What exactly does DRO do, and how does it work?
My Sony Alpha 77 has a DRO mode, which is on by default and I have been using it most of the time. I understand that it aims to improve dynamic range much like HDR, without actually needing multiple exposures, but what does it do exactly as in how does it work, and am I losing anything if I keep it on and shoot in raw? Also what are the different settings for, Auto and +1 to +5?
Peripheral comment: be VERY careful when using DRO with flash. It has very good and very bad aspects: It can be immensely useful with eg a long table of people where the flash lighting drops as inverse square and exposure levels at the near and far end are vastly different- DRO can do an excellent job of balancing the apparent illumination levels so the scene is (apparently) much more evenly lit. | HOWEVER: When used on groups of people it can vastly wash out details on skin tones in high illumination area. People with darker faces may end up with "coffee coloured slabs" in place of skin ...
... images. I found this out the hard way with my A77. DRO is still useful in such cases but due care is needed.| Higher numbered DRO levels adjust lighting more aggressively in areas of different illumination. DRO 5 will create the most evenly illuiminated images at the cost of loss of reality. || If shooting a scene where you wish to maintain or emphasise high contrast, turn DRO off. True black is often impossible to obtain with DRO on as it sees black as an opportunity to adjust effective dynamic range.
DRO stands for Dynamic Range Optimization. It is designed to fit more dynamic range into images. A single exposure is still taken so you are always limited to the sensor's latitude. However, from what the sensor captures, more or less of that range is mapped into images. With fixed values, the transform is applied the same to each image. With Auto, it depends on feedback from the metering system and the mapping from sensor dynamic-range to images will be adjusted accordingly.
DRO is one of the few settings which indirectly impacts RAW files. While its designed as processing, which normally effects JPEG and TIFF files only, the camera adjusts exposure to have more dynamic range available for the mapping, often reducing exposure to get more details in highlights. If you shoot RAW and Manual mode though, DRO will have no effect.
Does it reduce only exposure (time? aperture?) to retrieve details from the highlights? Or does it shift the whole available dynamic range? Where did you find this information?
Generally, it chooses to reduce exposure slightly. That depends on the exposure latitude of the sensor and data obtained from metering sensor, so on some scenes the shutter-speed could be increased, while on others not. Personally, I almost always shoot in A and with fixed ISO, so maybe it could change those parameters if they were free. There might be differences between cameras but I've tested this on fewer than 10 Sony models. On the A7R IV, the exposure hasn't moved among the few tests shots taken. I conferred with Sony Expert Gary Friedman to validate this.
That's interesting and might be the case for A-priority mode. I doubt it's the case e.g. in manual mode. Where did you get that information? Or is it just something you think happens based on experience?
Manual with fixed ISO, nothing could be changed. I doubt it does but I will try it later or this weekend. Yes, I have seen it happen but because the A7R IV is more complex and allows the tone-curve to be finely controlled, I wondered how this interacted with DRO and so I discussed it with Gary Friedman who is a known expert on Sony cameras (as opposed as my expertise on image processing since 20+ years and general digital camera reviewer for 15 years).
@CountZero - You're welcome! Did a few tests this weekend using the A7R IV and I can confirm this discussion. When an exposure parameter is free, it will change it when the scene has an extreme dynamic-range. In Manual exposure, all parameters are fixed and no DRO level changes it. With A or S mode, then it can change it up to one stop when using higher level correction (DRO Level 3-5) and it seems to do it fair consistently.