About

Data URI to Bitmap conversion requires precise binary encoding to generate valid BMP files. Incorrect header construction leads to corrupted images that fail to open in standard viewers. This converter implements the Windows BMP v3 specification with 24-bit RGB color depth and mandatory 4-byte row alignment padding.

The tool processes Data URIs up to 10 MB, extracting the base64 payload and decoding it to raw pixel data via Canvas API. The BMP encoder calculates the exact file size as fileSize = 54 + height × rowSize, where rowSize includes padding bytes. Each pixel undergoes RGBA to BGR conversion with alpha channel removal, maintaining color accuracy while reducing file size by 25%.

Formulas

BMP file structure follows strict binary encoding rules for compatibility across platforms. The core formula for calculating the total file size accounts for header overhead and row padding alignment:

fileSize = 14 + 40 + imageDataSize

where the image data size includes mandatory padding:

rowSize = ⌈width × 34⌉ × 4

imageDataSize = rowSize × height

Legend: width = image width in pixels, height = image height in pixels, rowSize = bytes per row including padding

Reference Data

BMP Header Field	Offset (bytes)	Size (bytes)	Typical Value	Description
Signature	0	2	`0x424D` ('BM')	File type identifier
File Size	2	4	Variable	Total file size in bytes
Reserved 1	6	2	0	Application-specific
Reserved 2	8	2	0	Application-specific
Pixel Offset	10	4	54	Start of pixel data
DIB Header Size	14	4	40	BITMAPINFOHEADER size
Image Width	18	4	Variable	Width in pixels
Image Height	22	4	Variable	Height in pixels
Color Planes	26	2	1	Must be 1
Bits per Pixel	28	2	24	RGB color depth
Compression	30	4	0	BI_RGB (uncompressed)
Image Size	34	4	Variable	Pixel data size with padding
X Resolution	38	4	2835	Pixels/meter horizontal
Y Resolution	42	4	2835	Pixels/meter vertical
Colors Used	46	4	0	0 = all colors
Important Colors	50	4	0	0 = all important

Frequently Asked Questions

BMP files store uncompressed pixel data, making them approximately 3-10 times larger than compressed formats like JPEG or PNG. A 1920×1080 image requires exactly 6,220,854 bytes in BMP format versus ~200 KB as JPEG. The format trades file size for zero compression artifacts and faster read/write operations.

BMP v3 format doesn't support alpha transparency. The converter composites transparent areas against a white background (RGB 255,255,255) before encoding. For images requiring transparency preservation, consider using BMP v4 with ARGB format or alternative formats like PNG.

BMP stores pixels in BGR order (Blue-Green-Red) instead of RGB, and rows are stored bottom-to-top by default. This converter handles both conversions automatically. Corruption typically occurs from incorrect row padding - each row must be padded to a 4-byte boundary regardless of pixel count.

The tool processes images up to 8192×8192 pixels (67 megapixels) to prevent browser memory exhaustion. Larger images would generate BMP files exceeding 200 MB. For gigapixel images, use server-side processing or specialized imaging software.

Yes, the Canvas API automatically rasterizes vector formats (SVG) and decodes modern formats (WebP, AVIF) if the browser supports them. The converter samples at the SVG's viewBox dimensions or uses a default 1024×1024 resolution if dimensions are undefined.