PAM to JPG Converter

Encoding: the PAM uses none; 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: 8 or 16 bits per channel in the PAM; JPG allows 8 bits per channel, and the JPG written here has 8 bits per channel. 16-bit PAM files are reduced to 8 bits per channel.

Colour: greyscale or RGB, as declared by the TUPLTYPE line in the PAM; JPG supports YCbCr shown as RGB, greyscale, or CMYK from print software, written here as 8-bit sRGB.

Transparency: the PAM stores it as an extra channel declared as GRAYSCALE_ALPHA or RGB_ALPHA; the JPG has none, so transparent areas are filled with the colour you choose.

Metadata: the PAM can carry only comment lines in the header; JPG can carry EXIF (camera, date, GPS), XMP, IPTC and an ICC profile in APP segments, but nothing is copied across.

PAM is the general member of the Netpbm family: an uncompressed format with a self-describing header that can hold greyscale, RGB and alpha channels at 8 or 16 bits.

A PAM file starts with 'P7', then header lines WIDTH, HEIGHT, DEPTH (channels), MAXVAL and TUPLTYPE (for example RGB_ALPHA), closed by ENDHDR, followed by the raw samples row by row.

PAM files usually come from Netpbm and ImageMagick pipelines, research code and tools that need a simple RGBA file.

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 PAM suits image processing pipelines that need alpha.

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.