DVX100 Artifacts, Is this normal?

Andre De Clercq · January 19th, 2003, 11:46 AM

All gamma manipulation needs ("eats") grayscale resolution. If there is not enough remaining bit depth before the DCT tranforms happens those color and grayscale clustering effects can happen (what you call macroblocks). That why pro cams use up to 16bit preprocessing before the 8 bit quantization for DV happens...

Davi Dortas · January 20th, 2003, 08:21 AM

I was under the impression that Cinegamma only affects the grayscale values. And DV 4:1:1 retains full resolution in the luminance channel. But the problems are occuring only with colours.

My test also included bringing a frame grab into Photoshop and converting it into the Lab colour mode. Looking at the individual channels revealed no macroblocking in the luminance channel but extreme blockiness in both the a and b colour channels. Footage from other camera sources did not have the same extent of the artifacts.

The fact remains that the colour channels do exhibit these artifacts and may be a result of the cinematrix settings. My GL-1 and Elura 40 do not exhibit these artifacts so it may have to do with the cinematrix settings. There wouldn't be a point comparing it against my DSR500 either. I can only assume there is a problem with the DVX100, as compared to my lower end cameras which do not show these artifacts. Having these huge artifacts seems counterproductive, if colour fidelity is hugely compromised as a result.

When I get a replacement camera, I'll post my findings.

Andre De Clercq · January 20th, 2003, 11:25 AM

Gamma correction is done on the RGB signals before YUV is being "made". To0 low bit/pixel count before gamma correction and rough (DC) Q values after DCT transformation can result in your the problems you get.

Davi Dortas · January 20th, 2003, 12:02 PM

You are probably right. Histograms in PS of my frame grabs show gaps. I never thought that to be right.

What, then, would explain why my DVX100 suffers from severe pixellations while frame grabs from other DVX100 owners seems to be fine? (and fine even from exact same tests made with my GL-1) I think my unit is faulty. The reason I posted is that all my footage exhibits these blocks, not just the rare instance. I've worked with DV material for several years, and it is the first time I have come across something like this.

Joe Kowalski · January 20th, 2003, 03:13 PM

To be fair, as Jeff pointed out, the lighting conditions of my test may have been too high contrast to bring out the problem. I will try something more subtle if I have time.

Pooja - if you do exchange your camera for a new one, let us know if it exhibits the same problem. I am hoping this is not something that affects all DVXs and I just haven't noticed yet.

Davi Dortas · February 26th, 2003, 04:34 PM

Update... five weeks later...

The problem is serious enough that both my dealer and Panasonic have offered to refund my money or keep a new camera, although they acknowledged the problem does exist and I have a choice of getting my money back.

Considering the problems I've been having with my camera I've decided to get a refund with a possibility of purchasing same camera model a year from now when I can be certain that all the bugs have worked out of this camera. I am very disappointed and all the footage that I have shot up to this point is fatally flawed.

Pooj

ps: thanks to all who have submitted screen tests to isolate this problem. Panasonic, although slow in identifying and rectifying this issue, they have been very gracious and considerate of the problems I've been experiencing.

Joe Kowalski · February 26th, 2003, 06:37 PM

Poojja -
sorry that things didn't work out. If you decide to re-buy the camera, you may want to consider a dealer such as B&H that seems to be a bit more receptive to problems like that when exchanging/refunding. Luckily, this seems to be an isolated incident... hope you have better luck next time around.

Davi Dortas · February 26th, 2003, 08:28 PM

Joe,

I returned my original camera to Panasonic. Once they found the problem, I suggested I get a replacement camera from my dealer, which I did. The problem was found on the entire batch of cameras at the dealer. Starting with serial numbers J2Txxxxxx. I was shocked. Incidentally all the cameras that the dealer had were sent back to Panasonic. Just yesterday I received word that the new batch supplied to the dealer from Panasonic exhibited the same problem but to a lesser degree than was exhibited on my original camera.

For me, that was unacceptable. They offered me the new camera but the problem was still there but to a lesser degree. (Panasonic tech confirmed over the phone)

So I finally decided to get my money back fearing that over time the problem would get worse, which would be not good.

The problem does affect more than just my camera.

Am I being too nitpicky with image quality from the DVX100? No, because my GL1, XL1, PD150 and my DSR500 do not exhibit these problems. The dealer said it may be something to do with the 24P interpolation, but I fear it's not the case.

Pooj

Skip Hunt · February 27th, 2003, 09:21 AM

I've been having some strange discoloration problems as well. I've got a fresh thread on the subject and am hoping it can be reasonably explained. However, I checked my serial number and it too starts with J2TD... J2TD00752 to be exact. Does this mean mine is definately flawed? Which vendor did you deal with?

Skip Hunt

Jason Rodriguez · March 29th, 2003, 08:27 PM

Hmmm,

I think I might have discoverd an interesting development with this thread. Pooja is having these macroblocking problems with a capture via firewire from FCP using the AppleDV Codec. The other two examples on this thread that do not show the severe macroblocking, just simple banding artifacts were captured from Vegas Video which I believe has it's own special DV Codec from Sonic Foundry as of version 3. On www.24p.com there's a comparsion between frame grabs from FCP and DVXpress, with the XPress framegrab being much smoother. These macroblocking artifacts are only in the chroma channel, and DVXPress smooths the chroma channel while AppleDV does absolutely no smoothing, it just simply repeats the color information four pixels over. I use FCP and have experienced similar macroblocking in dark areas of the frame, even though I cannot isolate these artifacts on an NTSC monitor when being played out from a deck or the camera, either via SDI or Y/C (from the camera, SDI from a DVCam deck, and although I have another thread about problems via SDI, they are not the macroblocks that Pooja is reffering to). So, is this problem a characteristic of the AppleDV codec decoding the chroma information from the DVX100? Do other cameras (PD150, GL1, XL1s) perform some sort of chroma low-pass filtering before recording to tape to elimate the 32x8 pixel chroma DCT blocks that the Panasonic does not do, and hence the AppleDV codec is showing problems since it too does not do any chroma filtering? Just something to think about.

Jason

Mark Nicholson · April 2nd, 2003, 01:00 AM

I have been able to find one, maybe two instances of this artifact happening in five hours of footage. And when it does happen, it needs Photoshop Equalize to become really noticable.

Skip, I know we got our cams at the same time, and mine is serial J2TD00561, maybe it just depends on the camera that you get and not what updates Panny has done. I would assume mine is #561 off the production line.

So does anyone have a model earlier than this or around the same time, and what are your results?

April 2nd, 2003, 01:00 AM	#26
Mark Nicholson Regular Crew Join Date: Oct 2002 Location: Eldorado Hills CA Posts: 68	I have been able to find one, maybe two instances of this artifact happening in five hours of footage. And when it does happen, it needs Photoshop Equalize to become really noticable. Skip, I know we got our cams at the same time, and mine is serial J2TD00561, maybe it just depends on the camera that you get and not what updates Panny has done. I would assume mine is #561 off the production line. So does anyone have a model earlier than this or around the same time, and what are your results? __________________ Sacramento http://eyepatchfilms.com 2x HD-250, BR-HD50, Media Composer

January 19th, 2003, 11:46 AM	#16
Andre De Clercq Major Player Join Date: Sep 2002 Location: Belgium Posts: 804	All gamma manipulation needs ("eats") grayscale resolution. If there is not enough remaining bit depth before the DCT tranforms happens those color and grayscale clustering effects can happen (what you call macroblocks). That why pro cams use up to 16bit preprocessing before the 8 bit quantization for DV happens...

January 20th, 2003, 08:21 AM	#17
Davi Dortas Membership Suspended Join Date: Oct 2002 Location: Brazil Posts: 78	I was under the impression that Cinegamma only affects the grayscale values. And DV 4:1:1 retains full resolution in the luminance channel. But the problems are occuring only with colours. My test also included bringing a frame grab into Photoshop and converting it into the Lab colour mode. Looking at the individual channels revealed no macroblocking in the luminance channel but extreme blockiness in both the a and b colour channels. Footage from other camera sources did not have the same extent of the artifacts. The fact remains that the colour channels do exhibit these artifacts and may be a result of the cinematrix settings. My GL-1 and Elura 40 do not exhibit these artifacts so it may have to do with the cinematrix settings. There wouldn't be a point comparing it against my DSR500 either. I can only assume there is a problem with the DVX100, as compared to my lower end cameras which do not show these artifacts. Having these huge artifacts seems counterproductive, if colour fidelity is hugely compromised as a result. When I get a replacement camera, I'll post my findings.

January 20th, 2003, 11:25 AM	#18
Andre De Clercq Major Player Join Date: Sep 2002 Location: Belgium Posts: 804	Gamma correction is done on the RGB signals before YUV is being "made". To0 low bit/pixel count before gamma correction and rough (DC) Q values after DCT transformation can result in your the problems you get.

January 20th, 2003, 12:02 PM	#19
Davi Dortas Membership Suspended Join Date: Oct 2002 Location: Brazil Posts: 78	You are probably right. Histograms in PS of my frame grabs show gaps. I never thought that to be right. What, then, would explain why my DVX100 suffers from severe pixellations while frame grabs from other DVX100 owners seems to be fine? (and fine even from exact same tests made with my GL-1) I think my unit is faulty. The reason I posted is that all my footage exhibits these blocks, not just the rare instance. I've worked with DV material for several years, and it is the first time I have come across something like this.

January 20th, 2003, 03:13 PM	#20
Joe Kowalski Regular Crew Join Date: Jan 2003 Location: San Francisco, CA Posts: 35	To be fair, as Jeff pointed out, the lighting conditions of my test may have been too high contrast to bring out the problem. I will try something more subtle if I have time. Pooja - if you do exchange your camera for a new one, let us know if it exhibits the same problem. I am hoping this is not something that affects all DVXs and I just haven't noticed yet.

February 26th, 2003, 04:34 PM	#21
Davi Dortas Membership Suspended Join Date: Oct 2002 Location: Brazil Posts: 78	Update... five weeks later... The problem is serious enough that both my dealer and Panasonic have offered to refund my money or keep a new camera, although they acknowledged the problem does exist and I have a choice of getting my money back. Considering the problems I've been having with my camera I've decided to get a refund with a possibility of purchasing same camera model a year from now when I can be certain that all the bugs have worked out of this camera. I am very disappointed and all the footage that I have shot up to this point is fatally flawed. Pooj ps: thanks to all who have submitted screen tests to isolate this problem. Panasonic, although slow in identifying and rectifying this issue, they have been very gracious and considerate of the problems I've been experiencing.

February 26th, 2003, 06:37 PM	#22
Joe Kowalski Regular Crew Join Date: Jan 2003 Location: San Francisco, CA Posts: 35	Poojja - sorry that things didn't work out. If you decide to re-buy the camera, you may want to consider a dealer such as B&H that seems to be a bit more receptive to problems like that when exchanging/refunding. Luckily, this seems to be an isolated incident... hope you have better luck next time around.

February 26th, 2003, 08:28 PM	#23
Davi Dortas Membership Suspended Join Date: Oct 2002 Location: Brazil Posts: 78	Joe, I returned my original camera to Panasonic. Once they found the problem, I suggested I get a replacement camera from my dealer, which I did. The problem was found on the entire batch of cameras at the dealer. Starting with serial numbers J2Txxxxxx. I was shocked. Incidentally all the cameras that the dealer had were sent back to Panasonic. Just yesterday I received word that the new batch supplied to the dealer from Panasonic exhibited the same problem but to a lesser degree than was exhibited on my original camera. For me, that was unacceptable. They offered me the new camera but the problem was still there but to a lesser degree. (Panasonic tech confirmed over the phone) So I finally decided to get my money back fearing that over time the problem would get worse, which would be not good. The problem does affect more than just my camera. Am I being too nitpicky with image quality from the DVX100? No, because my GL1, XL1, PD150 and my DSR500 do not exhibit these problems. The dealer said it may be something to do with the 24P interpolation, but I fear it's not the case. Pooj

February 27th, 2003, 09:21 AM	#24
Skip Hunt Regular Crew Join Date: May 2002 Location: Austin, Texas Posts: 37	I've been having some strange discoloration problems as well. I've got a fresh thread on the subject and am hoping it can be reasonably explained. However, I checked my serial number and it too starts with J2TD... J2TD00752 to be exact. Does this mean mine is definately flawed? Which vendor did you deal with? Skip Hunt

March 29th, 2003, 08:27 PM	#25
Jason Rodriguez Trustee Join Date: Mar 2003 Location: Virginia Beach, VA Posts: 1,095	Hmmm, I think I might have discoverd an interesting development with this thread. Pooja is having these macroblocking problems with a capture via firewire from FCP using the AppleDV Codec. The other two examples on this thread that do not show the severe macroblocking, just simple banding artifacts were captured from Vegas Video which I believe has it's own special DV Codec from Sonic Foundry as of version 3. On www.24p.com there's a comparsion between frame grabs from FCP and DVXpress, with the XPress framegrab being much smoother. These macroblocking artifacts are only in the chroma channel, and DVXPress smooths the chroma channel while AppleDV does absolutely no smoothing, it just simply repeats the color information four pixels over. I use FCP and have experienced similar macroblocking in dark areas of the frame, even though I cannot isolate these artifacts on an NTSC monitor when being played out from a deck or the camera, either via SDI or Y/C (from the camera, SDI from a DVCam deck, and although I have another thread about problems via SDI, they are not the macroblocks that Pooja is reffering to). So, is this problem a characteristic of the AppleDV codec decoding the chroma information from the DVX100? Do other cameras (PD150, GL1, XL1s) perform some sort of chroma low-pass filtering before recording to tape to elimate the 32x8 pixel chroma DCT blocks that the Panasonic does not do, and hence the AppleDV codec is showing problems since it too does not do any chroma filtering? Just something to think about. Jason