Author Topic: Why the vertical color bands  (Read 5725 times)

rdemyan

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Why the vertical color bands
« on: November 17, 2020, 01:14:27 PM »
Hi:

I'm starting to use my color Chronos 2.1 and I'm having trouble with  color vertical bands. The bands are much worse when I lower the exposure time.  Because I'm using the camera for scientific purposes, I need to use a low exposure time around 50 microseconds.  But I still get the bands at higher exposure times although not as strongly. Is there something I can do to get rid of these?

julien

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Re: Why the vertical color bands
« Reply #1 on: December 11, 2020, 05:02:51 AM »
Hi,
I have the same problem on my Chronos 2.1  :(

PNG files before color grading (is it normal this purple color ?)



After color grading :





Recording 1000 fps
1080p
0dB digital / Analog Gain
180 shutter angle
Black Calibration OK
White balance 5600K

Anyone has an issue to solve this problem ?


Photopage

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Re: Why the vertical color bands
« Reply #2 on: December 16, 2020, 03:01:27 PM »
I suspect you are experiencing increased noise because you are under exposing your images.
Think about Signal to Noise ratio.
In photography the signal is Exposure. Think of the sensor noise as a constant, although external factors like heat can increase noise. 
At correct exposure the noise is not visible.  As you begin to under expose you images (reduce the signal strength) the noise becomes more visible.  If you find that you need to brighten the shadow areas of your image in Post production, you will see noise in those parts of the image, because post production adjustment increases both the signal and the noise, making the noise more visible.
Using analogue gain in the camera will help, but will also increase the noise.  Digital gain just increase signal and noise together, ie no advantage if your goal is quality.
For noise free images use more light, closer to the subject, use faster lenses and read the many posts on this forum about this subject.  If you cannot do this you will not fix the problem.

If you are sure that your zero gain image exposure is perfect, post the DNG file so others can help you assess.

The noise has nothing to do with colour issues.  Re colour, buy a grey card/ white card, use the custom white balance feature on the camera, shoot RAW and make fine adjustments in post production, or you might have to learn to love purple.

As for the chef shot,  this image is both under and over exposed in the same frame.  Unfortunately you cannot fix this image.  It was doomed from the start because of the lighting.

Some people think photography is about cameras and lenses, when the most important thing for a professional is the lighting.  This is a classic example of too much light in the specular highlight on the stainless steel sieve and not enough light everywhere else in the image.  Watch some you-tube videos on lighting techniques and have another go.  You have lots of good options here, like a side or back light, and most photographers use more than one light for a reason.

Here's a good hint, If you are standing at the mouth of a cave looking in, the light would be very similar to the chef image.  If you want the chef to look like he's in a cave, you've nailed it. 
If you want him to be in a nice bright kitchen, light the background.  If you want him in the dark, and your attention is on the stuff falling out of the sieve, then backlight the stuff falling out of the sieve, and leave the area behind the action nice and dark for contrast.

Lighting is hard, but once you start thinking about it you will see a dramatic improvement in your images.
FYI I am a professional photographer with 35 years experience and I am still learning and enjoying the challenges of making amazing images every day.  The Chronos 2.1 can make beautiful broadcast quality images, but you will need to work hard to get those images.  Not bad for the price.

Good luck!
Col


« Last Edit: December 16, 2020, 03:06:19 PM by Photopage »

Nikon1

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Re: Why the vertical color bands
« Reply #3 on: December 17, 2020, 06:02:50 AM »
Also denoising.
 I actually shot some stuff, that didnt really need denoising, but most stuff shot with the current firmware will need you to do some amount of denoising in post production if you want the absolute best possible result. This is because of the Way the Camera reads out the Sensor Data, resulting in some differences in brightness of some Vertical lines on the image. to get it looking right you however also need to put a bit of work into it, just slapping a Standard Denoise Effect on it without fine-tuning usually results in little to no effect or just blurry images. Professional Denoising Software or other editing software which can do denoising can get rid of all or most of those Lines, depending on how visible they are, and how detailed your subject is, Stuff with less details and a lot of solid colored Areas usually work best with heavy denoising, and so do Things with very clearly defined edges, things with a ton of very fine detail doesnt allways work all that well, but is mostly still better than Straight out of camera.
 .
 But i also have to Highly agree with Photopage here, Lighting and Propper Exposure (also letting the Camera Warm up bevore Shooting and Black-Calibration) will by far have the biggest impact on image Quality. You will not only need a ton of light in general usually, but also need to light your Frame evenly (Flat Lighting if you want to see everything in the image Well), or some parts of Frame will just be VERY Dark after Grading, which is (as Photopage Allready said) fine, if that is the Kind of look you are going for. But for the Darker kind of mood you would usually do backlighting or something like that.
 Apart from Lighting, I found that older Lenses with Lower Contrast work very well with this camera, because it results in an "flater" Color Profile Image than if it was shot on modern, High Contrast Lenses. Those however also tend to have a lot of flares and other Weird stuff going on, which you maybe wouldnt want to have for science Work, but can look good for Filmmaking if used right (i am using some German Lenses from the 70s, and Russian Lenses, that are even older, together with some Nikon  and Nikon-Mount -Lenses).

Nikon1

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Re: Why the vertical color bands
« Reply #4 on: December 17, 2020, 06:25:44 AM »
I had a try grading that, and just from the Screenshot you posted, i was able to fix the color mostly, and remove quite a bit of the Grain, pretty sure i would be able to get this even cleaner from propper DNG Files than from an Screenshot. Also White Balance is way easier to fix from DNG footage than Jpg (i myself usually never really bother with the In-Camera White-Balance and just Save as DNG, if its way off, i will set it roughly right to get some idea of what i am doing, but otherwise i know i will do Propper White Balance in Post anyways.). with a ton of work and Rendering time you could propably still make this look kind of ok, but i still would try to improove the Lighting. Two Softboxes in Front (Left/Right Side of camera) and At least some amount of Backlight for the Falling stuff would propably give the Result you wanted. This Camera is really sensitive about correct lighting.

Nikon1

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Re: Why the vertical color bands
« Reply #5 on: December 17, 2020, 06:37:45 AM »
Just for reference, here is a Untouched DNG from This Clip here (bevore Grading/ Denoising):
 https://forum.krontech.ca/index.php?topic=521.msg3975#msg3975  
 This was shot on an 1978 German Cine Lens.
« Last Edit: December 17, 2020, 06:39:59 AM by Nikon1 »

SergeyKashin

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Re: Why the vertical color bands
« Reply #6 on: December 17, 2020, 12:38:59 PM »
when shooting a small object, the vertical stripes are very faintly visible due to the strong background blur, but if you take something large and even in good light, the vertical stripes are very visible

Nikon1

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Re: Why the vertical color bands
« Reply #7 on: December 18, 2020, 07:04:01 AM »
when shooting a small object, the vertical stripes are very faintly visible due to the strong background blur, but if you take something large and even in good light, the vertical stripes are very visible
I dont really know what you are trying to say, i shot small and Big stuff without and With a lot of vertical lines. As Photopage explained, a lot of it comes down to propper Exposure, in other Words Sinal-to-Noise-Ratio. The DNG Above wasnt really meant as an example of a Shot without or little Vertical Lines (would have posted something else if i tried to show a DNG without Lines), since i find them to be pretty visible on that Shot in the DNG. I posted this more as a pointer to what a propper Denoising in Post can do to Images with some Lines visible in it, and this shot seems like a good example of that to me, cause the Final Clip has almost no visible lines Left, and still holds plenty of detail. Of course the Out of Focus Areas make denoising easier, because they are either solid color areas or just slow gradients (if that was what you meant?), but that doesnt really have too much to do with the initial DNGs having The Noise in them, thats from Camera Settings and Exposure. So here is a DNG with a much bigger Field of view, deeper Depth of field and almost no sign of any vertical Static noise Patterns (lines) while there is a lot of in-Focus (also even Dark) Detail.
 .
 In Summary, this post of me above was meant as a small addition to Photopages Statement, to give some Help or idea what to do, even if you for some Reason end up having some amount of lines in your Shots, to make it possible to save them if you messed up while shooting (or it was just not possible to do better in the given Conditions), or to improove good shots that still have faint noise, if you seek perfection. This is still no replacement for Propper Lighting or setting the Camera Propperly, allways try to get it right in Camera as good as you can.
« Last Edit: December 18, 2020, 07:15:22 AM by Nikon1 »

SergeyKashin

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Re: Why the vertical color bands
« Reply #8 on: December 18, 2020, 09:43:43 AM »
Comparing a street frame where the light is evenly distributed over the entire area is not very correct. I've been shooting a lot recently and I have strong bands even at 800 watts of LED light and a 1.8 aperture. They are very much visible when moving from white to darker and when removing these stripes programmatically, gives unpleasant changes on the face

Nikon1

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Re: Why the vertical color bands
« Reply #9 on: December 18, 2020, 11:19:45 AM »

 Comparing a street frame where the light is evenly distributed over the entire area is not very correct. I've been shooting a lot recently and I have strong bands even at 800 watts of LED light and a 1.8 aperture. They are very much visible when moving from white to darker and when removing these stripes programmatically, gives unpleasant changes on the face
 
 
 Ok, i think i understand now, what you mean. Its propably what i said earlier:
 
(...) to get it looking right you however also need to put a bit of work into it, just slapping a Standard Denoise Effect on it without fine-tuning usually results in little to no effect or just blurry images. (...)

 Sounds like you just slap a Denoise Effect on there, and call it a day. While you can do that for some Stuff, it wont give you the Best results possible, especially with shots like you posted.
 I would allways do at least some Layering for denoising, meaning to somehow mask out certain parts of the image, either by static position, Some Form of keying, or by brightness (as darker areas tend to show more Noise/ Lines Usually; for the Edit i did of those two frames i used all three of those), to use two different amounts of Denoising on them, a lighter denoise with more Texture on the Lighter Parts of the image, and as heavy of a denoise as you can get away with on the other parts of the Image, which you care less about or that dont hold as much detail (like out of focus Areas or the Solid colored Wall in your shot, as nobody will notice anyways, if you use a bit of detail there, as it wont be visible in the final render).
 .
 I did a quick edit on those two frames, which i assume are from the Same Sequence. because my AE doesnt like the TIFF files, i converted them to PNG in PS, and used that as a Starting Point. Those PNGs are also Uploaded with unchanged Filename, as well as the denoised Version, which has an added "(...)_EDIT" in the Filename. While those settings there in the AE Project file will work for the Whole Sequence there (assuming the Girl there stays somewhat in the middle of the Frame, put some heavy denoising on the Edges where the Vignett is), i still made two different versions of it, for each Frame, because i didnt have the Full Sequence (Settings are however the Same in both, only difference is the Frame Used).
 The Editing i did on this is pretty overkill for your everyday fun freetime shooting, but about the amount of work i would put into denoising when shooting something serious, where i care about final Quality of the Image (and this seems like some work put into it, so i assume this is some Fine Art stuff or something where this would apply).
 Since i dont know what kind of final look you are going for on this, and because i couldnt directly import the TIFF anyways (i usually shoot DNG because of this, but if TIFF works for you, thats also ok), i didnt really bother about grading or color in general for this, just some Rough White Balance-Correction in PS for the initial PNG conversion from the TIFF file. So color would propably still need some work, and maybe turn down the Sharpening a bit (depends a lot on preference, this is allready looking like a bit much sharpening for me, but other people sometimes like it to be way more agressive than that, so this is somewhere in between. for Personal use i would turn it down about 10%) for final use.
 Also posted a Screenshot for those that dont have AE, to get some idea what i am talking about.
 Hope this helps?
« Last Edit: December 18, 2020, 11:22:36 AM by Nikon1 »

SergeyKashin

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Re: Why the vertical color bands
« Reply #10 on: December 18, 2020, 03:44:03 PM »
And what does the tiff file have to do with it? I dropped the dng files. I do this too, but the skin of the face begins to suffer. I think the developers should do a little work on this and then it might get better. They also need to work with the colors of the camera because sometimes it is very difficult to correct the color even in the dng.

Nikon1

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Re: Why the vertical color bands
« Reply #11 on: December 18, 2020, 04:02:05 PM »
And what does the tiff file have to do with it? I dropped the dng files. I do this too, but the skin of the face begins to suffer. I think the developers should do a little work on this and then it might get better. They also need to work with the colors of the camera because sometimes it is very difficult to correct the color even in the dng.
Well, i just cant open the TIFF in AE, and thats the Software i use. Not that it is a bad format or something, just dont works with my workflow, and i dont plan on changing Editing Software anytime soon.
 .
 I also agree, the Color and Noise/ Line stuff can use a fair bit of improovement, but i dont quite get how this is still too much detail loss on the The Face. As i said, shapening is a bit harsh, so depending on preference turn it down a bit to get it looking more natural, but otherwise this isnt all that bad, and will propably loose more detail from Compression to delivery format anyways than from the Denoising (unless you print directly to film for High end Cinema stuff or work with some kind of actually lossless/ really high Bitrate Delivery format). Do you plan on upscaling to 4k (or more?) or something, then i maybe understand a bit where the Problem is, but for anything else i dont really get it...
 .
 Here is the same edit, but sharpening at about 1/6 of where it was bevore, so most of the way turned down.

Nikon1

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Re: Why the vertical color bands
« Reply #12 on: December 29, 2020, 03:49:39 PM »
Did some Temperature vs. Noise tests, and from what i can tell, Temperature DOES seem affect noise and Dynamic range quite a bit. I am still not done completely setting up the Watercooling for mine (need to make some more tiny Watercooling Connectors for 2mm Brass hard tubing, some are allready done), to test it propperly, so i cant say for sure yet, but that got me thinking about this topic again.
 .
 Would be very interresting to know at what kind of temperature your cameras are typically running when you get issues With Lines. Can anyone of you share some Temperatures (you can find a Sensor- and System-Temperature Readout in the Util-Menu in the About-Tab)?
 .
 When The Sensor is really hot, i also seem to get more problems With Lines, even at really good Light, on an Cold Sensor its a lot less visible with the lines. Will do some Propper Testing when i come Around to fully setting up the Cooling on mine.

Bian

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Re: Why the vertical color bands
« Reply #13 on: December 31, 2020, 12:37:13 AM »
I did some tests with a colour chart and several resolutions.

Setup: Chronos 2.1, software: unstable 20201125, Kamlan 50mm, aperture 1.1 (ful open), colour temp 5.600k, saved as TIFF

Room temperature: 21 degrees Celsius
Maximum camera temperature after 30 minutes warmup: system 47.2 degrees, sensor 46 degrees
Black calibration before the first shot and after changing the resolution
One shot was taken with 25% signal level - the other with 80 % - no colour grading
 

Nikon1

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Re: Why the vertical color bands
« Reply #14 on: December 31, 2020, 02:11:23 AM »
I did some tests with a colour chart and several resolutions.

Setup: Chronos 2.1, software: unstable 20201125, Kamlan 50mm, aperture 1.1 (ful open), colour temp 5.600k, saved as TIFF
Thanks a lot for the hint, didnt realize the new Software was available as an Unstable version yet. The New version is indeed Way better in terms of those Lines and Bands, especially for The higher resolutions (at which you would probably most care about image Quality as for Cinema and Motion Picture and such). The Bands are still somewhat there, most noticeable at higher gains, but are a lot less harsh and distracting to look at, even at the Lower exposed parts of the Image surprisingly. That means effectively a lot more dynamic range which is actually useable.
 .
Just did a very brief test, and it seems the higher Gain Settings not working at High Framerates / Low resolutions is still not fixed on that Update, but the improovement in Image Quality alone is allready huge. Also, that File Browser on there is Nice!
 Will do some more testing with that new update for sure.
 Also thanks for the Temp. Reference/ Sample Images.