> > ...so my interest in RAW is mainly to understand current JPEG > behavior/difference with RAW and being able to compare things to "original" > image to make sure everything goes as it should. >
Alexander, Yes, it is exactly the purpose of the "raw" images in the camera > > 2. However, resulting RAW and JPEG images have considerably different > brightness/contrast, suggesting that some parts of processing are done > differently to RAW than JPEG? > > http://www.ndl.kiev.ua/downloads/elphel/image.jpg > http://www.ndl.kiev.ua/downloads/elphel/image_8.raw > http://www.ndl.kiev.ua/downloads/elphel/image_16.raw > > Gamma is set to 1.0 and black level to zero in parameters, that's why > image_8.raw completely matches image_16.raw after normalization. However, > JPEG image image.jpg clearly differs from both of RAW images. I've tried to > perform the same experiment with "factory default" settings (only set WB > off, auto exposure off, color to 0), but result is similar. > > I used your files, converted raw to png with convert -size 2596x1940 -depth 8 gray:image_8.raw image_8.png convert -size 2596x1940 -depth 16 gray:image_16.raw image_16.png Then opened them all using "open as layers" in gimp. Then shifted JPEG image by 2 pixels horizontally and 2 - vertical as raw has 2-pixel border and so total image dimension differs by 4 pixels each direction (these extra pixels are used in color conversion). and - subtracted (shifted) image.jpg from image_8.raw - it matched pretty good - the result seemed black (I admit - I did not add fat zero, so half pixels should be zeros instead of negative). So I incresed contrast with "levels" 32 times, and the result is here: http://community.elphel.com/files/raw/image_diff_contrast.jpeg It is obvious that those were different exposures - you can see there is amplified noise - lower in dark areas, higher - in bright ones (Shot noise) - that is another illustration why it is appropriate to use non-linear compression of the dynamic range. You also can see some dim light near the bottom - I think it is because of 100Hz (or 120Hz if it was in US) modulation of the light source intensity. Anyway - I do not see any difference between raw and JPEG in this eaxample, the difference between shots is definitely larger. You may want to use test modes - it is possible to generate uniform gradient instead of the sensor data (before any conversions) by the FPGA (sensor-independent) or use some test patterns that sesnor can generate itself - both modes are supported through parameters (i.e. with parsedit.php). Andrey
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