Hi guys

I have an FX1E and noticed that on some high contrast edges in HDV mode, there's purple fringing. This is a phenomenon of high pixel count digital cameras. I am assuming that this is happening because of the high pixel count of the FX1's CCDs. Anyone had problems with this phenomenon?

cheers
Tim

Most reports I've read attribute this to chromatic aberration in the lens.

I have owned 2 cams lately, one the 8 megapixel Sony, the replacement is the Nikon DSLR. The Sony is infamous for it's built in additional colour. Even if you don't want it. The Larger chips and superior product blood lines of the Nikon avoid this malaise.

It seems that chromatic abberation is now part of the video camera line-up as well. Pity. Their electronics are so good.

If you call Sony to report the purple fringing they will state that this condition is normal. I've gone that route. Happily their products do retain an average re-sell value, so dumping the inferior camera was quite easy.

Your results may vary, but I have encountered this several times in the past and I am determined not to have history repeat itself at the expense of my images.

I've seen this in a few downloaded mt2 files. I did a search for "purple fringe" and it turns out it used to be a big problem with the DVX100, but if you turned Cinegamma "off" it went away. (Not sure if it's the same on the 100a or not).

If that was the case with the DVX there may be settings that will minimize this and/or post tricks to remove it (beyond avoiding high contrast shots). I have a documentary/comedy feature to shoot in September and so far for my budget I haven't found anything I like better than the FX1. My end goal is a film blow up and theatrical distribution (we can all dream, right? :)
So...
I just wonder how that purple will look blown up.


Anyone else have input on their experiences with this? I realize I may be making too much of it for a $3000 camera, but if there isn't a solid workaround I may end up renting the HVX200 and some P2 cards. (And I am in serious need of a new production camera, so renting makes me sad).

I think there are two distinct mechanisms for this type of artifact and either one, or both, may be in play.

Chromatic abberation is caused by the lens. You will see it most on the edges of the frame and should not see it at all at the exact center of the frame. If you have, for example a black tree branch against a bright sky, if it's chromatic abberation you would expect to see (for example) a green fringe on one side of the branch and red on the other side. This is caused by the lens having slightly different focal lengths for the different wavelengths (red, green, blue). There is software available for still cameras that actually reduces chromatic abberation in software, by splitting the image into red, green, and blue layers and re-scaling them to counteract the lens effects.

"Purple Fringe" on the other hand could be caused some kind of non-uniform saturation in the CCD chips, if the red, green, and blue chips may have different behaviors near the full-well point. If so, this would only be present on overexposed regions, and should go away if you just reduce your exposure, but of course if it's a bright sky that may make your intended subjects too dark.

If the purple fringe shows up even in the center of the frame, and it shows up even if you don't have over exposed areas, then I believe it must be something else other than the two things mentioned above.

Purple Fringe on the DVX was, I believe, pretty well narrowed down to overexposing cinegamma footage, and came about because cinegamma has no "knee" circuitry.

I don't think the FX1 has a similar circumstance -- its gamma curves all have knee circuits, don't they?

Seems pretty easy to narrow down the chromatic aberration theory, as the website for the EidoMedia lens modification showed that there was quite a bit less purple fringe with the Nikon lenses attached, did it not? They took the same shots with the Nikon and with the regular FX1 lens, so you could compare what difference the glass makes. If the fringe is in both shots, you could trace it to the electronics, but if the fringe appears in only one shot, it's more likely the glass.

Here's their webpage of pictures:
http://www.eidomedia.com/hdv/test/immatest/test.htm

I recently did some late afternoon landscape shots of trees on a skyline on a very windy day (Sony Z1p). The sky was 95-100% white and the leaves were dark against the sky. Looking at 2x zoom in the top right hand corner I could just make out a green / purple fringe but I mean 'just' - there is no way it would be visible with motion on a TV, in fact even on my PC monitor it is basically invisible at 100%.

Andrew

Yep the FX/Z series is prone to lateral Chromatic Aberration under certain circumstances

see forex:

http://www.moronthrottle.com/images/HDVwithcannon.jpg

thanks to Sean for the devilish little arrows :)

In fact the anamorphic expansion from 1440 to 1920 compounds the problem horizontally

I have trawled the universe for a plugin for After Effects and surprisingly none exist - so developers take note

Yep the FX/Z series is prone to lateral Chromatic Aberration under certain circumstances

see forex:

http://www.moronthrottle.com/images/HDVwithcannon.jpg



Wasn't that grab from a modified camera using a SLR lens? I thought I remember it from that.

The Sony WA lens adds some CA, here's a cropped 1:1 image of a FX-1 with the WA.
http://www.miketiffee.com/hdv/out_wide_zoomed_1to1.jpg

Here's the full image so you can get an idea of how much CA you're seeing- it's actually very small. Also, this is with the WA and with the camera zoomed all the way in.
http://www.miketiffee.com/hdv/out_wide_zoomed.jpg

Barry, thanks for clearing up the DVX issue. Also, thanks for the comparison link. I guess that means it's the glass :(

Mike, you wrote, "Also, this is with the WA and with the camera zoomed all the way in" in regards to your sample pic (thanks, btw).

So if I'm understanding correctly there is more/less fringe depending on the focal length? This makes sense in my head but I may be way off here. If this is the case, do you think there's an optimal focal length that provides the least amount of fringe?

I recently got the Z1U and to my shock I also noticed this Chromatic Abberation. Very sad.

At first I thought "how can this Zeiss T* Lens possibly be responsible?" and thought that it must be a quirk of the CCD.

Anyway it is a shame that the lens can't measure up to the 1M pixel CCDs :(

Would this show up in SD mode? In the examples I've seen the fringe is there, but very small. In SD mode there might not be enough resolution to see it. Am I correct in thinking this?

FWIW, it is rumored that Sony makes the lenses and licenses the Zeiss name, and that Panasonic does the same with Leica...

Yes, both Sony and Panasonic make their own "Zeiss" and "Leica" lenses. BUT one hopes that Zeiss and Leica design them!

And even failing that, at the very least one hopes that Zeiss and Leica approve the designs before they allow their prestigeous respective marques to be printed on those lenses! Sadly that does not seem to be the case... Presumably those German companies are more than happy with the fat royality cheques... :(

I did some test shots of purple / green fringing with my Z1p today, you can see them at:

http://www.andrew-hall-artist.com/journal/index.php?p=146

Personally I don't find it a problem to the extent it is visible.

Andrew

Great work Andrew! Very well done. I really liked the test at different focal lengths. It looks like if you hang towards the middle (and avoid shooting into the sun) you should be fine. On projects intended for film-outs this is a very easy workaround for a spectacular image. For projects not intended for a huge blow-up, I doubt anyone would even see it.

Also, I've started looking specifically for CA in downloaded clips and realized you really have to be looking to find it, and most shots don't show it at all.

There are two FX1/Z1 samples from Germany about half the way down this page -

http://www.highdefforum.com/showthread.php?t=1310

The CA is there in *maybe* three shots, which proves that 1) It IS FX1/Z1 footage and 2) I should really stop worrying about something this small. This camera can make beautiful pictures. I'm sold.

I look forward to your focus / resolutions tests. Thanks again.

Sony's purple fringing issue is much more important for still photographers - if you study a photo long enough you can find it - if it's there.

However, I defy a consumer to find "purple fringing" while watching motion video, you are noticing the action (or lack thereof) in the frame.

I have been in this business primarily broadcast for quite a while.

Could anyone really explain to me why people pay so much attention to pixel count of the CCD when it comes to small digital cameras versus the actual lines of horizontal / vertical resolution of the camera which broadcast cameras are really measured when it comes to resolution ????

Since we have all become system analysts instead of TV engineers. Remember that the TV raster in NTSC is measured in terms of lines of resolution not pixel count like a computer monitor.

Also remember that CCD pixel count sometimes is quite irrelevant because not all pixels are counted when it comes to resolution.

So I would really like to know from someone who has some TV engineering background .



Hi guys

I have an FX1E and noticed that on some high contrast edges in HDV mode, there's purple fringing. This is a phenomenon of high pixel count digital cameras. I am assuming that this is happening because of the high pixel count of the FX1's CCDs. Anyone had problems with this phenomenon?

cheers
Tim

I suppose this is a by-product of the media convergence that has seen us become adept with computer programs that transform our images to print from vector, print from raster, 3d modeling and motion graphics all in an effort to support our finished stream of pixel originated materials.
Sure the finished mpeg on my dvd is made to display on an ntsc twin field tube, but everything that occurs prior to that in the computer is completely based upon codecs and raster imagery that is pixel based for our manipulation. Since this multimedia convergence always includes more than just a dv stream, I find it extremely important to know how certain products affect my work. The purple fringing phenomenon is a mammoth blight when one is working with certain brands of digital still cameras in the prosumer price range that simply don't measure up to an acceptable standard.

Still photos are a big part of what I do. So to answer your question, the standard way of describing the digital merits of our gear has found it's common denominator. The ubiquitous pixel.

Hmmmm. Perhaps the next dv indie challenge could use "the ubiquitous pixel" as the next challenge keyword.

I don't think Tim's post was meant to really get into pixel count. I think he was just making a note that this is a problem with some high pixel count cameras, and was throwing it out there as a possible solution to the "purple fringe mystery."

If this camera shot 320 x 240 and had purple fringe, we'd be having the same conversation, IMO.

I really don't think pixel count has that much importance for video cameras. Since my old days we have measured camera resolution in lines and that's the way TV engineers still measure these days. CCD pixel count is not so relevant when measuring resolution because you have technologies such pixel offset, and many other schemes in pixel extrapolation which makes pixel count in a way irrelevant. Sure pixel rich cameras such as F900s have more pixels than Z1 camera imagers and more resolution, but that does not tell me exactly where resolution wise they both stand.

I think it is another area such as lux rating which is irrelevant when measuring the minimum illumination of a camera for comparison purposes.

And I agree with you about that this is a by-product of the media convergence. However, I would tend to think it is the wrong way to measure resolution of cameras for comparison purposes. Camera CCDs and TV rasters are not computer monitors. The NTSC equipment uses lines of resolution instead of pixel resolution. I know many programs go for the web these days instead of broadcast or playback thru a deck, but cameras are still made within the NTSC system and need to be judged as such. Have you seen a manual saying the resolution of this camera is 800,000 pixels. I don't remember. I have seen, however, camera manuals displaying the line resolution of the equipment and that's has been fairly common.

I suppose this is a by-product of the media convergence that has seen us become adept with computer programs that transform our images to print from vector, print from raster, 3d modeling and motion graphics all in an effort to support our finished stream of pixel originated materials.
Sure the finished mpeg on my dvd is made to display on an ntsc twin field tube, but everything that occurs prior to that in the computer is completely based upon codecs and raster imagery that is pixel based for our manipulation. Since this multimedia convergence always includes more than just a dv stream, I find it extremely important to know how certain products affect my work. The purple fringing phenomenon is a mammoth blight when one is working with certain brands of digital still cameras in the prosumer price range that simply don't measure up to an acceptable standard.

Still photos are a big part of what I do. So to answer your question, the standard way of describing the digital merits of our gear has found it's common denominator. The ubiquitous pixel.

Hmmmm. Perhaps the next dv indie challenge could use "the ubiquitous pixel" as the next challenge keyword.

I agree.
What will become irrelevant or obsolete is the interlaced line.
Progressive video HDTV will see to that.
Then, the manufacturers will have to pay very close attention to their pixels and quality of their imaging glass and chips.
The example noted in this thread is the first of many comparisons that will separate the good, bad and ugly no matter what the nomenclature.
That's my perception.
I have 0 experience with videotape editing. I couldn't pick out an A/B roll machine if were in a room filled with cabbages. For me, the old days were when powerpoint was displayed through a projector and somebody asked what if that were made to also play on a tv. It wasn't dazzling. Pun intended.
So far, I have been very hesitant to move from SD to HD since many of the unknown knowns aren't really known yet. What I do know is that I won't repeat the CA gaff that caught me off guard when I unknowingly upgraded to 8 megapixels for my single frame non-interlaced captures.

I always thought this was a by-product of pixel shift because the green channel is offset by half a pixel so you get a half a pixel purple edge on certain colors.

When Juan was first working on his DVX-100A adapter for uncompressed video we played around with still images from the early adapter to try and reverse the pixel shift. When the pixel shift was removed most of the purple fringing was gone.

The main difference between the DVX-100A and the Z1 is the fact that the DVX-100A mainly used pixel shift to sharpen the image. The CCD's already had enough resolution for a great image. The Z1 on the other hand is using pixel shift to gain raw resolution.

I could be wrong about this but I did notice the purple fringing to go away when pixel shift was removed.

I think the fact that you can see green / purple fringing pretty clearly indicates that this is chromatic aberration though perhaps it is exacerbated by the pixel shifting technique - which I do not yet understand (anyone got a good reference).

Andrew

I did some shots today to evaluate the Century Optics 0.6x wide adaptor (made for the DVX100) for use on the FX1. It seems to work OK, adding some barrel distortion of course.

However, in the "without wide adaptor" comparison shot I took, I can clearly see purple and green fringing where the sky is visible through the gaps in a fence, towards the edges of the frame. It is not visible in the center of the frame although the sky is just as bright there. There is a purple fringe on one side of the gap and green on the other, on the left side of the frame, with the colors reversed on the other side, and no fringe in the middle. Based on these observations I attribute this to chromatic abberation in the lens. You can see the test shot here:

http://bealecorner.net/D30/050505/03-norm.htm

I just have noticed the above by accident during some other tests.
In this pic:
http://dandiaconu.com/gallery/album05/IMGA0412?full=1
look for two square sections at the bottom of the mirror.
Left one has some minor color fringe and the right one is even worse. Same lens, same all....different contrast. Also on the rest of the image, wherever the contrast exceded the ability (for that particular speed/aperture setting) of the ccd to respond, the color fringe is there. Zebra helps.
Even the pic from the previous post reinforces (IMHO)this "confusion" (conclusion?)

Dan you have uncovered the hidden feature that is very similar to the others, apart from the usually accompanying green fringe. Whether or not this is lens or chip or otherwise electronically created, if you call the manufacturer and describe the problem they will tell you a) it's normal and b) avoid shooting areas of high contrast and to avoid low f-stop numbers.
For convenience sake, they call it CA.
I am curious with regard to the size of the frame grab. Where does 1720x1360 come from?

Jimmy, I never thought about calling them. Their answer is right (imo) and any lens behavior is the same (more on the edges). When the "feature" is in the center but under proper lighting conditions disappears, the lens is clearly not the offender... Frame size is a grab from GS200's still camera (2.3Mpix)
On the same theme, the rez chart would be better if printed on gray BG instead of white (imo) That would lower the contrast, bringing it in the CCD's ability to respond without blooming and making it more fair to judging the lens ability to resolve fine lines (if lens is questioned) rather than....oh well... about 600 lines...(just because the CCD is blooming and creating artificial edges) When the lines reach the one pixel size, the resolution is half (imo) to what the lens can deliver. Why? Because the other half is lost in the blooming of the neighboring area.
(you could see a slight resolution increase if you dim the light while shooting a rez chart)