Thanks for that concised rendering of what happens during conversion from senor to file format. I think most of us have a fuzzy to semi-sharp idea of what's going on. In my case I read it and quickly forget the finer details.
Tom C. >From: Godfrey DiGiorgi <[EMAIL PROTECTED]> > >What the camera captures on the sensor is RAW data, a 12bit deep >intensity map in an RGB mosaic with one value for each photosite. > >When you instruct the camera to save that data as RAW format, it >writes it to a file on the camera's storage card, structured with the >settings you had made to the camera's rendering engine (sharpness, >contrast, saturation, colorspace, etc) as metadata. The camera >performs none to little processing on RAW data itself, other than >(for some cameras) doing lossless compression. It also renders a >thumbnail and a preview image in highly compressed forms and includes >that in the structured file. > >When you tell the camera to save the data in TIFF format, the camera >takes the RAW data and applies those settings, performs gamma >conversion and chroma interpolation, and then interpolates the >resulting RGB intensity map down to 8bits per channel. This is RAW >conversion rendering to an 8bit RGB representation. It writes the >resulting data out to a file in structured TIFF format. RAW >conversion itself loses significant amounts of data through the gamma >correction function, then the interpolation to [EMAIL PROTECTED] loses >even more data. The result cuts the dynamic range by anywhere from >3-4 stops. > >When you tell the camera to save the data in JPEG format, it does >everything it does for TIFF format and then applies a JPEG >compression algorithm afterwards. Depending upon the subject matter, >the implementation of the JPEG algorithm, the chosen quality level, >and the data itself, this compression can lose very little to quite a >bit over the TIFF. In general, comparing TIFF to JPEG highest quality >format files, the difference is small and not significant to image >quality. Comparing TIFF to highest compression JPEG format, the >difference is substantial. > >A conservative estimate is that the conversion from RAW to TIFF or >JPEG high quality in-camera represents between 40-50% data loss over >the original RAW sensor capture. > >Godfrey > -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
