Is the GH1 too sharp? Result of hack?

UncleBenji1977

UncleBenji1977

Well-known member
I'm sorry, I don't have any examples of what I'm talking about, but I shot some footage this past weekend, and I noticed that the picture was so sharp that the fine lines had some stair stepping issues within the picture. I had the sharpness all the way down to 0. I've never noticed it being this bad before and was curious if anyone has has this issue? I don't like my picture being incredibly sharp to the point where it screams video. I like it to be a tad on the softer side of things..... Also, I don't believe I noticed this before I hacked my GH1.... I'm currently using the C settings, with my GOP set to 12, 24pN enabled. Any thoughts?
 
The anti-aliasing on the GH1 (while better than on most or all of the DSLRs that shoot video) is not optimal. That aliasing exists in the stock GH1 also. You may be noticing it now because you are looking closer, because your shots just happen to show the problem more clearly, or maybe the higher levels of compression from the stock GH1 masked the artifact a bit. Either way, the aliasing is a result of whatever process the camera is using to downsample full sensor image to a 720p or 1080p image size. It is not a result of the hack. Or at least I've seen no evidence that it is.
 
Yeah, I just had a lot of fine lines in this particular shot, and was like, "Wow."

Has anyone remedied this? Or do I just need to apply a simple gaussian blur?
 
It is pretty sharp, I end up doing a little post massaging to get rid of that, especially on faces.
 
A Gaussian blur won't fix recorded aliasing. Aliasing is the rendering of high spatial frequency detail as low spatial frequency detail. So if you blur out the aliasing, you end up bluring out good detail also.

You've already taken the first correct step. Reduce in-camera sharpening as much as possible.

But ultimately you want to reduce the excess detail getting to the sensor. That's what your camera's anti-alias filter is supposed to do. But it isn't optimized for video resolution. It's optimized for a full resolution still.

Assuming that the GH1 downsamples the full sensor image (and I'm not sure that it does, but I think it does), this is where the problem begins. Ideally, the image would be blurred appropriately and then resampled with a sophisticated algorithm. Right now my guess (based on looking at some zone plate images I've shot) is that when shooting video the camera uses a pretty sloppy but fast demosaicing algorithm in conjunction with a simple blur (low pass filter) and down-sampling algorithm (I'm guessing bi-linear or possibly bicubic). They just didn't put enough processing power into the camera to demosaic and down-sample optimally.

So in order to reduce the detail getting to the sensor in the first place, you can consider doing the following. Use a lens that isn't particularly sharp, shoot at a high f-number like f/22 (diffraction will soften the image) or perhaps slightly misfocus the lens.

Of course, aliasing isn't obvious or objectionable with all subject matter, so you'd only try those three things if you had no choice but to include those subjects. With more organic and less structured shapes, the aliasing can be beneficial in that it gives the impression of recording more detail than is actually being accurately recorded.
 
Are we talking 24p or 1080i container for 24 FPS? If it is 1080i then you might be seeing the interlaced artifacts.
 
wturber said:
A Gaussian blur won't fix recorded aliasing. Aliasing is the rendering of high spatial frequency detail as low spatial frequency detail. So if you blur out the aliasing, you end up bluring out good detail also.

You've already taken the first correct step. Reduce in-camera sharpening as much as possible.

But ultimately you want to reduce the excess detail getting to the sensor. That's what your camera's anti-alias filter is supposed to do. But it isn't optimized for video resolution. It's optimized for a full resolution still.

Assuming that the GH1 downsamples the full sensor image (and I'm not sure that it does, but I think it does), this is where the problem begins. Ideally, the image would be blurred appropriately and then resampled with a sophisticated algorithm. Right now my guess (based on looking at some zone plate images I've shot) is that when shooting video the camera uses a pretty sloppy but fast demosaicing algorithm in conjunction with a simple blur (low pass filter) and down-sampling algorithm (I'm guessing bi-linear or possibly bicubic). They just didn't put enough processing power into the camera to demosaic and down-sample optimally.

So in order to reduce the detail getting to the sensor in the first place, you can consider doing the following. Use a lens that isn't particularly sharp, shoot at a high f-number like f/22 (diffraction will soften the image) or perhaps slightly misfocus the lens.

Of course, aliasing isn't obvious or objectionable with all subject matter, so you'd only try those three things if you had no choice but to include those subjects. With more organic and less structured shapes, the aliasing can be beneficial in that it gives the impression of recording more detail than is actually being accurately recorded.
Click to expand...

Now that you say that I don't recall having too much trouble with my canon 50mm.
 
UncleBenji1977 said:
Honestly, it's whatever the hacked 24p native does. Not sure otherwise.
Click to expand...


I would to like use 24P native, however I don't trust 24PN- Not worth the risk. And i can crank the bit rate 20% higher than 24PN can do.
http://www.dvxuser.com/V6/showpost.php?p=2053448&postcount=314

Btw the latest VLC plays .mts files the best I've seen. Version 1.1.0 can play 60i and except the pull down artifacts, now longer does the image tear up and go to hell. This is good for checking material for logging etc.

Pappas
 
jleo said:
Turning up the NR also softens the image.
Click to expand...

If that is done to the image before it is downsampled, then that may provide a real help in reducing aliasing. If that step occurs after downsampling, then it isn't really reducing aliasing, it is just softening the image. At best, it is possible that it may be selectively softening the image, which may not be a bad compromise but would still be a good way from optimal.
 
I put up a post about this a month ago. I noticed the stair stepping on almost all the horizontally slanted lines in my footage when my hacked GH1 was set to 24/60i which is, of course, without native 24p checked. That was obviously interlace artifacts. But, the footage that I shot (at the exact same location of the exact same actor) with my hacked GH1 set to native 24p shows no stair stepping or interlace artifacts at all. Its just a clean, crisp, sharp image with better color rendition than the 24/60i footage. So, I've decided to continue shooting at native 24p and bitrate settings of 40,50,60. Every now and then I'll get a buggy write speed error which freezes the camera so, I know its the native 24p and not my Sandisk Extreme Class 10 card. But that usually only happens on a high detailed static shot where nothing in the frame is moving.
 
seanmcleod said:
Thats what filters are for!
Click to expand...

Agreed.

GH13 too sharp? I think it's the Panny glass that's er, hmm... too... good(?) I've experienced ultra-sharp stuff shooting with the kit lens (that I almost didn't like for the reasons given)... Try FD lenses... and/or use of a Fader on wide-to-mid lenses.

I am really enjoying the *ahem, here it comes*... film-look that I'm seeing in the GH1 with old manual lenses... the sharpness is just right for my taste.

Even the lower-rated FD lenses are looking great from what I've seen on Vimeo.
 
PappasArts said:
Btw the latest VLC plays .mts files the best I've seen. Version 1.1.0 can play 60i and except the pull down artifacts, now longer does the image tear up and go to hell. This is good for checking material for logging etc.

Pappas
Click to expand...

Ah, very interesting. I'll go get that now.
 
Put a 1/4 or 1/2 black promist on the lens, that'll take some of the digital sharpness away (should also be done with DV cameras). Another good filter is the Tiffen Soft FX1. This is especially so if you intend downconverting to Standard Definition.
 
at a certain point pushing the hardware becomes counterproductive and their is no improvement or liitle .The 24pn setting for me have not been an issue .

As I previously mentioned with the volume of experiments it is becoming apparent where the break point s of the camera's codec in hardware is.
That said however I can see where one could use specific codec setups for certain types of shoots.

For instance very low GOP with lots of I frames is in some ways spectacular but it also seems to darken and crush black levels and increase noise which is probably a direct result of pushing the hardware and codec to a place it cannot handle.
Out side in daylight this is hidden somewhat but inside or in low light it is easy to see.

The analogy is sort of like putitng twin turbo chargers on your unbluprinted engine .Ya you can produce a killer amount of horsepower for a while and get a rush out of that acceleration. but after a while you realize their is an optimum range of boost that will exist peacefully with the rest of the system of your car without changing everything.

That said I think that this camera is easily 2 to 3 time beter than was released to us

The fun will lie in amassing a list of these recommended settings for all to use .


I dont have any stock lenses...I have a combo of Canon FD, carl zeiss contax, olympus zuiko, contax G and pentax.

I is quite interesting as a person who follows photographic glass I have chosen lenses which are noted for certain special qualities. If I get some time I will post some comparitive pics and clips of some of this collection and my favourites so far. I really like all the old contax carl zeiss units...not because of their sharpness but because of their ability to single out objects an people and render tham with a real 3d contrast ...a look which they are famous for .. the Canon FD 135 F2 is also like that subjects really seem to pop out of the background ..and on the GH13 it is a 270 mm F2 that focuses to 6ft

At this point I have chosen one main lens now for all my testing of the camera at this point .
It is the contax G series 45mm .It as I have said in a previous post is highly renowned for its optical clarity etc wide open at f2 as it is essentailly a rangefinder lens

It is a pain in the A** to focus adapt but I have finally got that under control as well.

With this set known then all tests of video and still pic capabilities of the GH13 can be done with the lens basically zeroed out as an variable.

cheers guys
Larry:thumbsup:
 
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