Correcting the green shadows

[thrid]

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I do think its a bit of a shame that out of the camera the image quality is not limited by the sensor*, but by the image processing pipeline. It must be a little frustrating for CMOSIS to keep hearing everyone laud the Sony sensors when theirs isn't getting the best exposure.

 

Jonathan

*the non-linearity may of course be in the sensor ADC, but I think it's fair to think of performance as a combination of silicon+software

 

Internal processing by the camera or on the post end?

Edited July 18, 2014 by thrid

[JimKasson]

Even if this problem is inherent in the hardware, they should be able to compensate for it with software as Jonathan has demonstrated. Or at least I would think they could.

 

Jonathan's software is an existence proof that much, if not all, of the problem can be fixed in post. Therefore, it could be fixed in Lr. Eric Chan, are you monitoring this forum?

 

Jim

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[thrid]

Jonathan's software is an existence proof that much, if not all, of the problem can be fixed in post. Therefore, it could be fixed in Lr. Eric Chan, are you monitoring this forum?

 

Jim

 

Can you offset channels / black point in LR? It's also something you want to do as part of the debayering process, not after. Correct?

 

LR is not my primary software, so I'm still not familiar with all of its features

Edited July 18, 2014 by thrid

[JimKasson]

Can you offset channels / black point in LR?

 

As far as I know, no. Maybe with a profile... I use Lr every day and there's still a lot about it I don't know.

 

It's also something you want to do as part of the debayering process, not after. Correct?

 

Before the demosaicing, actually.

 

Jim

[fotofool]

Jonathan's software is an existence proof that much, if not all, of the problem can be fixed in post. Therefore, it could be fixed in Lr. Eric Chan, are you monitoring this forum?

 

Jim

 

Alternatively, you and Jonathan could team up to produce a LR plug-in. I'll bet a fair number of people would happily pay a small fee to download it. If it is a problem for many that may push Leica to address it with a firmware update. If it is a problem for only a few at least those few would have a solution. Either way you guys would be compensated for all the time you seem to have spent on this.

[thrid]

I think Adobe Speedgrade will allow you to make adjustments to the DNG image data before or during debayering. But I doubt everyone is going to run out and buy a copy.

 

Maybe also Pomfort ClipHouse...

 

But again, if this is something that needs to be addressed as part of then debayering process then it sounds like this is an issue that can only be resolved by Leica with a firmware update, Adobe CameraRAW or a standalone program like the one developed by Jonathan.

[JimKasson]

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I think Adobe Speedgrade will allow you to make adjustments to the DNG image data before or during debayering. But I doubt everyone is going to run out and buy a copy.

 

I downloaded SpeedGrade CC 2014 and couldn't figure out how to open an M240 DNG file. But maybe it's just trickier than I am. I does look like it's aimed squarely at video.

 

Jim

[thrid]

I downloaded SpeedGrade CC 2014 and couldn't figure out how to open an M240 DNG file. But maybe it's just trickier than I am. I does look like it's aimed squarely at video.

 

Jim

 

There may be a difference between DNG and CinemaDNG...

 

 

But you are correct, it is aimed and film and video production.

 

Longshot!

[thrid]

Keep in mind that I'm not an engineer, but here is a thought...

 

Could this issue somehow be related to white balance? Is the 240 shifting the black and white point to achieve color temperature balance and not smart enough to realize that it's crushing the blacks in certain channels?

 

It would be interesting to check if this still occurs after white balancing off a calibrated target.

[JimKasson]

Keep in mind that I'm not an engineer, but here is a thought...

 

Could this issue somehow be related to white balance? Is the 240 shifting the black and white point to achieve color temperature balance and not smart enough to realize that it's crushing the blacks in certain channels?

 

It would be interesting to check if this still occurs after white balancing off a calibrated target.

 

I've seen no indication the M240 in-camera WB settings affect anything but the EXIF data in raw files.

 

Jim

[jaapv]

Leica did shift the black point when they went from the M8 to the M9.

The reason was noise reduction. It was discussed in this forum at the time.

[JimKasson]

Leica did shift the black point when they went from the M8 to the M9.

The reason was noise reduction. It was discussed in this forum at the time.

 

Have you heard anything from Leica that would indicate that the M240 black clipping and departure from linearity is the results of a deliberate engineering decision?

 

Jim

[jaapv]

At the time of the introduction, as I recall, the clipping was a deliberate decision. It was part of the measures taken to reduce noise. I wouldn't know about the depart from linearity.

[JimKasson]

At the time of the introduction, as I recall, the clipping was a deliberate decision. It was part of the measures taken to reduce noise. I wouldn't know about the depart from linearity.

 

Thanks. In a way, that's good news, because I think it raises the odds that it can be fixed if Leica wants to. Compared to all of the more-sophisticated ways to deal with noise in post-production, clipping is like trying to kill a fly with a hammer.

 

Jim

[rscheffler]

The green shadow problem is something that bothers me, too, and would like to see a solution for it, whether it be from Leica, Adobe or from Jonathan.

 

I also agree with Jeff's suggestion and would be willing to pay a modest fee for such a plug-in or app from Jonathan, if that would help expedite its availability and ease of use.

 

You are right Jonathan.

 

Here's another piece of the puzzle that I discovered yesterday. When I started testing the a7S, I started doing my noise floor measurements in 1/3 stop ISO increments in order to get at when that camera changed conversion gain. I thought I'd take a look at the M240 at 1/3 stop intervals. Here's what I found:

 

http://www.kasson.com/ll/m240 nf vs iso.PNG

 

Notice the kink in the curve? The processing changes between ISO 1000 and ISO 1250. It's even more apparent if you refer the numbers to the input of the pre-ADC amplifier:

 

http://www.kasson.com/ll/m240 nf vs iso corr.PNG

 

Notice that the curve is backwards from most cameras, in which the sensor-referred read noise drops as ISO goes up.

 

I'll be doing a blog post on this with more details some time in the next few days; I'm backed up with the a7S testing.

 

Jim

 

I'm not surprised to see this because it is precisely the threshold at which the M240's continuous advance changes from ~3fps to ~1fps and one reason I almost never shoot above ISO 1000 with it. One reason I upgraded to the M240 from the M9 was for its improved shot to shot responsiveness, which I find invaluable for my style of work, but was disappointed with the fps slowdown at ISO 1250 and higher.

 

Jim, without going back through all of your M240 blog pages, wasn't it your finding that your ISO 1600 and higher test images had a different quality when pushing the shadows? IIRC, ISO 200-800 looked very green, while ISO 1600 and 3200 were OK.

 

Edit: your post comparing results against the RX1 illustrates this nicely: Leica M240 green shadows, part 2 | The Last Word

 

I still think this was a reaction by Leica to harsh criticism of strong banding evident in heavily tweaked images from preproduction cameras (I was guilty of criticizing this)...

Edited July 21, 2014 by rscheffler

[JimKasson]

I'm not surprised to see this because it is precisely the threshold at which the M240's continuous advance changes from ~3fps to ~1fps and one reason I almost never shoot above ISO 1000 with it. One reason I upgraded to the M240 from the M9 was for its improved shot to shot responsiveness, which I find invaluable for my style of work, but was disappointed with the fps slowdown at ISO 1250 and higher.

 

I never made the connection. Good pickup.

 

Jim, without going back through all of your M240 blog pages, wasn't it your finding that your ISO 1600 and higher test images had a different quality when pushing the shadows? IIRC, ISO 200-800 looked very green, while ISO 1600 and 3200 were OK.

 

Yes, indeed. From now on, I'm testing read noise at 1/3 stop intervals.

 

Jim

[rscheffler]

Thanks Jim.

 

FWIW, not only does the fps rate drop at ISO 1250 and higher, but the DNG (compressed) buffer also drops to ~6-7 frames vs. ~12-13...

[Guest JonathanP]

Sorry I've been away on holiday for the last few days and just catching up.

 

Jim, without going back through all of your M240 blog pages, wasn't it your finding that your ISO 1600 and higher test images had a different quality when pushing the shadows? IIRC, ISO 200-800 looked very green, while ISO 1600 and 3200 were OK.

 

Really interesting information from Jim and Ron - I hadn't realised the significance of Jim's results. Does this indicate that above the gain change threshold, the gain non-linearity is much reduced?

 

I wonder why its different? I do hope that the black level clipping and the gain roll off isn't some misguided attempt to reduce low ISO noise in camera. If so, its doing more damage than improvement. Much better to deal with noise in post processing than these side effects.

 

Jonathan

[thrid]

I wonder why its different? I do hope that the black level clipping and the gain roll off isn't some misguided attempt to reduce low ISO noise in camera. If so, its doing more damage than improvement. Much better to deal with noise in post processing than these side effects.

 

Jonathan

 

Since the number of frames you can hold in the buffer is essentially cut in half, could it be that they are doing some sort of noise reduction that involves subtracting one frame from another, which is why they would need the twice the RAM per frame? Or something along those lines?

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[jaapv]

Sorry I've been away on holiday for the last few days and just catching up.

 

 

 

Really interesting information from Jim and Ron - I hadn't realised the significance of Jim's results. Does this indicate that above the gain change threshold, the gain non-linearity is much reduced?

 

I wonder why its different? I do hope that the black level clipping and the gain roll off isn't some misguided attempt to reduce low ISO noise in camera. If so, its doing more damage than improvement. Much better to deal with noise in post processing than these side effects.

 

Jonathan

No, Leica was addressing high-ISO noise.