sceJpegDecParseHeader and sceJpegDecDecode threw for every down scale
other than 1. SharpProspero's JpegDec.cs documents the factors 1, 2, 4
and 8 and output dimensions that account for the down scale.
Decoder::Jpeg gains DecodeScaled, which decodes through libjpeg-turbo's
scaled inverse DCT, and ScaledDimension, its rounded-up output size.
sceJpegDecParseHeader reports the scaled output size; sceJpegDecDecode
checks the pitch and image buffer against it, writes the scaled image
and packs the output size into its result. A down scale of 1 still
decodes as before. Decode modes other than 0, other down scales and a
down-scaled CMYK or YCCK image still throw.
Federico Marras