I was right all along, Dahua IPC-HDW4831EM-ASE - Don't follow the 4K Hype
- Thread starter Arjun
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Purple fringing is an optical flaw of a lens. It has nothing to do with video specs.
jaclarkaus
Young grasshopper
CCTVCam
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Not sure why I didn't comment on this earlier. Digital zoom should always be avoided at all costs. Digital zoom just crops an area of the picture then expands it to the size of the full frame to give the appearance of being zoomed in. In reality what you're doing is taking a small part of the picture and expanding it. To give an example, if you Digitally Zoom in to an area that's equivalent in dimensions to 1080P, then you have a picture with 1080P dimensions. When you digitally expand that out to a 4K pictures dimensions, then you halve the pixel density (reduce it by 2 as a 4K picture covers an area 2 times as large as a 1080P picture). But the the picture density in the 4K picture was 4 times the density, so you're ok yes? No. The picture also covered 2 times the area. So the pixel density was double. So, you're left with the equivalent of around a 1440P picture expanded to a 4K size. Hence the drop off in sharpness. The further you zoom the worse the picture quality gets. eg. Get down to the pixel density of 1080P, then you're expanding a 1080P picture to be 4K in size and qaurtering the pixel density in the process. Anyone who's tried this knows the drop off in sharpness in readability and increase in noise. It's this doubling of density that enables the retrieval of more fine detail in native 4K. However, the more you zoom in, the the more you reduce the density back down to 1080p or beyond....
If you need a zoom on a camera, always buy one with an optical zoom. With an optical zoom, the pixel density is maintained and should you need to retrieve detail that's small in the final picture, then you have the head room to expand it slightly to try to retrieve that detail after the fact, albeit with the same effects as zooming digitally. However, record a digitally zoomed picture, and you've already used that headroom in creating the original picture so after the fact, further cropping becomes difficult to impossible.
Please feel free to correct me if I've made an error as this is tricky to explain.
If you're upscaling from 1080p to 4K (on a 4K TV), the picture quality will obviously drastically suffer if you try to digitally zoom in. There's the general misconception when it comes to downscaling as well. You're not really getting a better picture, but albeit, I've physically seen Hikvision daytime picture quality, and the cheapest 8mp Hikvision mini bullet cameras blow the Dahua mini-bullet cameras out of the water (and I mean the cheap mini bullet camera a lot people buy and put up within the states). Its a little puzzling, because I always question why small businesses have the habit of mounting too high, but when they need to review footage they are still able to ID (in this Hikvision for example) 50 feet away. The ultimate camera should have motorized lens (similar to varifocal), but have the facility to automatically zoom in when it suspects unusual behavior (its reminiscent to PTZ, but without the complete PTZ function).
From the spec sheet the Dahua IPC-HDW4831EM-ASE is a fixed lens camera - in my experience the varifocal lens cameras (with motorized zoom and focus) always produce better quality images when you compare sensors of the same size, resolution Starvis/Starlight/Backlit sensor etc.
Taking the specifications at face value if you mount a zoomed out varifocal camera beside a fixed lens camera that says it is the equivalent value of the zoomed out varifocal lens so far there has always been a better image produced by the varifocal.
Suspicion is that the varifocal lenses are just higher quality optics so allow the image sensor to work unhindered by a cheap lens and of course the specification sheet for the Dahua IPC-HDW4831EM-ASE also says that the focus control is fixed so you will only get a truly sharp image at that fixed focus point - a varifocal automatically refocuses at power on, refocuses yet again at sunrise and yet again at sunset for day & night switchovers and if all else fails can also be manually focused - so there will always be inherent design compromises in a fixed focus lens camera compared to a varifocal lens camera.
Fixed Lens Camera Specification sheet
Taking the specifications at face value if you mount a zoomed out varifocal camera beside a fixed lens camera that says it is the equivalent value of the zoomed out varifocal lens so far there has always been a better image produced by the varifocal.
Suspicion is that the varifocal lenses are just higher quality optics so allow the image sensor to work unhindered by a cheap lens and of course the specification sheet for the Dahua IPC-HDW4831EM-ASE also says that the focus control is fixed so you will only get a truly sharp image at that fixed focus point - a varifocal automatically refocuses at power on, refocuses yet again at sunrise and yet again at sunset for day & night switchovers and if all else fails can also be manually focused - so there will always be inherent design compromises in a fixed focus lens camera compared to a varifocal lens camera.
Fixed Lens Camera Specification sheet
CCTVCam
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For some reason with down scaling the picture does seem to be better. Pixels are obviously discarded, but the pixels that remain seem to retain a greater sharpness. It's most obvious in TV where data rates are much higher than for CCTV. I'd expect CCTV to mirror it though albeit the effect might not be as obvious. I can't say I've seen downscaled CCTV. The crux to all of this is what you end up with ultimately, no matter what you do to it, comes down a lot to the quality of the source picture. If you start with low res, you get low res. If you start with High res, then even if you reduce the number of pixels or density, you still end up with something better than the equivalent with a low res source to start. To that end, optical zoom is always the way to go as digital zoom means the starting picture is always degraded in pixel density. Unless your 100% certain of the exact focal length you need for a camera, it's always worth paying the extra $10-20 for the optical zoom version.
Which is a good camera for outdoor? I have read many articles on ipcamtalk and purchase this camera from laview (LaView Saturn 4K 8MP PoE IP Turret Cameras) which is dahua 4831em-ase.
I am fine with any turret or bullet camera. Can you please recommend something with a model number as well, so its easy to search online. Laview had a good sale of selling 4831em-ase camera for around $95 each.
Thanks
I am fine with any turret or bullet camera. Can you please recommend something with a model number as well, so its easy to search online. Laview had a good sale of selling 4831em-ase camera for around $95 each.
Thanks
You can try the new 4mp 5442 Dahua Starlight turrets or the Dahua 1831E 4K Bullet. I know it may sound like I'm contradicting myself when I mention the aforementioned 4K bullet, but this 4K camera has a 1/1.8" sensor and does extremely well in low light; still does not beat Starlight models, but if you have even the slightest amount of street light this model may work well for you. Even supports 30fps, although most users here set their cameras at 15fps
It does matter depending on placement and what you're trying to capture. If this is your first camera, I would highly suggest trying a Varifocal camera instead. Anything 3.6mm and above is great for identification whereas 2.8mm is generally regarded as a general overview camera. There is the 2mp 5231 Varifocal Turret and the 4mp 5442 Varifocal bullet (both models are Starlight thus great for low light environments). With a varifocal you can adjust the focal length to your exact liking (the two aforementioned models are adjustable between 2.7 and 11mm). The varifocal models are generally more expensive however, there is a Varifocal turret model # 2231 which doesn't have on-board mic, but is a Starlight model and better than the 5231 in terms of picture quality. If you want to stick with a fixed non-adjustable lens instead, use a the IPVMv3 Calculator, you can input your address and try to estimate the appropriate focal length (it may take a while to figure out what works best using this way); I generally recommend getting a Varifocal from the get-go and working out and fine tuning things from there 
IPVM Designer / Calculator
Using Google Maps, layout and design cameras, choosing from 10,000+ models, delivering FoV and image quality previews plus export to PDF, Powerpoint and more
calculator.ipvm.com
He should have bought the 5831. I have a noname 4831 and the picture difference to a 5831 is drastic. The 5831 is the best 4k picture I have seen for something under $400. I have also seen comparisons to the 1831/2831 and it is better than either of them. Both of those are still fairly new so they may see some improvements in future firmware. They are also cheaper so maybe the components are not as good.
That's interesting. Are you doing comparisons in low-light situations, specifically in regards to capturing motion with the least amount of motion blur?
Virtually everyone's feedback has been that the larger image sensor in the 1831/2831s gives them a real advantage over the x831 models in low light. Again, when it comes to capturing motion with the least amount of blur.