JPEGencoded

JPEGencoded refers to data that has been compressed using the JPEG image compression standard. The resulting bitstream is used to store or transmit photographic images with reduced file size at the cost of some image detail.

Encoding workflow typically begins with converting the input image from its native color space to YCbCr and applying chroma subsampling, often 4:2:0. The image is divided into 8x8 pixel blocks; each block undergoes a discrete cosine transform, followed by quantization using a quantization matrix. The resulting coefficients are rearranged in a zigzag order and encoded with entropy coding, usually Huffman coding, to produce the final bitstream. The JPEG file format includes markers such as Start of Image, Frame, Define Quantization Tables, Define Huffman Tables, Start of Scan, and End of Image. Variants exist, including progressive JPEG, which encodes the image in multiple scans, and lossless JPEG in a separate family.

JPEGencoded typically implies 8-bit per component color images, most commonly in the YCbCr color space, though the bitstream can carry different configurations. Filenames commonly end with .jpg or .jpeg, and the format can embed metadata such as Exif, IPTC, and XMP. Encoders expose quality settings that adjust the quantization step to balance fidelity and compression.

Advantages include broad compatibility, fast decoding, and effective compression for natural imagery. Limitations include potential loss of fine detail at high compression, possible blockiness and color artifacts, and the lack of native alpha channel support. JPEG is not ideal for text or graphics with sharp edges; for such content, alternative formats or lossless variants may be preferred.