Exposure Discrepancy - DNG Still Images

[brett8883]

Perfect explanation of how it works!

Thanks, I would add that he almost certainly would mind motion blur ?

 

[Dave Maine]

That doesn't match my experiences. I have been shooting raw in my Nikons for many years. Nikon's raw format is a proprietary format NEF, which is not TIFF. It is extraordinarily versatile having at least 1.5 stops more dynamic range than any TIFF created from it. The Adobe DNG converter creates a DNG file with the same amount of flexibility. Both when you compare them with a TIFF with it's broadest luminosity range are much better. Once you transcode to TIFF, that is all lost. That is why raw converters are made, to get a TIFF which has the RAW or DNG reduced to look good in a TIFF with it's limits.

 

[Dave Maine]

We are going no place with this. Try it for yourself with a good raw image from a newer Canon or Nikon and see for yourself.

 

[Citizen Flier]

I'm still having exposure discrepancy issues, which do NOT occur with my Canon DSLR, or high end Panasonic compact. I typically shoot at Golden Hour, and bracket my exposures, erring slightly under to avoid blown out HL's. I process all stills in Adobe Raw Reader via Bridge. The thumbnails of my land cams are always pretty consistent with what I see on the camera screen and the same images in Bridge. But my M2P stills appear multiple stops darker in Bridge/Raw Reader than they do on the Smart Controller.

I honestly feel there's a mismatch from the M2P images that does NOT occur with the land cams. Is there a feature to adjust/calibrate the Smart Controller Screen? They are advertised as having bright screens, & highly visible in direct sun. So perhaps what I'm seeing on the SC is displayed with higher luminance or Gamma than what's actually captured. (And yes, I do understand that the DNG is a Digital Negative, and has a fews stops leeway) But as mentioned, there are far fewer surprises with the land cams.

And when I adjust the images in Raw Reader to better match what I recall at capture, additional noise is generated in shads/mids. My workstation monitor is well calibrated, and typically represents wheat I get from my printer, etc. So I'm thinking the SC needs to either be calibrated, or have the screen luminance adjusted. Thanks.

 

[Not A Speck Of Cereal]

They are advertised as having bright screens, & highly visible in direct sun. So perhaps what I'm seeing on the SC is displayed with higher luminance or Gamma than what's actually captured.

That's probably it. If you can find a brightness setting, that could help, but make the screen less visible outdoors.

But here's another aspect to consider though, which might help:

I typically shoot at Golden Hour, and bracket my exposures, erring slightly under to avoid blown out HL's

I don't understand why you are doing this. Slightly under for a single shot, yes. But with bracketing, your main shot is supposedly the middle/base/"correct" setting (not over or under). The PLUS value shots are *supposed* to have blown highlights, because you're specifically capturing those shots to better expose the shadow detail.

When you blend the images (or feed it to an app that does), the blown areas are tossed out / not used.

So if you are under-exposing the base exposure, then instead of "0, +1. -1", you might be getting "-1, 0, -2" with no positive values at all.

This would be true for DSLR photography as well.

 

[Dave Maine]

A practical way to move this discussion forward, would be to do 2 experiments. Take a still picture with the smart controller and observe the histogram display on the sc. Note particularly the histogram near black, and near white. Then take that image off the SD card and import it into you PC editing program, and observe the histogram. If everything is working correctly, The histograms should match exactly.

Repeat with video and compare the 2 histograms.

DJI processes video from sensor raw into rec 709 color space which defines both gamma and color interpretation, and re-encodes both into a H.264 or H.265 representation. This process seems to map perfectly for me.

The still photograph flow is less clear to me. Earlier debates in this forum don’t sway me. The RAW that I get out of DJI DNG are tiffs, with rgb data encoded already in them. The Nikon raws that I am used to, when converted to dng retain actual raw sensor data without any conversion, and can be left in raw for the full power of the various raw converters. The DJI raw tiffs clearly lack this flexibility, convincing me that DJI has at least partially processes their sensor data into some kind of rgb color space whose standard is unknown to me.

The histogram experiment could shed further light on what is actually going on.

 

[Not A Speck Of Cereal]

That would suck if DJI isn't actually create a valid DNG file (but still calling it DNG). That would explain a lot though.

Good plan with the histogram experiment.

 

[Deleted member 114292]

A practical way to move this discussion forward, would be to do 2 experiments. Take a still picture with the smart controller and observe the histogram display on the sc. Note particularly the histogram near black, and near white. Then take that image off the SD card and import it into you PC editing program, and observe the histogram. If everything is working correctly, The histograms should match exactly.

Repeat with video and compare the 2 histograms.

DJI processes video from sensor raw into rec 709 color space which defines both gamma and color interpretation, and re-encodes both into a H.264 or H.265 representation. This process seems to map perfectly for me.

The still photograph flow is less clear to me. Earlier debates in this forum don’t sway me. The RAW that I get out of DJI DNG are tiffs, with rgb data encoded already in them. The Nikon raws that I am used to, when converted to dng retain actual raw sensor data without any conversion, and can be left in raw for the full power of the various raw converters. The DJI raw tiffs clearly lack this flexibility, convincing me that DJI has at least partially processes their sensor data into some kind of rgb color space whose standard is unknown to me.

The histogram experiment could shed further light on what is actually going on.

Note that a Nikon NEF file also contains a low res JPEG as do all RAW file formats.

All DNGS are TIFF files - but a TIFF file can contain a raw image.

TIFF IS JUST A STRUCTURED FILE FORMAT THAT CAN CONTAIN ANY KIND OF IMAGE.

From the DNG file specification:

TIFF Compatible

DNG is an extension of the TIFF 6.0 format, and is compatible with the TIFF-EP standard. It is possible (but not required) for a DNG file to simultaneously comply with both the Digital Negative specification and the TIFF-EP standard.

'One of the uses of TIFF/EP is as a raw image format."

 

[Deleted member 114292]

I'm still having exposure discrepancy issues, which do NOT occur with my Canon DSLR, or high end Panasonic compact. I typically shoot at Golden Hour, and bracket my exposures, erring slightly under to avoid blown out HL's. I process all stills in Adobe Raw Reader via Bridge. The thumbnails of my land cams are always pretty consistent with what I see on the camera screen and the same images in Bridge. But my M2P stills appear multiple stops darker in Bridge/Raw Reader than they do on the Smart Controller.

I honestly feel there's a mismatch from the M2P images that does NOT occur with the land cams. Is there a feature to adjust/calibrate the Smart Controller Screen? They are advertised as having bright screens, & highly visible in direct sun. So perhaps what I'm seeing on the SC is displayed with higher luminance or Gamma than what's actually captured. (And yes, I do understand that the DNG is a Digital Negative, and has a fews stops leeway) But as mentioned, there are far fewer surprises with the land cams.

And when I adjust the images in Raw Reader to better match what I recall at capture, additional noise is generated in shads/mids. My workstation monitor is well calibrated, and typically represents wheat I get from my printer, etc. So I'm thinking the SC needs to either be calibrated, or have the screen luminance adjusted. Thanks.

The display on the SC is not meant to be a way to judge exposure per se.

That's what the light meter and histogram are for.

I assume you mean Adobe Camera Raw (ACR) - when you open a raw image file ACR applies various default settings are applied IF it knows about your camera.
Does ACR know about the DJI camera?

 

[brett8883]

I'm still having exposure discrepancy issues, which do NOT occur with my Canon DSLR, or high end Panasonic compact. I typically shoot at Golden Hour, and bracket my exposures, erring slightly under to avoid blown out HL's. I process all stills in Adobe Raw Reader via Bridge. The thumbnails of my land cams are always pretty consistent with what I see on the camera screen and the same images in Bridge. But my M2P stills appear multiple stops darker in Bridge/Raw Reader than they do on the Smart Controller.

I honestly feel there's a mismatch from the M2P images that does NOT occur with the land cams. Is there a feature to adjust/calibrate the Smart Controller Screen? They are advertised as having bright screens, & highly visible in direct sun. So perhaps what I'm seeing on the SC is displayed with higher luminance or Gamma than what's actually captured. (And yes, I do understand that the DNG is a Digital Negative, and has a fews stops leeway) But as mentioned, there are far fewer surprises with the land cams.

And when I adjust the images in Raw Reader to better match what I recall at capture, additional noise is generated in shads/mids. My workstation monitor is well calibrated, and typically represents wheat I get from my printer, etc. So I'm thinking the SC needs to either be calibrated, or have the screen luminance adjusted. Thanks.

Can you upload a DNG to a drop box or something so we can see what is happening?

 

[Citizen Flier]

That's probably it. If you can find a brightness setting, that could help, but make the screen less visible outdoors.

But here's another aspect to consider though, which might help:


I don't understand why you are doing this. Slightly under for a single shot, yes. But with bracketing, your main shot is supposedly the middle/base/"correct" setting (not over or under). The PLUS value shots are *supposed* to have blown highlights, because you're specifically capturing those shots to better expose the shadow detail.

When you blend the images (or feed it to an app that does), the blown areas are tossed out / not used.

So if you are under-exposing the base exposure, then instead of "0, +1. -1", you might be getting "-1, 0, -2" with no positive values at all.

This would be true for DSLR photography as well.

Thank

 

[Citizen Flier]

The bracket range in the Go4 App does not bracket widely enough to expose for Sky & trees/Foliage at dusk IMO. So I manually bracket adjusting shutter speed. I typically do a "correct" exposure & a couple of darker frames for the sky/sun. I compose in Camera Raw as HDR.

If ACR DOESN'T recognize a camera, I believe it can't be opened in ACR. As I consider this more. So I believe ACR DOES recognize the M2P.

I believe it could be the screen brightness meant to be visible without a sunshade -which I appreciate. I notice that images captured in bright sun don't have the same degree of discrepancy as low light shots. Makes me think the screen brightness in bumped in darker images. I'll probably have to learn to work around it, and bracket with slightly overexposed images. EZPZ.

I just did a quick web search & came up with this little nugget that I hadn't yet discovered.

DJI Smart Controller Review - Newsshooter

The DJI Smart Controller for the Mavic Pro 2 and Mavic Zoom 2 was just recently announced at CES 2018, and here at Newsshooter, we have been lucky enough

www.newsshooter.com

Here's some revealing text:
"The ultra-bright display has an output of 1000 cd/m2, twice the brightness of most standard smartphones, and has been optimized for use in direct sunlight. The brightness can be manually and automatically adjusted. When Auto mode is enabled, the DJI Smart Controller will automatically adjust its brightness using a built-in light sensor, making it optimal for the human eye according to the surrounding environment. If you go into the settings menu you can actually choose how the screen behaves depending on what conditions you are flying in."

I did a recent exposure test with the MP2 and my DSLR with exactly the same exposure settings & the same target. Very close.

 

[Citizen Flier]

I want to revisit this thread for an unresolved issue. I am fairly well convinced that the very useful bright screen on the Smart Controllers misrepresents what the camera will record in LOW LIGHT. In good light, I find the screen to represent fairly closely how my (RAW) images will appear in post. But in low light, the SC screen image is consistently FAR brighter that what I get from the camera. There is an option to disable the bright screen feature in the controls. I have not yet tested this. Has anyone?
When I shoot with my DSLR the screen image display is fairly consistent with my recorded still images (perhaps a 1/2 stop brighter or less) -in ANY LIGHT. Only in the Smart Controller is there a discrepancy, and that is ONLY in LOW LIGHT. I'm seeking the best way to make low light previews more accurate on the SC. (Flying M2P) Thanks.

 

[Deleted member 114292]

I want to revisit this thread for an unresolved issue. I am fairly well convinced that the very useful bright screen on the Smart Controllers misrepresents what the camera will record in LOW LIGHT. In good light, I find the screen to represent fairly closely how my (RAW) images will appear in post. But in low light, the SC screen image is consistently FAR brighter that what I get from the camera. There is an option to disable the bright screen feature in the controls. I have not yet tested this. Has anyone?
When I shoot with my DSLR the screen image display is fairly consistent with my recorded still images (perhaps a 1/2 stop brighter or less) -in ANY LIGHT. Only in the Smart Controller is there a discrepancy, and that is ONLY in LOW LIGHT. I'm seeking the best way to make low light previews more accurate on the SC. (Flying M2P) Thanks.

How about use the meter. Pro photographers never chimp. The screens not meant to be an exposure Meter.
Or maybe look at the histogram.

 

[Citizen Flier]

How about use the meter. Pro photographers never chimp. The screens not meant to be an exposure Meter.
Or maybe look at the histogram.

Yes, have considered both. Even have a drawer full of light meters. But as stated above, my DSLR previews are reliable enough. Just trying to get same on the SC.

 

[Thomas B]

I mostly fly mr M2P with my CS for just that reason. The CS seems to pretty accurately show what I’m capturing. I shoot most stills in jpeg+RAW (DNG). Pleased with th the results. Use filters when necessary to keep exposure at 4-5.5

 

[Citizen Flier]

I mostly fly mr M2P with my CS for just that reason. The CS seems to pretty accurately show what I’m capturing. I shoot most stills in jpeg+RAW (DNG). Pleased with th the results. Use filters when necessary to keep exposure at 4-5.5

Thanks. Assume by "CS" you meant Smart Controller? Do you shoot in low light - dawn/dusk? That is the ONLY time my SC preview is off. And that's the main point of my post.

 

[Thomas B]

Thanks. Assume by "CS" you meant Smart Controller? Do you shoot in low light - dawn/dusk? That is the ONLY time my SC preview is off. And that's the main point of my post.

No I meant Crystalsky (7.8”), not SC.. I have an SC but rarely use it.

 

[chong67]

A dng file is an extension of the TIFF file format and is a container for the RAW data. Does not mean it is not RAW data

https://www.adobe.com/content/dam/acom/en/products/photoshop/pdfs/dng_spec_1.4.0.0.pdf

So TIFF and DNG are the same?