XBM to JPG Converter

Encoding: the XBM uses none: bits written as hexadecimal bytes in C source; JPG uses lossy DCT coding in 8×8 pixel blocks, with colour usually stored at half resolution, and the download is a standard JPEG at the quality you choose.

Bit depth: 1 bit per pixel in the XBM; JPG allows 8 bits per channel, and the JPG written here has 8 bits per channel.

Colour: two colours, foreground and background in the XBM; JPG supports YCbCr shown as RGB, greyscale, or CMYK from print software, written here as 8-bit sRGB.

Metadata: the XBM can carry the #define names for width, height and an optional hotspot; JPG can carry EXIF (camera, date, GPS), XMP, IPTC and an ICC profile in APP segments, but nothing is copied across.

XBM is the 1-bit image format of the X Window System, written as C source code so it can be compiled straight into a program. It was used for cursors, icons and window decorations, and early web browsers displayed it.

An XBM file is C code: '#define name_width 16', '#define name_height 16', optional x_hot and y_hot lines, then 'static unsigned char name_bits[] = { 0x00, ... };' with each byte holding eight pixels, least significant bit first.

XBM files usually come from X11 cursors, icons and window manager themes, and C programs that embed small bitmaps.

JPEG is the universal photo format. It compresses by discarding fine detail the eye is least sensitive to, which makes photos small but blurs sharp edges and text if pushed too far.

A JPEG starts with the bytes FF D8 and is a run of marker segments: APP1 carries EXIF and often a thumbnail, APP2 an ICC profile, DQT the quantization tables that decide the quality, and SOS the compressed scan, which ends at FF D9.

JPG is the better choice for photographs that need to open anywhere, while XBM suits X11 cursors, icons and C programs that embed bitmaps.

JPG strengths: Opens everywhere: every browser, phone, camera, printer and app; Small files for photographs; Adjustable quality from tiny to near-lossless. Drawbacks to weigh: No transparency; Lossy: every re-save loses a little more; Blocky artifacts around text, logos and sharp lines.