XPM to JPG Converter

Encoding: the XPM uses none: each pixel is one or more characters in C strings; 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: a palette; characters per pixel set how many colours fit in the XPM; JPG allows 8 bits per channel, and the JPG written here has 8 bits per channel.

Colour: a palette of named or hex colours in the XPM; JPG supports YCbCr shown as RGB, greyscale, or CMYK from print software, written here as 8-bit sRGB.

Transparency: the XPM stores it as a palette entry named 'None', which is fully transparent; the JPG has none, so transparent areas are filled with the colour you choose.

Metadata: the XPM can carry comments and an optional hotspot in the values line; JPG can carry EXIF (camera, date, GPS), XMP, IPTC and an ICC profile in APP segments, but nothing is copied across.

XPM is the colour icon format of the X Window System, written as C source with a table that maps characters to colours. It remains in use for Linux application icons and in some toolkits.

An XPM file is a C array of strings: a values line (width, height, number of colours, characters per pixel), one line per colour mapping characters to a colour such as 'c #FF0000' or 'c None', then one string per row of pixels.

XPM files usually come from Linux and X11 application icons, window manager themes and older GTK and Motif programs.

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 XPM suits X11 and Linux application icons.

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.