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Correcting the green shadows


Guest JonathanP

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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?

 

Since there's no electronic shutter, if they were making two exposures, we'd hear it.

 

Jim

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Since there's no electronic shutter, if they were making two exposures, we'd hear it.

 

Jim

 

I agree that they are not doing two exposures. I'm just intrigued buffer size being cut in half, which makes me wonder what they are doing with the other half of the RAM. Maybe they are just reserving it to buffer a copy of the original capture, that has been noise reduced, before dumping it to the card. Thus half the capacity

Edited by thrid
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Maybe we could flip it around and ask why the buffer is 2x deeper at lower ISOs, which happens to correspond to the green shadow tinge? Maybe ISO 1250 and higher files are not getting extra special treatment and instead it's something with the lower ISO files getting 'chopped'?

 

I just did a test for curiosity's sake comparing buffer capacity and card write times for compressed and uncompressed M240 DNGs (from an empty buffer until the first pause in the continuous advance frame rate). For both, buffer depth is ~12 frames at ISO 1000 and lower and ~6 frames at ISO 1250 and higher.

 

Card write speed is about 2x shorter when set to compressed.

 

Interestingly, M240 buffer performance is identical, whether set to DNG or Jpeg. Of course card write time is much shorter with Jpeg.

 

Whether or not this means anything, what it says to me is that final compressed file size is not relevant to buffer capacity as I'm accustomed to it being with Canon's DSLRs. While Canon's DSLRs only offer one flavour of RAW files, buffer depth increases dramatically when set to Jpeg (but as with the M240, also decreases as ISO increases, though not necessarily as extremely as the M240).

 

Oh, and frame rate at ISO 1250 and higher is more around 2fps... just to me it feels very slow and seems like 1fps. :)

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Jonathan was kind enough to give me access to the plug-in while in beta. I had no problems with it.

 

A question I had earlier was whether it would work as well with higher ISO files as it does at ISO 200. While I've only tried a few so far, ISO 1000 images show noticeable shadow improvement. The green tinge is gone and the red RGB value is very close to the green value. In the original files, the red value is always somewhat lower than green. Deep shadow tonality is also smoother.

 

For fun, I tried a couple ISO 1600 and 3200 files. Interestingly, there is almost no difference between the original files and those processed through the app. The RGB values differ slightly, but visually, there is no discernible difference.

 

Thanks for this, Jonathan!!

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I've now developed a Lightroom plugin (Mac only) that I have made freely available:

 

 

 

I believe this is highly appreciated among the members here.

Would making a win version be too much effort for you?

 

I understand making money out of it isn't your priority, but I'd gladly contribute if needed.

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Hey Jonathan

 

I downloaded the LR plugin and have been playing around with it. It certainly cures the green shadows, but I also noticed that it seems to effect the highlights.

 

If I set the highlight recover to -100 I can now see a pink 'hole' in the highlights, that previously was not there.

 

Are you doing a global offset in the green channel, that is affecting the entire image or are you tapering off the effect as you approach gamma or white point??

 

I'm going to a test under daylight and see if I still get the same results. The attached picture was shot under fluorescents, which have a nasty green spike, so this may be an exaggerated example, but I think it is still worth investigating what is happening here.

 

thanks again for your work,

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Edited by thrid
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Guest JonathanP

Hi Feli,

 

Are you doing a global offset in the green channel, that is affecting the entire image or are you tapering off the effect as you approach gamma or white point??

 

The non-linearity correction is applied to all channels, the offset tapering off to values of 400. In other words, no adjustments are made to any pixel (regardless of channel) where the pixel value is greater than 400.

 

Having said that, there does appear to be a very slight overall lifting of values, which is not directly due to my processing, but perhaps to the DNG to DNG conversion of the Adobe SDK (I let the SDK save the newly created DNG in the latest v1.4 format), which results in all the associated metadata being decoded and then re-encoded. I wasn't sure whether to force the SDK to make the output the same v1.3 as the input file. Haven't quite tracked down what causes the very slight overall increase, but I've not found it a problem when processing any real world images. I'll keep digging and do an update if I can find it.

 

Would you use a highlights recovery of -100 on a real image though, as its effects can be quite undesirable?

 

Thanks for the feedback :)

 

Jonathan

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Guest JonathanP

Would making a win version be too much effort for you?

I understand making money out of it isn't your priority, but I'd gladly contribute if needed.

 

Unfortunately I don't have any Windows machines either at work or home (not strictly true as I have an old XP machine for the scanner), I just use Mac + Linux, and I'm not a Windows programmer. Having said that, the part of the plugin that is Mac specific is my command line processing tool and doesn't need any Windows GUI programming - it may be possible for me to recompile it using one of the open source windows C compilers on my scanner PC. I will investigate to see if that would be possible, but I can't promise anything, sorry.

 

Jonathan

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Hi Feli,

 

 

 

The non-linearity correction is applied to all channels, the offset tapering off to values of 400. In other words, no adjustments are made to any pixel (regardless of channel) where the pixel value is greater than 400.

 

I see. thanks for the explanation. I'm going to do some more test.

 

Would you use a highlights recovery of -100 on a real image though, as its effects can be quite undesirable?

 

Thanks for the feedback :)

 

Jonathan

 

Depends. Sometimes you just need to turn it to 11.

:-)

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I tried your plug-in on a severely under-exposed picture (requires Exposure +4.65) in Lightroom 5.5 on a Windows 7 machine—and it works like a charm.

 

In Camera Raw and Lightroom, there is a Shadow Tint slider in the Camera Calibration pane. You can use that, instead of Jonathan's plug-in, to mitigate the green shadows in pulled-up pictures from the M (Typ 240). However this slider affects the upper shadows (three-quarter tones) too much and the deepest shadows not enough. It's better than nothing but far from perfect.

 

Jonathan's plug-in, in contrast to said Shadow Tint slider, does a near-perfect job.

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Thanks very much for all your work! The plugin works amazingly well. Is there a way I can paypal you a contribution for the use of the plugin?

 

Cheers,

KL

 

After a little wrestling with Windows compilers, I've released a new version of my Lightroom Plugin that now works on both Windows and Mac :)

 

Download it from my downloads page here and further info here.

 

Hope its of use,

Jonathan

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Thank you Jonathan. It's very generous of you to share your time and talents.

 

I just tried your plugin on a night shot with deep shadows. It did an amazing job of removing the green tint.

 

I also tried drastically increasing the saturation and shadow recovery in order to exaggerate the effects. Both of the images below have exactly the same Lightroom settings. The only difference is one image was processed with your plugin. Looks great, although I'm wondering if there is some slight loss of shadow detail (certainly don't want to be critical, just analytical). Need to do more checking.

 

Thanks again!!!!!!

 

No Plugin (drastically increased shadow detail and saturation for illustration purposes only)

 

14842954045_234240f7f2_c.jpgNo Plugin by brusbybrusby, on Flickr

 

 

 

After applying Plugin (same exaggerated Lightroom settings as above)

 

14656408477_433d34d878_c.jpgPlugin by brusbybrusby, on Flickr

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  • 2 weeks later...

A great tool Jonathan. Thanks for all your efforts. Leica should be listening...and looking.

 

Shot at ISO 200 with 5 stops under exposure. Left plain Leica, right with Jonathans correction.

 

Herb

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