Chronos > Chronos User Discussion

Why the vertical color bands

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rdemyan:
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:
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:
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

Nikon1:
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:
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.

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