Sony F3 vs RED?

[Graeme Nattress]

Like these examples; Red and Moiré? - REDUSER.net ?? They're only showing a small section of the chart that goes out to 2k. The full charts (that go out to 4k) are often shown to visitors to the RED studios in full resolution so they can see the full effect.

[Alister Chapman]

Yes I've seen those. They don't go out far enough on the Red to show if it's aliasing or not in the luma, but they do show noticeable colour moire, typical of a bayer sensor starting at about 1k. If you download the image and boost the saturation a bit the colour moire becomes clearly visible.

Certainly the F35 produces strong aliasing in that example.

[Graeme Nattress]

Not seeing much in the way of any chroma moire here.

Have you shot the F3 on a zone plate yet? Be keen to see the results if you do, especially in comparison to it's big brother, the F35 which is pretty poor on the aliasing front as noted.

[Tom Roper]

Resolution can be expressed two ways. It can be expressed as pixel resolution, ie how many individual pixels can I see. Or as line pairs or TVL/ph, or how many individual lines can I see. If you point a camera at a resolution chart, what you are talking about is line pairs, or at what point can I no longer discern one black line from the next. For the black lines to be separated there must be white in between, so TVL/ph is a combination of BOTH the black and white line so will always be a lot less than the "pixel" resolution. With video cameras TVL/ph is the normally quoted term, while pixel resolution is often quoted for film replacement cameras. I believe the TVL/ph term to be prefferable as it is a true measure of the visible resolution of the camera.

There's only one extra thing that I think you may need to add to that, Alister, and it's the definition of TVL/ph - which I understand to be "TV line pairs/horizontal".

If we are talking about 1920x1080, the "pixel resolution" you talk about will be (theoretically) just that - 1920x1080. It follows that you can expect the equivalent figures expressed in line pairs to be 960 horizontally, and 540 vertically. Important thing to realise is that talking about 960lp horizontally, and 540lp vertically are both referring to lines the same distance apart on a chart - albeit at 90 degrees to each other.

Hence the introduction of lph - line pairs referenced to the horizontal. What this means is that resolving a pair of lines a given distance apart will always be given a fixed value, regardless of whether they are vertical or horizontal lines - or even diagonal. So, on the vertical axis, a resolution of 540 lp, will be exactly the same thing as 960 lph.

This all becomes especially important when charts are used with circular resolution bands, or zone plates. It means that a ring can be given a unique lph figure which is equally valid at any point around the ring.

It follows that for a 1920x1080 recording system, the maximum resolution that can be got is 960 lph. If anyone claims and sees more than that - they must be seeing aliasing.

Thanks David for adding that. One issue is that TVL/ph and Lph can be a little higher than 1/2 horizontal pixels because it is measured as the extinction point of the pair of pixels, ie the point where you can no longer see one black pixel separated from the next on the chart, so this implies that the white pixels can no longer be seen (or measured) so your actually looking at less than 2 pixels. When you measure using a scope you are looking for the point where both the white and black lines both become 50% grey That's why it is not impossible to see a measured lph resolution slightly higher than half of the pixel resolution.

Yikes! No!

TVL/ph is not "line pairs horizontal."

A TVL is either a dark line or a light line, not a pair.

TVL/ph is "TV lines per picture height." For TV it was expressed as the number of lines, either vertical or horizontal, (light or dark) that could be resolved inside a circle with a diameter equal to the vertical dimension of the frame.

1080 is Nyquist, not 960.

TVL resolution can be expressed at MTF50, or any other level between 0 and 100%. The resolution number varies accordingly.

For photographic lenses and film, resolution can be expressed as lp/mm, line pairs per millimeter.

I'm sorry for interjecting here, and if you feel I'm wrong feel free to correct me. I'm not sure how it affects the discussion for 4k/2k/1k bayer filters, but the term TVL/ph has a defined meaning. The use of TVL/ph (tv lines/pic height) is helpful because it removes the aspect ratio of the frame size from being a factor in the discussion of horizontal resolution versus vertical resolution.

If you had perfect theoretical resolution for a 1920x1080 sensor, you would have 1080 TVL in both axis, but you would measure 1920 lines across the frame width.

[Alister Chapman]

Thanks for jumping in and putting us straight.

I don't think it changes the argument. But good to have the terms corrected. Of course while TVL/ph is as you say individual lines, to be able to see one line form the next you do have to be able to see or measure the complimentary line. Not sure how you would express MTF below 50% as once you get down to 50% grey any further MTF reduction would just be more of the same 50% grey, unless I've missed something?

If you boost the saturation a little of the zone plates on the Red site the colour moire is plainly visible. I have not yet seen a zone plate from an F3 it will be interesting to see.

[Graeme Nattress]

If you take your zone plate and plot a scanline you'll see a series of sine waves increasing in frequency and decreasing in amplitude from the centre out. Although printed with equal amplitude, the imaging system will see them with reducing amplitude - this is the MTF of the system.

If we call the largest peak to peak amplitude on our plot 100%, we can travel down the sines of increasing frequency until we get a peak to peak amplitude of 50% (of our largest amplitude) and now we've found out MTF50 point. At this frequency we're still seeing a strong MTF and a good figure for frequency here will appear visually as a sharp image. If we keep on going until our peak to peak is 0%, we now have mid-grey and no detail at all, although for limiting resolution I'd probably call it below ~10% as it gets hard to tell below that.

Graeme

[Alister Chapman]

I know Graeme, I was getting muddled by Toms references to both MTF50 and 50% grey in the same sentence. I was referring to the fact that once you get down to 50% grey (the extinction point) the frequency response becomes zero so can't be measured, or at least there is nothing to measure. So MTF50 is before you get to 50% grey. Getting muddled, as zero contrast which is zero MTF normally means 50% grey, assuming the lines or rings were originally at 100% and zero.

Doh.. head hurts. You have to be so careful how you read and how you express all this stuff.

[Graeme Nattress]

It's tricky when you're dealing with 50% MTF's and mid (50% grey), but mid grey is when you get to 0% MTF :-) It's so much easier to show visually rather than in textual comments.

One nice thing you can do with your circular sine zone plate is plot MTF, and also you can look at the area under the MTF curve which strongly correlates with what we perceive as overall image sharpness.

Graeme

[Tom Roper]

Gray (half way between white and black) would be extinction, 0% MTF.

I'm sorry, I didn't think that through. Thanks for the correction.

[David Heath]

My own references were to lph, which I understood to be "line pairs/horizontal", and shouldn't really be confused with terminology along the lines of TVLetc.

In other words, for a 1920x1080 image, the reference is to 1920 LINES res horizontally ("either a dark line or a light line, not a pair") OR 960 LINE PAIRS. (Being able to resolve a white/black pair of lines.)

My understanding is that it's relevant as this is what most res charts are nowadays marked in? With the outer ring of an HD chart typically 1000 lph? If the scale was TVL/ph (tv lines/pic height), it would be given the value 2000.

[Tom Roper]

This is a little tough to write from my Blackberry, but here goes:

Lph still refers to lines per pic height, not line pairs horizontal. LW/PH, LPH, TVL are all really expressions of the same quantity, lines not pairs.

400 TVL would mean if you had a 4x3 tv set, you would measure 200 black and 200 white lines from east to west over a length equal to the north-south dimension.

LPH is saying the same thing.

ISO 12233 charts for digital still cameras use LW/PH for the scale.

Analog tv EIA-1956 charts use TVL, but they are the same as LW/PH or LPH.

TVL is always stated as horizontal resolutiion, dating back to interlaced broadcast, where the vertical rez can be no better than the number of horizontal scan lines.

For progressive images, it's valid to state the vertical resolution the same way, TVL or LPH.

For film and photography. LP/mm (line pairs per millimeter) is sometimes used.

You can sometimes find a spec for Sony HD cams where they state the resolution as 1000 TV Lines. What that's saying, is you should be able to count 500 black and 500 white, vertically oriented lines, over a horizontal distance equal to the vertical dimension. That would also equate to 1778 lines if you counted them across the full width of the panel, and I suppose 889 line pairs to your way of counting.

[Peter Moretti]

Originally Posted by Alister Chapman

...
Putting that into Red One perspective, it has a sensor with 8 Million pixels, so the highest possible sample size would be 8 million samples. Red Epic 13.8 million. But it doesn't stop there because Red (like the F3) use a Bayer sensor where the pixels have to sample the 3 primary colours. ...

Alister,

Where are you getting that 8 Megapixel number from? Perhaps the old sensor? The latest Red One (MX) is 13.8 megapixels, FWIU.

CAMERAS / RED ONE

[Alister Chapman]

Yes that was for the old sensor. If I had meant MX I would have said MX. Still doesn't change the fact that Red like to boast about pixel count as resolution, which it is not. Yes MX should achieve higher resolution than the old sensor but it doesn't make it a "5k" camera in the true sense of the meaning. Working on the Red principle Sony, Panasonic etc could claim a 1080 camcorder to be "2k" near as damn it, but they don't. All the headline talk of megapixels does is create confusion as you have to factor in many other things, including sensor type, pixel offsets etc.

[Peter Moretti]

Alister,

Come on, this is really not being fair to Red. First off, the Red One currently comes with the MX sensor. So you've been talking about a sensor that the camera does not even come with anymore. And owners with the old sensor can upgrade to the new one; MANY have.

But more than that, anyone w/ $25K to spend on a camera should pretty quickly be able to understand that Red is quoting the horizontal pixel count of the image area. They claim the actual measured luma resolution is about 3.2K. And any resolution chart you can pin up is going to show that the Red has significantly more resolution than any other digital camera. Please show an example if I'm wrong.

Where I do find Red misleading is the 4:4:4 claim. It's interpolated 4:4:4. You can claim "4K" or you can claim 4:4:4 at a lower resolution, but Red really can't claim both. If chroma resolution is less than luma resolution, then it's not 4:4:4.

[Chris Hurd]

Let's be fair please. Any discussion of RED One should refer to its current shipping configuration which is in fact the MX sensor.