The reasons are:
a) While producing the JPEG, the camera might create shadow / highlight clipping that was not there in the RAW, due to the lower bits per channel or higher contrast in the JPEG.
b) I've seen some shadow detail recovery from a 14 bit RAW that even the 12 bit RAW from the same camera didn't allow (it was a comparison of 14 vs. 12 bit on that camera). JPEG is only 8 bit (all per channel).
c) Small sensors and high ISOs produce noise. Cameras try to produce reasonable sized JPEGs with small, energy-saving processors. They eat noise and spit it out again, leaving something way harder to deal with when applying noise reduction.
d) JPEGs have white balance applied. If you correct that afterwards, you lose even more of the accuracy of the colors (remember, they already were reduced to 8 bits per channel!).
e) Read reviews. Almost every time, they write about getting more detail, more dynamic range, less noise or less NR artefacts when using RAW.
It's like making a fresh pizza vs. having a frozen one from the supermarket.
More work, but it tastes better.
Marcel
|