chris_tribble Posted October 6, 2009 Share #1 Posted October 6, 2009 Advertisement (gone after registration) Hmmm - following up on the compressed DNG discussion I was playing with low, artificially lit colour. Two examples below. 21mm Elmarit pre-asph - which does VERY well on the M9... Both at 1600. Image 1 with Auto WB, Image 2 with Manual WB off a white sheet of paper. The problem is that in the "correct" WB image, if you go in at 100 percent there's a disturbing yellow blotching in the lighter areas (Image 3). Any suggestions? Also - look at how the noise is handled... I also recognise that this is a torture test + that low energy lightbulbs can really b e a pig to work with ... but interesting... Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/99306-m9-low-light-artificial-light-white-balance/?do=findComment&comment=1064675'>More sharing options...
Advertisement Posted October 6, 2009 Posted October 6, 2009 Hi chris_tribble, Take a look here M9 - Low light, artificial light white balance. I'm sure you'll find what you were looking for!
Julian Thompson Posted October 6, 2009 Share #2 Posted October 6, 2009 It is interesting Chris. What happens if you expose it slightly more? Link to post Share on other sites More sharing options...
Jamie Roberts Posted October 6, 2009 Share #3 Posted October 6, 2009 So that looks like chroma noise in the blue channel due to underexposure to me. What RAW converter again? Link to post Share on other sites More sharing options...
gravastar Posted October 6, 2009 Share #4 Posted October 6, 2009 Chris, I've noticed the yellow blotches as well. I have an idea what they may be due to but it's by no means proven. At high ISO under artificial light the blue channel seems to have an offset or blotchy base noise which is absent from the green and red channels. This give an overall blue cast to the image. If the color balance of the image is adjusted to remove the blue it results in the yellow blotches appearing. ie they appear where there was no blue blotch in the uncorrected original. ETA: I haven't tried "clipping" the blue channel black level and then adjusting color balance to see if the yellow blotches are still present. If you look at the separate histograms for the R, G and B channels you can see a very substantial noise peak at low values in the Blue channel. Bob. Link to post Share on other sites More sharing options...
eronald Posted October 6, 2009 Share #5 Posted October 6, 2009 Chris, I've noticed the yellow blotches as well. I have an idea what they may be due to but it's by no means proven. At high ISO under artificial light the blue channel seems to have an offset or blotchy base noise which is absent from the green and red channels. This give an overall blue cast to the image. If the color balance of the image is adjusted to remove the blue it results in the yellow blotches appearing. ie they appear where there was no blue blotch in the uncorrected original. Bob. In tungsten the blue channel is much lower than all the others. One should filter it. Or, better, use an on-lens blue filter to equalize channels during exposure. Edmund Link to post Share on other sites More sharing options...
gravastar Posted October 6, 2009 Share #6 Posted October 6, 2009 In tungsten the blue channel is much lower than all the others. One should filter it. Or, better, use an on-lens blue filter to equalize channels during exposure. Edmund I have a set of blue filters for exactly that, but found in practice they reduced the amount of light so much I gave up using them. The intention was to use them at conventions etc. where the room lighting was dimmable tungsten - the worst possible kind - the color temperature was never consistent or reset to it's original value. Bob. Link to post Share on other sites More sharing options...
chris_tribble Posted October 7, 2009 Author Share #7 Posted October 7, 2009 Advertisement (gone after registration) Thanks for comments - again, I do recognise this is an extreme case (and must be linked with the low-energy light bulbs that we use throughout the flat). So that looks like chroma noise in the blue channel due to underexposure to me. What RAW converter again? I think Jamie's comment is most likely the one that's on the button... re RAW converter I'm using Lightroom with the calibration profile that came up in Thorsten Overgaard's discussions on the forum. I know that I'll be flamed by C1 believers - and it's perfectly possible that C1 does a better job - it's just that I'm now committed to LR for the workflow and will have to live with the CR RAW conversion for the foreseeable future... What I will do when the light drops back later today is to try again is to test the same lighting with exposure bracketing, using manual WB and auto WB... One main comment is that the noise levels at 1600 with the AWB shot are completely acceptable for my work - and are little different from the 5D mkII - but with a more acceptable structure IMHO. Link to post Share on other sites More sharing options...
eronald Posted October 7, 2009 Share #8 Posted October 7, 2009 I have a set of blue filters for exactly that, but found in practice they reduced the amount of light so much I gave up using them. The intention was to use them at conventions etc. where the room lighting was dimmable tungsten - the worst possible kind - the color temperature was never consistent or reset to it's original value. Bob. Yeah, low tungsten is a pest. On the other hand, if you have enough light, tungsten is a beautiful source for still life, because the spectrum has no peaks. It's quite funny, you expose a picture in what looks like horrible yellow light, and then after white balance here are these wonderful vibrant colors ... Edmund Link to post Share on other sites More sharing options...
wlaidlaw Posted October 7, 2009 Share #9 Posted October 7, 2009 The M8 also behaves pretty much the same as this in Tungsten or Halide lighting. I found that use of an Expodisc gives better results than using grey or white card for manual WB. I am guessing that the WB on the M9 is still work in progress. Think how much the auto WB has improved on the M8 since inception. It really was barely usable back in the early days (hence why I am the owner of an Expodisc). Wilson Link to post Share on other sites More sharing options...
mjh Posted October 7, 2009 Share #10 Posted October 7, 2009 Everyone has said more or less the same thing, but just for the sake of illustration – this is how the white balanced image looks in each of the three color channels: The artificial lighting has a reddish cast, with less green and much less blue. Compensating for this cast the camera amplifies the blue (and to some extent the green) channel, thereby also amplifying the noise, especially in the blue channel. That’s what is causing the yellow and blue blotches, yellow being the complementary color of blue. Link to post Share on other sites More sharing options...
jonoslack Posted October 7, 2009 Share #11 Posted October 7, 2009 Everyone has said more or less the same thing, but just for the sake of illustration – this is how the white balanced image looks in each of the three color channels: The artificial lighting has a reddish cast, with less green and much less blue. Compensating for this cast the camera amplifies the blue (and to some extent the green) channel, thereby also amplifying the noise, especially in the blue channel. That’s what is causing the yellow and blue blotches, yellow being the complementary color of blue. Thank you Michael - great . . and I actually understood that too! Link to post Share on other sites More sharing options...
wlaidlaw Posted October 7, 2009 Share #12 Posted October 7, 2009 Everyone has said more or less the same thing, but just for the sake of illustration – this is how the white balanced image looks in each of the three color channels: The artificial lighting has a reddish cast, with less green and much less blue. Compensating for this cast the camera amplifies the blue (and to some extent the green) channel, thereby also amplifying the noise, especially in the blue channel. That’s what is causing the yellow and blue blotches, yellow being the complementary color of blue. Michael, Could the camera selectively reduce noise in the blue and green channels only or is noise reduction always done on the combined RGB image? In other words, would it be possible to apply noise reduction to each channel individually in proportion to the amount which they are amplified at the analogue stage. I assume one could do this in PS by applying Noise Ninja or similar to channel layers separately and then recombining but I have not tried this. Wilson Link to post Share on other sites More sharing options...
wlaidlaw Posted October 7, 2009 Share #13 Posted October 7, 2009 I have just taken Chris's noisy image and applied NN separately only to channels green and blue. Not too effective as the blue channel was almost wholly black but here is the result. I think it might be tad less blotchy. Wilson Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/99306-m9-low-light-artificial-light-white-balance/?do=findComment&comment=1065691'>More sharing options...
chris_tribble Posted October 7, 2009 Author Share #14 Posted October 7, 2009 The artificial lighting has a reddish cast, with less green and much less blue. Compensating for this cast the camera amplifies the blue (and to some extent the green) channel, thereby also amplifying the noise, especially in the blue channel. That’s what is causing the yellow and blue blotches, yellow being the complementary color of blue. Michael - really helpful. I'll continue to experiment and see what comes up. Wilson: I have just taken Chris's noisy image and applied NN separately only to channels green and blue. Not too effective as the blue channel was almost wholly black but here is the result. I think it might be tad less blotchy. What you've done is to take the AWB image (which IMHO isn't noisy) and further corrected it. The issue here for most of us is the blue channel colour noise that Michael's identified... Link to post Share on other sites More sharing options...
jonoslack Posted October 7, 2009 Share #15 Posted October 7, 2009 Michael - really helpful. I'll continue to experiment and see what comes up. Wilson: HI Chris Have you tried it in C1? (just as a matter of interest). It needn't bugger up your workflow to use it occasionally (I do, and simply save as a .tiff file for Aperture). Link to post Share on other sites More sharing options...
melissah Posted October 7, 2009 Share #16 Posted October 7, 2009 maybe expose for the shadows? the blue channel is the culprit. try again with a bracket of 1 stop over in 1/3s. i believe jamie? wrote about exposing for shadow in noisey situs and i think hes right. id be happy to try it my self, but no m9 as of yet. best, melissa Link to post Share on other sites More sharing options...
wlaidlaw Posted October 7, 2009 Share #17 Posted October 7, 2009 Sorry Chris - finger trouble. Here it is again on the correct image to start with. I also post the blue channel to show just how noisy it is. Wilson Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/99306-m9-low-light-artificial-light-white-balance/?do=findComment&comment=1065731'>More sharing options...
dpattinson Posted October 7, 2009 Share #18 Posted October 7, 2009 I get the same blotching on the M8 at 2500, processed through C1. Link to post Share on other sites More sharing options...
chris_tribble Posted October 7, 2009 Author Share #19 Posted October 7, 2009 I've been looking at this and using the M9's bracketing to see what happens. I actually used 7 exposures at .5 stop steps - here are given in low, "correct", high sequence. First series with AWB, second series with Manual (against white card). What's happening from where I stand is that actually AWB does a remarkably good job of representing what's actually there. You've got a very yellow light source reflected from a pale grey wall and have daylight lit space further way. If you try to force the artificially lit area towards a neutral tone you end up with the daylight lit space shifting to blue. Lessons? - underexposing really pushes in noise - but we've always known that! - forcing white balance to over-correct what was really there gets you into trouble - try to work towards an honest account of the scene All we're doing with the camera is "painting with light". If the grey wall's yellow - that's how it is. Try to make it neutral grey again and you'll pay a price elswhere in the image. Sure, we can PS a pair of wings onto a pig - but it's alway going to be a pig... Final lesson - I'm hugely impressed by the M9's low light performance! If anyone wants to look at the DNGs I've posted them to http://dl.getdropbox.com/u/862415/Leica_M9/high_iso_set.zip NB - these are uploading at the moment and won't be available for perusal for a bit... Best Welcome, dear visitor! As registered member you'd see an image here… Simply register for free here – We are always happy to welcome new members! Link to post Share on other sites Simply register for free here – We are always happy to welcome new members! ' data-webShareUrl='https://www.l-camera-forum.com/topic/99306-m9-low-light-artificial-light-white-balance/?do=findComment&comment=1065818'>More sharing options...
adan Posted October 7, 2009 Share #20 Posted October 7, 2009 Chris, here is a revealing experiment to try. White-balance a tungsten-lit image using a WB for full-spectrum lighting (i.e., “Daylight” or “6000K” or whatever your sunlight default is) Open in Photoshop, and then look at the blue channel. It will be almost completely black. There are virtually no wavelengths in tungsten light that can penetrate the blue Bayer filters Kodak uses. If I really need good color balance under tungsten, and can’t substitute full-spectrum light (blue photofloods or flash), I use an 80A or similar correcting filter. As with film, it is really the only way to give the blue channel a level playing field with the red and green. Link to post Share on other sites More sharing options...
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