolutely all pixels. This is a mathematically exact transformation - every color is transmitted without changes.

The only exception is transparency. If WebP contains an alpha channel, semi-transparent areas are blended with a white background. This change is irreversible but visually correct.

Lossy WebP -> BMP

WebP in lossy mode already contains compression artifacts - barely noticeable distortions around high-contrast edges, slight blurring of details. These artifacts were created during initial compression and will remain in BMP.

Conversion to BMP doesn't add new quality losses. BMP stores exactly the pixels that were in the decompressed WebP. Compression artifacts are preserved, but new ones don't appear.

Metadata

WebP can contain EXIF and XMP metadata - information about the camera, shooting date, GPS coordinates, copyright. BMP has extremely limited metadata support.

When converting WebP to BMP, metadata is lost. If EXIF information is important, save it separately or choose a different target format (TIFF or PNG).

Alternatives to BMP Conversion

PNG - The Universal Alternative

For most tasks, PNG is the better choice:

• Lossless compression: file size 3-10 times smaller than BMP
• Alpha channel: full transparency support
• Wide compatibility: all modern systems
• Web compatibility: works in browsers

Choose BMP over PNG only when the target system doesn't support PNG (which is rare) or specifically requires BMP.

TIFF - For Professional Tasks

TIFF provides:

• LZW compression: smaller size without losses
• Metadata: full EXIF, IPTC, XMP support
• Professional standard: printing, archiving

For long-term storage or professional work, TIFF is preferable to BMP.

Keeping WebP

If the target system supports WebP - keep WebP. The format is becoming increasingly widespread:

• All modern browsers
• macOS and iOS from recent versions
• Android natively
• Adobe Creative Cloud
• GIMP, Affinity Photo

Convert to BMP only when WebP is truly not supported.

Practical Recommendations

When to Convert to BMP

Recommended:

• Target software explicitly requires BMP
• Working with industrial equipment
• Embedded systems with limited resources
• Software that hasn't been updated since the 2010s
• Guaranteed compatibility is more critical than file size

Not recommended:

• Photo archive storage (use JPG or PNG)
• Publishing on the internet (keep WebP)
• Email transmission (BMP is too large)
• Long-term archiving (choose TIFF)

Preparing for Conversion

Check WebP contents:

• Is there transparency? It will become a white background
• Is it an animation? Only the first frame will be saved in BMP
• Is metadata critical? It will be lost

Estimate result size:

• Find out WebP resolution
• Calculate BMP size: width x height x 3 bytes = approximate size
• Make sure there's storage space

After Conversion

Verify the result:

• Open BMP in the target program
• Ensure colors are correct
• Check that transparency was handled properly

Keep the original:

• WebP is more compact and higher quality
• Reverse conversion BMP to WebP will increase size without improving quality
• Store source files for possible re-conversion

Technical Limitations of BMP Format

Maximum Dimensions

BMP theoretically supports images up to 2^31 pixels on each side. In practice, most programs are limited to significantly smaller values - usually up to 30,000x30,000 pixels.

For very large images, BMP is impractical: a 30,000x30,000 pixel file in 24-bit color would take about 2.7 GB.

Color Spaces

BMP works in the RGB color space (version 4 and above support ICC profiles). WebP also uses RGB, so conversion doesn't require color space transformation.

However, if WebP was created from a CMYK source (for example, for printing), the CMYK information was already lost when creating WebP. BMP will receive the RGB version.

Byte Order

BMP uses BGR byte order (blue-green-red) - a legacy of Intel x86 architecture. WebP uses standard RGB. During conversion, the byte order is automatically transformed.

BMP Compatibility History

BMP is one of the few formats that works literally everywhere:

Any operating system with a graphical interface supports BMP. It's a fundamental format built into the basic graphics libraries of all platforms.

Conclusion

Converting WebP to BMP is a transition from a modern efficient format to a classic simple one. You sacrifice compactness for absolute compatibility. BMP will open everywhere: in software from 1995, on a CNC machine, in an embedded system with kilobytes of memory.

Use this conversion consciously. If there's an opportunity to work with WebP or PNG - work with them. If the target system specifically requires BMP - convert without hesitation. BMP does one thing, but does it flawlessly: it guarantees the image will open.