NX1 Block Artifacts & ISO

[لطفي بوعكاز]

I just want to share my experience with getting rid of the blocks artifacts especially on a sky, I've found out that it's all to do with ISO value! when using the gamma DR profile and a low iso this introduces very ugly blocks or artifacts on the blue channel so I tried with a high iso either 500 or 800 and turns out it reduced this by a large margin if not completely.

however high iso means overexposure, so ND filter must be used, if you're shooting a talent then you'll need to reflect light on your subject too.  The picture shows you the difference, look at top left corner, I've maximized the color grading to be able to see it. I also tried adding grain to the 100 iso image but that still didn't fix the blocky image.

The blocks are due to the compressed 8bit only video quality and the nature of h265. 

[Blah Blah]

Maybe with ISO100 it's trying to cram too wide of a dynamic range to the video.

[lucabutera]

3 hours ago, لطفي بوعكاز said:

Voglio solo condividere la mia esperienza con sbarazzarsi dei blocchi manufatti in particolare su un cielo, ho scoperto che è tutto a che fare con il valore ISO! quando si utilizza il profilo DR gamma e un basso iso questo introduce molto brutti blocchi o manufatti sul canale blu così ho provato con un alto iso o 500 o 800 e risulta ha ridotto questo con un ampio margine, se non del tutto.

tuttavia alta sensibilità ISO significa sovraesposizione, in modo da filtro ND deve essere utilizzato, se si sta girando un talento allora avrete bisogno di riflettere la luce sul soggetto troppo. L'immagine che mostra la differenza, guardare in alto a sinistra, ho sfruttato al massimo il color grading per essere in grado di vederlo. Ho anche provato il grano aggiungendo immagine iso 100, ma che ancora non ha riparato l'immagine a blocchi.

I blocchi sono dovute al 8bit compresso solo qualità video e la natura di H265. 

Do you shot this clip with NX-KS 180Mbit/s hacks?

[لطفي بوعكاز]

at 120mbps I didnt have my fast card at the time. will try again tomorrow 180mbps 

[crbellette]

Thank you!

 I have been trying to fix this problem with neat video. Not very successfully, by the way. I have a shoot next week and am looking forward to trying this out. I was about to give up on the NX1 and move to an A7Rii or another system. Thanks again for posting this.

[SMGJohn]

I got rid of the blocking issues with 140mbps although anything above that will give you CONSTANT errors saying your card is too slow despite I have the fastest card money can buy but the processor cannot keep up doing autofocus and the bitrate at the same time, if you do manual focus then you can cram it all the way up to 220mbps but 180mbps is most stable in that situation. 

[Andrew Halton]

John, at what ISO setting are you saying that you got rid of the blocking issues at 140mbps?  Thanks.

[NX1user]

I have used PNY cards since the hacks came out and they don't give me errors unless I choose 200mbps or above, they handle 180mbps fine. I have five of them and there's one that gives me that error message occasionally if the camera is cold (like 35º F or less), but it's fine once the camera has been on for a minute.

[neosushi]

On 21/02/2017 at 4:15 PM, لطفي بوعكاز said:

I just want to share my experience with getting rid of the blocks artifacts especially on a sky, I've found out that it's all to do with ISO value! when using the gamma DR profile and a low iso this introduces very ugly blocks or artifacts on the blue channel so I tried with a high iso either 500 or 800 and turns out it reduced this by a large margin if not completely.

however high iso means overexposure, so ND filter must be used, if you're shooting a talent then you'll need to reflect light on your subject too.  The picture shows you the difference, look at top left corner, I've maximized the color grading to be able to see it. I also tried adding grain to the 100 iso image but that still didn't fix the blocky image.

The blocks are due to the compressed 8bit only video quality and the nature of h265. 

Could it be the effect of the ND filter ? Some have a dark cast that (maybe ??) could explain the difference. If not its strange because this test shows that the NX1 would have more DR at ISO500 that ISO100...

[tugela]

The reason is more likely because at the higher ISO he is losing some detail in the image, which allows the compressor more bandwidth for areas which normally might be compressed to accommodate detail elsewhere, such as the sky.

Essentially by using the higher ISO value he is spreading the compression more evenly around the image rather than in specific areas. This seems to be the big disadvantage of H.265 over H.264 btw. Using higher bit rates should minimize these sorts of artifacts.