Canon XH A1 Resolution Imatest MTF50

[Tom Roper]

Ditto what Pete said. You don't use these numbers alone to base a camera decision on, and since you're looking for resolution to be stated as a translation of x pixels and y pixels, you don't have enough of an understanding of resolution measurements to be anything other than mislead by them if you did. That's not a knock. Thousands of consumers make purchases every day based on resolution stated as pixels. This HDTV has 1080p resolution, or this one has 1920x1080 resolution. That's just the native panel size Jack. The resolution of detail is always something lower, and it's expressed very differently in any case.

For example, horizontal resolution numbers always seem low. A panel has 1920 horizontal pixels. How come I only get 800 lines horizontal resolution from this cam? For one thing, resolution is most often expressed in line widths per picture height. In other words, the lines that can be resolved are only counted in the horizontal direction for a distance equal to the height of the screen. If you counted 810 of them this way, the number seems low but you would be at the Nyquist limit of the HDV format, i.e. nothing left to be had. Multiply 810 times the aspect ratio 16:9 (1920/1080), and you come up with 1440 lines, which is the Nyquist limit for the format. You may still be able to count more lines but beyond the Nyquist frequency they are just a form of noise or aliasing.

The Nyquist limit for HDV expressed as LW/PH is 810x1080. As lines get closer together, black and white begins to blur toward gray. The MTF50 spec (Modulation Transfer Frequency) says that we stop counting lines when the contrast level gets to 50% (gray). Other measurements of resolution will extend farther, but we need one that is standardized and agreed upon. The MTF50 is pretty universally accepted. But that doesn't stop someone from saying, "hey I see more lines than that just by looking at the chart!" MTF50 most arguments if the testers just agree to use it, which most pro testers do, but I've seen plenty of numbers thrown around where you know they are just eyeballing a chart that's been photographed. A result could be off by 100 lines doing that, not precise enough!

Consider this, you have a new HDTV with 1920x1080 panel size. You project a computer generated image of 960 horizontal black bars, and 480 vertical black bars against white screen backdrop. At best what would it look like? A checkerboard if you're imagninative, or simply a noisy gray picture.

[Tom Roper]

810.0 Lines Horizontal
660.4 Lines Vertical

I've duplicated this result over and over now, nothing further to be gained. Basically it's this, the MTF50 test easily returns Horizontal lines at 825-850, but the Nyquist frequency is 810, therefore the result gets capped at that. The layman's explanation is that the cam easily maintains more than 50% contrast all the way to the limit of the HDV format in the horizontal direction, excellent.

In the Vertical direction, there's more potential in the HDV format than this cam is yielding.

For comparison, the Canon HV10 has the following resolution relsults:

784.5 Lines Horizontal
704.8 Lines Vertical

Nearly an identical performance in the horizontal to the XHA1, and significantly better on the vertical. The actual measured vertical resolution on the HV10 was only 624.0 lines whereas the actual measured on the XHA1 was 665.9, but when the results were normalized to equalize differences from in-cam sharpening, the HV10 got a nice bonus and the XHA1 received a 5 yard penalty.

And what about Canon 24F Mode on the XHA1?

810.0 Lines Horizontal
590.4 Lines Vertical

...so the 24F penalty is a resolution loss of 10.6%


http://vsdrives.com/graphics/resolut...Horizontal.png
http://vsdrives.com/graphics/resolut...1_Vertical.png
http://vsdrives.com/graphics/resolut...Horizontal.png
http://vsdrives.com/graphics/resolut...0_Vertical.png
http://vsdrives.com/graphics/resolut...zontal_24F.png
http://vsdrives.com/graphics/resolut...rtical_24F.png

[Holly Rognan]

Thanks for spending the time to do this. Many people are very interested in this, and you have put the issue to rest. Some people have claimed a 50% loss for frame mode, others stating probably 20%-30% was more realistic, but to hear that it is only 10% is very impressive.

Either way, I am impressed everytime I use 24f. I wouldn't care if it was a 50% loss, the picture it creates is a phenominaly crisp, larger than life expression of reality.

[Jack Jenkins]

So the single chip HV10 has a higher resolution image than the XH-A1? What gives? 3 native 16 x 9 1/2" CCDS and giant 72mm lens are not resolving more information than a single 1.27" CCD behind a dime sized 37mm lens? Is it the CMOS or what?

[Daymon Hoffman]

Tom, Thanks so much for doing the HV10. What an amazing little camera (what a shame we always get a "pick two of the three" style thing with cameras these days). Perhaps i shall get one in leiu of XH-A2 ;)

NB: out of interest i'd love to see a digital camera shoot native 1080p and have this same test done to see what resolution it yeilds. Shouldn't that be the top limit of 810 etc?

[Jacob Mason]

Originally Posted by Jack Jenkins

So the single chip HV10 has a higher resolution image than the XH-A1? What gives? 3 native 16 x 9 1/2" CCDS and giant 72mm lens are not resolving more information than a single 1.27" CCD behind a dime sized 37mm lens?

Actually, the A1 has 3x1/3 CCDs, and the HV10 is a single CMOS chip.

[Jacob Mason]

BTW Tom, thanks for taking the time to do these tests and providing us with the results.

[Pete Bauer]

Originally Posted by Jack Jenkins

So the single chip HV10 has a higher resolution image than the XH-A1?

No, in good light with a static test image, it is about the same -- measured at slightly more in one direction, and slightly less in the other direction. As mentioned earlier, there's SO much more to a camera than static horizontal and vertical resolution. They are important things to know, but these cameras provide very different trade-offs for real world use. The HV10 is tiny so it can go anywhere. The XH cameras have much better low light capability and a plethora of ways to control the image and even change the way some of the camera buttons and controls work.

And Tom, let me add my thanks as well for your efforts here.

[A. J. deLange]

Originally Posted by Tony Tibbetts

I'm curious to know how the comparable cameras would do in this sort of test.

I posted MTF curves for three lenses for the XL-H1 several months back. They are at http://www.pbase.com/agamid/image/54766171. Note that the axis is in cycles per picture height (the appropriate units) and that this camera turns in about 350 cycles at 50%. If you consider a half cycle to be a line, which most people tend to do even though it is one side of a sinusoid, this camera would be said to have about 700 lines of resolution.

The reason there is response beyond the Nuyquist frequency (405 cycles) is because the picture is upsampled (in the camera) to 1920 horizontal pixels corresponding to 1080 pixels pph for a Nyquist of 540 cycles pph and then sharpened. The plot at http://www.pbase.com/agamid/image/54766057 shows the reconstructed edge from an ISO 12233 chart which clearly shows this sharpening (the under and overshoots). I expect that the explanation is the same for the cameras being discussed in this thread. Put simply, some of the resolution you see isn't really captured by the camera. But it looks real and results in a breath taking picture so who cares?

Another caveat with MTF is that a measurement or two doesn't tell the whole story. It needs to be measured radially and tangentially at several azimuths and cone angles and at different focal lengths and apertures. It is most interesting that Canon has a web site with extensive MTF data on all their lenses - except the ones that go with their prosumer video cameras. Granted most, if not all, of this data is computed rather than measured but still at least it's data.

PS: The F in MTF stands for 'Function' - not frequency.

[Mathieu Kassovitz]

Originally Posted by Jacob Mason

Actually, the A1 has 3x1/3 CCDs, and the HV10 is a single CMOS chip.

Actually, it would be particularly interesting to test the resolution with the shutter at 1/25:

http://www.dvinfo.net/conf/showthrea...671#post579671

True 25p outcome? Or will the resolution drop? Would it be substancially?

*EDIT*Link now fixed.

[Peter Ferling]

Originally Posted by Pete Bauer

No, in good light with a static test image, it is about the same -- ... but these cameras provide very different trade-offs for real world use. The HV10 is tiny so it can go anywhere. The XH cameras have much better low light capability and a plethora of ways to control the image and even change the way some of the camera buttons and controls work.

And Tom, let me add my thanks as well for your efforts here.

Well said Pete. I love the image from my Sony HC1 (and HDV camera), but there are jobs were I've fallen back to my old XL1s (an SD camera) for better controls to get the shot because resolution isn't everything. With the G1 I'll get the best of both worlds.

Thanks also to Tom. I'm set on getting a G1.

[Terence Murphy]

Originally Posted by Tom Roper

And what about Canon 24F Mode on the XHA1?

810.0 Lines Horizontal
590.4 Lines Vertical

...so the 24F penalty is a resolution loss of 10.6%

Thanks for the detailed measurements, especially starting to look at frame mode. Any ideas on how to measure the effect of frame mode on vertical resolution in areas of motion? Maybe using shots from a slow horizontal pan across the resolution chart? You'd probably need a true-progressive scan camera to use as a control (show that with the same movement the progressively scanned image doesn't lose vertical resolution, but the frame-mode image loses xx% compared to no movement).

I would expect the frame-mode voodoo to have a harder time maintaining vertical resolution for areas of motion. Of course, if most of the image is static and resolving at almost 600 vertical lines, it'll still make a pretty picture even if your moving subject is at a lower actual resolution. The penalty is probably larger when the camera moves.

-Terence

[Tom Roper]

Warning Will Robinson!

But just to add a few more observations:

1.) Not unlike Canon DSLRs, "L" series lenses won't always outperform a cheaper standard lens at a given selected aperture, say F5.6 or F8.0, but what does seem to be true about them is that the L's give even consistent performance across a range of focal lengths, zoom ranges and uncompromised at the larger low light aperture openings. That is my observation about the 4.5-90L XHA1 lens as well.

2.) I tested the XHA1 at different combinations of zoom range and aperture to find the limits where performance falls off. Of course, I did not try different focal lengths because that requires moving the actual camera to target distance, which in all of the tests was 78 inches. The gain level was 0 db. All frame grabs are "I-frames."

3.) At the 78 inch focal length, I was able to test the zoom range from about 4.5-40mm, or about 0-40% of the zoom range. The performance across this range (9 to 1 zoom!) was very even, with a slight sweet spot at about the 15% mark.

4.) As A.J. Delange points out, a measurement or two doesn't tell the whole story, measuring radially, tangentially, different azimuths and cone angles etc., is needed. I performed just one, the slanted edge test, and only for the center area of image, but I did it as precisely and consistently as I could.

Let's get on with the conclusions!

5.) The range of apertures yielding the generally highest resolution results is F3.2-F4.8, with F4.0 as the sweetspot.

6.) As mentioned earlier, performance is very consistent across the zoom range of 0-40%, with 15% zoom mark being the sweet spot for resolution.

7.) There are all the usual reasons for deviating from these ranges, depth of field control being one, CA generally being less at the smaller aperture openings, (F5.6+).

...and then this observation:

8.) In-Cam sharpening, where do think you have it set? Because from my inconclusive observations, it appears not to be a static amount but changes dynamically with aperture and *gain*, the intent I would infer to maintain the same generally perceived sharpness at low light, high gain, large aperture opening that the viewer would observe in bright light, low gain, small aperture opening. The cam would appear to maintain really sharp detail in low light conditions compared to other HDV cams I've used.

I appreciate the many thanks expressed, but my motivation is that you get something positive and find the information useful for your own purposes.

Tom

[Thomas Smet]

One way you could test motion resolution is to use the remote control to zoom in and out. You could do it once as 60i and the second time as 30F and then match up the same exact moment in time and test the resolution.

I'm not sure how the results would turn up because video in motion has lower detail anyways due to motion blur and a lot of other things. Even if resolution of 24F and 30F drops a little bit more during motion does it really matter?

[Tom Roper]

Originally Posted by A. J. deLange

The reason there is response beyond the Nuyquist frequency (405 cycles) is because the picture is upsampled (in the camera) to 1920 horizontal pixels corresponding to 1080 pixels pph for a Nyquist of 540 cycles pph and then sharpened.

Thank you! I was definitely hoping someone could/would answer that.

I look forward to spending some time reviewing the links you posted to your own tests.