Subscriber Discussion

Digital WDR

Hi, This is my first post here. I must say IPVM is a very interesting platform for surveillance professionals, since we get an unbiased view. Thanks John.

I have a very basic question. Of late I am seeing very high values of WDR in range of 120dB (esp in cameras using Sony Effio) and they are termed as Digital WDR. What is Digital WDR and how is it different from actual WDR values we see in datasheets of reputed mfg like Bosch, Panasonic, etc.

I read somewhere that there are two types of WDR -

a) WDR achieved by double exposure: one exposure with longer exposure time to get the detail in dark area and the another is taken with shorter exposure time to get the detail in very bright area. Then the two pictures are combined in the DSP of camera to a single frame OR

b) Digital WDR which is available in low end cameras

It will be great if you guys can throw some light, so I can educate the customer to make the right choice.

First there is BLC. Which over exposes the image to reveal shadow detail at the complete loss of bright area detail.

Digital WDR is an vendor specific algorithm that boosts brightness selectively in the shadow regions of the image without overexposing the bright parts of the image. It is useful both day and night if properly implemented. However, this does not deal with reflective windows or strong sunlight.

True WDR averages a BLCed imaged with a normally exposured image to get a balanced even image. However, higher shutter speeds are needed to achieve this so night vision suffers unless its intelligently turned off at night.

From the trade show demos, Pelco's SureVision technilogy appears to be a very intelligent mix of adaptive HLC, DWDR and True WDR. It would be great if IPVM could test one of these to verify the claims.

Bohan, we tested SureVision when they first released the line. Pelco tells us a second generation is coming this year with improved performance, and we'll test that when it's available.

Neel, welcome!

In general, I would ignore digital WDR entirely as it rarely, if ever makes a practical difference. Worse, the gap in maximum performance between digital WDR and multi-exposure WDR is significant.

Finally, ignore dB ratings as they are not standardized across manufacturers and many vendors take liberties in picking very high ratings that have no correlation to their actual competitive performance.

I've found Dahua's digital WDR in their 2MP mini-domes helps somewhat in certain circumstances, but yeah, it's not something I would trust to extreme situations that would normally be handled with true multi-exposure WDR or things like Panasonic's SuperDynamic.

Point of interest: we've been using the WV-CW504 SD5 (and earlier, CW484) analog domes for the front doors on one customer's sites... however, they wanted an HD camera for their next upcoming site, so we decided to try an Axis P3384-V, since they've worked really well for their contrasty indoor lighting on the last couple sites. Will report back once that install is completed :)

Thanks guys, Security Industry is still at a very nascent stage. Educating the customer on the correct buy is extremely important. With likes of Hikvision, Dahua prevelant, it is very important that customer knows the face and take an infomed decision. Thanks guys!!!