Canon XH A1 Resolution Imatest MTF50

[Tom Roper]

Horizontal 730.0 lines
Vertical 659.5 lines

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http://vsdrives.com/graphics/resolut...Canon_XHA1.PNG


http://vsdrives.com/graphics/resolut...Canon_XHA1.PNG

[Tom Roper]

I used my XH A1 and Imatest software to do the above SFR (spatial frequency response) measurements. The camera settings were done on MANUAL, 60i, 1/60th, F4.8 with OIS off. The grabs are made from bitmap captures on the native m2t file. No secondary processing was performed on the bitmap image. Since the native aspect is 1440 by 1080, the MTF50 result from the chart on the horizontal has to be normalized by a coefficient of 0.75x to account for display at 1920 x 1080.

The MTF50 (Modulation Transfer Frequency) test is the most conservative method, and the one that is most commonly used for testing lens/sensor combinations. The numbers above are normalized for standard 2 pixel sharpening, so as to make the results for cams using different amounts of sharpening comparable.

Unfortunately, numbers abound on the internet, but seldom are they accompanied by the testing method used, which in its simplest form could be somebody looking at a ISO12233 chart and eyeballing 800 x 800.

More objective and still valid resolution figures could be stated for this cam as 914H lines x 792V lines by reporting the result as MTF30, and the information would be valid as long as we weren't using it to compare to a cam measured using the MTF50. So the choice between MTF50 and MTF30 has less to do with which is more valid and more to do with the goal of producing consistent results that are comparable. Since MTF50 is the generally accepted and more conservative one, that's what I use here.

[Daymon Hoffman]

Tom,

Thank you very much for your efforts.

Just a general question here. Would it be correct for one to say that the potential for HD Resolution with this camera (given your measurements) would be 481,435 pixels from a possible max perfect goal of 2,073,600 (or 23.2% of High Definition's max resolution)?

Its always confused me why some ppl say "lines" and yet everything we see on LCD's is pixels and everything thats processes is in pixels. Especially resolution. i think it was due to interlaced TV signals being measured as lines and its just carried on over. But i'd like to be clarified just to make sure i'm on the right track.

Something tells me i'm not adding it up correctly as a little under a quarter resolution of HD is what the current "HD" camera's are actually doing - just doesnt sound right. But i remember researching cameras years ago and being really unhappy with the quality (or lack thereof) and ACTUAL resolution they were giving being far lower then even the recording format's potential.

[Tom Roper]

Daymon, thank you for your kind words.

It is not correct to infer that the potential pixel resolution would be 481,435 pixels or 23.2% of HD's max resolution.

As you know, the resolution is measured in two axis, the horizontal and vertical, separately. The spatial frequency response measures LW/PH (line widths per picture height). So the first flaw in your logic is that the horizontal resolution (730 line widths per picture height) has to be multiplied by the aspect ratio (16/9) to equate to the horizontal panel size, for say 1298 horizontal pixels.

But even that doesn't tell the story. The MTF50 is the frequency of line widths (more lines = higher frequency) at which the contrast drops to 50% of the low frequency contrast. Put another way, think of the low frequency contrast as an entire screen of solid white or black. But if you break it up into vertical or horizontal stripes that get thinner and closer together, near the limits of resolution, the contrast drops as the whites and blacks move toward gray. When the gray level reaches 50%, you count the lines and that's your resolution.

But actual detail doesn't stop at the 50% contrast level. It's just the point where we stop counting lines. It's arbitrary in that sense, but a consistent method that reflects perceived sharpness.

The extinction limit of resolution goes farther to the point where you can't distinguish fine detail from noise, and it happens at the Nyquist frequency, which you can see on the plots.

[Tony Tibbetts]

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

[Daymon Hoffman]

Tom,

Thanks very much for your thorough explanation. Greatly appreciated. It will take a few reads for it to sink in (when i get the time :)). So i'll ask this question simply because i'm sure you'd have the know-how to answer (or say it simply doesnt work like that). :) I'm just wondering what would be the maximum the format *could* get to if we were to ignore things such as cost etc and say Perfection or maximum you could really expect is "this" number? To be able to compare.

The reason i wonder this is because i feel that even though there is beautiful images coming from HD cameras more and more and i'd take them over yesturdays SD stuff - there is still much further they can go. Its a lot of cash to plop down so i'd really like to get more toward the top end then not and perhaps sit out another round with a HV10 to keep me occupied. :)


Tony, i'd love to see that as well. :)

[Tom Roper]

Originally Posted by Tony Tibbetts

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

Email me a frame grab of an ISO 12233 chart and I'll run the test for any HDV cam.

[Tom Roper]

Originally Posted by Daymon Hoffman

...and perhaps sit out another round with a HV10 to keep me occupied. :)

You're in luck because I also have the HV10 which I'm going to test tomorrow night, and post the results in the HV10 forum.

I'm already certain it will do well on resolution testing, maybe even the best?

[Jack Jenkins]

So are these results good?

[Tony Tibbetts]

Originally Posted by Jack Jenkins

So are these results good?

I think any of the other comparable cameras would fare the same, but unfortunately I don't own any of the other ones to post a res chart or else I would.

Res Charts Anybody?

[Steven Glicker]

Originally Posted by Tom Roper

Horizontal 730.0 lines
Vertical 659.5 lines
...
Since the native aspect is 1440 by 1080, the MTF50 result from the chart on the horizontal has to be normalized by a coefficient of 0.75x to account for display at 1920 x 1080.

Tom, this is very interesting stuff. Thanks for the intro and sharing your results. Would you explain why are there more horizontal lines than vertical?

[Tom Roper]

Originally Posted by Steven Glicker

Tom, this is very interesting stuff. Thanks for the intro and sharing your results. Would you explain why are there more horizontal lines than vertical?

More horizontal lines on the chart, like say 973 instead of what I posted 730? Very simple. The native HDV frame grab is 1440 x 1080 but it is displayed at 1920 x 1080. So the choice is to resize the frame grab, or apply a coefficient of 0.75x (equal to 1440/1920) which is what I did.

[Tom Roper]

Soon I will be posting some interesting results on the HV10, some updated numbers on the XH-A1 that I took at the same time, and finally a definitive answer on that question everyone wants to know, "how much vertical resolution do you lose when shooting 24F."

[Jack Jenkins]

When I asked before if this was good or not, I guess more of what my very general question was asking was: Do these numbers line up with what canon has quoted for the resolution of this camera as being?

...and or what is the translation of your numbers in x and y pixels?

[Pete Bauer]

Jack, none of the camera companies, Canon included, make specific resolution claims on the video files their video cameras will create. The closest to resolution claims I've seen recently is Canon's statement that their new XL 6X lens (note: lens not whole camera) will resolve over 800 lines. They release a subset of specifications, such as pixel count on the sensors, recording format, etc. -- and in fact usually not enough of those to satisfy the more technologically inquisitive customers.

That's probably wise on the part of the companies, given the myriad ways to test cameras, and the "myriad to the myriad power" ways people choose to intrepret those tests. They leave it to reviewers and owners to determine whether the images meet their needs. So there are no rez claims to verify or refute.

For those shopping for a new camera and trying to decide, there are quite a few clips linked here on DVinfo for download and review; more are being posted all the time. Take a look and see if a particular camera's features and image suit your style and needs. If so, then arrange to put one in your hands to make sure you'll like shooting with it. Rez charts and other analyses are useful and interesting -- I do them myself -- but only tell a small part of the whole story of what a camera can do for you and whether it is one you'll be happy owning.