F55: Center Scan vs Full scan test with same framing

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I thought it would make sense to test the Center Scan mode and Full Scan mode on the F55 using the same framing from the two shots to really see what kind of image quality difference there might be between the two modes.

I also didn't want to switch out any lenses in order to get the same framing when switching modes as I did not want any possibility of introducing other variables which could account for image quality differences, so I only used one lens for this test and moved the camera positions in order to get approximately the same framing. I shot all these clips at f8 or higher in order to get a wider depth of field and overall sharper images from the lens.

These video clips are straight out of the camera only transcoded through FCP X in order to create ProRes video files. It is best to download them and view them on your computer. I decided not to upload them to any video sites because the added compression and softening would take away from the differences you would see straight out of camera.

Camera settings: Standard Gamma 5, 500 ISO, 0db gain, 1/48th, 23.98p, 5600k, no ND filters.

Test 1 Clips: Frozen Bush 200MB (ProRes)
(contains 2k center scan mode and full scan mode with same framing)
DOWNLOAD

Test 2 Clips: Jingle Balls 280MB (ProRes)
(contains 2k center scan mode and full scan mode with same framing)
DOWNLOAD

Conclusions: Center Scan mode is definitely not as sharp as the Full Scan mode, but center scan mode so far does not appear to suffer from any aliasing as we have seen in full scan HFR mode. Two more interesting tests would obviously be center scan HFR mode, and also shooting in 4k full scan mode then cropping out the center in post and comparing the image to the same framing shot in 2k Center Scan mode. More testing to be done.
 
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Appreciate your efforts. Went to download the first file, the frozen one and it stopped about half way through. The second one stopped about 20 to 30 megs through. Are you still uploading the files?
 
Thanks. I did finish uploading them before posting the thread and I had a hard time uploading so perhaps the uploads are rubbish. I will have to try DropBox and update the links in the morning.

In the meantime here are frame grabs from Jingle Balls. One is full scan, the other is center scan. Can you tell which is which?

tree_fullScan_zpsa258dffe.jpg


tree_centerScan_zps2454e9a7.jpg
 
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Your test setup (same focal length, same aperture, same field of view) means that the full scan image will have significantly shallower depth of field. The top one has a shallower depth of field, which means it is the full scan.

To have a fair test of scan image quality only, you have to ensure optical equivalence by using a longer focal length and narrow aperture with the full scan and a shorter focal length and a wider aperture with the center scan. Then you'll have two images with the same field of view and same depth of field, whose most significant difference will be due to the scan (full vs center).
 
noirist said:
To have a fair test of scan image quality only, you have to ensure optical equivalence by using a longer focal length and narrow aperture with the full scan and a shorter focal length and a wider aperture with the center scan. Then you'll have two images with the same field of view and same depth of field, whose most significant difference will be due to the scan (full vs center).
Click to expand...

I disagree. Changing lenses and aperture will introduce lots of variables. Dennis' methodology is correct, he just needs to shoot something flat, like a resolution test chart.
 
To me this looks to create an adequate punch in.

Very useful with the lack of cheap/fast/nice zooms.

17-55 and you are golden for runaround shoots. Very nice.

S
 
I agree the top one has a little more detail, but they are very close. Definitely close enough to use together. There is a tiny bit more compression artifact in the bottom one where the pine needles are against the grey background that isn't in the top image, but that's compression not image resolution.

My guess is also that the bottom one is the center scan.
 
Here are some tests of my own I did a couple of days ago. I don't see any difference in quality between full scan and center scan with my lenses. If I didn't add some gray bars at the top and bottom, or a post-it note in the center of the frame, you'd not even be able to see the wipe moving.

Suddenly, I have twice as many lenses in my arsenal for FREE when shooting HD or 2K. Unfortunately, I'm mostly shooting 4K these days. :-(

http://vimeo.com/82808203
 
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Duke M. said:
I agree the top one has a little more detail, but they are very close. Definitely close enough to use together. There is a tiny bit more compression artifact in the bottom one where the pine needles are against the grey background that isn't in the top image, but that's compression not image resolution.

My guess is also that the bottom one is the center scan.
Click to expand...

Good catch on that tiny bit of artifacting but I think PhotoBucket where I hosted the two frames add a considerable amount of compression so here are the original JPG's I made directly from the video:

http://www.starcentral.ca/forums/centerScan_v1/tree_fullScan.jpg
tree_fullScan.jpg


http://www.starcentral.ca/forums/centerScan_v1/tree_centerScan.jpg
tree_centerScan.jpg
 
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Doug Jensen said:
Then you don't understand what that test was intended to find out. It gave me important information that could not be discovered without the test.
Click to expand...

Well, what was that? I maybe missing something here, but as far as I could tell you rescaled the centre scan image to match the centre portion of a full scan 2K image which means you are viewing it in 1K resolution within a 2K frame. Much better to judge the centre scan at full resolution so one can properly judge resolution, noise and sharpness etc.
 
And if you would bother to actually watch my test video at Vimeo you will see that I have done exactly as you suggest . . . plus other tests also. There are four different clips, each with different things to learn from them. What's the problem?

https://vimeo.com/82808203
 
Doug, I don't have a problem. No need for the aggressive attitude. Peace and love fella.

I see you have changed the video file and added further tests - either that or I had a fault watching it yesterday as there was only the first test in that file. Either way, this latest version makes much more sense.
 
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Yes, I also think the top one looks sharper than the bottom. I did wonder at first if the higher contrast was just giving an impression of sharpness, or there was more edge enhancement, but there does seem to be more genuine detail. The more you look, the more obvious it becomes.

I also agree that for the purposes of a test it's important to know what's in the plane of focus, otherwise you can be comparing two things, find them the same sharpness - but it's because one is soft due to not quite being in focus, the other due to lower resolution of the imager.

[EDIT - and after posting I saw the comments on page 2..... Glad to see I got it right! Promise I didn't cheat.]
 
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Liam Hall said:
Doug, I don't have a problem. No need for the aggressive attitude. Peace and love fella. I see you have changed the video file and added further tests - this latest version makes much more sense. The one I watched earlier only showed only the wipe of the centre scan and never went full frame.
Click to expand...

Sorry, I don't mean to sound aggressive but it just seemed that you hadn't watched the video. I did update the video a few hours after I posted it, but that update was more than a day ago and was done BEFORE I posted anything here about it. As you say, peace and love right back at ya.
 
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No worries Doug:-) I saw the first video via the Sony Community Forum. Anyway, I appreciate the time and effort by you and Dennis creating and sharing these tests. Bottom line for me is: this is a great feature, particularly for people like me who often need to travel light.
 
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