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 on: Today at 10:53:43 AM 
Started by Robert Ardill - Last post by Jack Hogan
I take it that the MTFs for diffraction (at a fixed aperture), pixel aperture and the AA filter are all constant? Also that diffraction and pixel aperture MTFs can be quite accurately estimated?

Yes, and the more you narrow the wavelength of the light the better, that's why I like to work with the green CFA raw channel only, which for some Nikon cameras has 1/2 power bandwidth of around 540nm +/-50ish.

That leaves the unknowns, which are the lens blur and AA filter.  So, if you take two shots, the only difference being a slight change in the lens blur ... could you not then work out the AA from that?  Notice that I say you, because I certainly could not!  And no doubt it's not possible to do or you would be doing it already.

Lens blur is the hardest of the simple components to model because it depends on so many variables (if we concentrate on the center only of well corrected lenses at least SA, CAs and defocus): it changes model significantly and non-linearly with even small incremental variations.  So far I have concentrated on modeling well corrected prime lenses with small amounts of defocus in the center of the FOV.  By small I mean less than half a wavelength of optical path difference (Lord Rayghley's criterion for in-focus was 1/4 lambda OPD).  It has the finickiest theory and it is the plug in my overall model: diffraction, pixel aperture and AA are set according to their physical properties and camera settings.  Solver than varies OPD to get the best fit to measured data.  There is always a residual value because no lens is ever perfect.  I  have never seen it at less than 0.215 lambda, which corresponds to a lens blur diameter of about 5.3um (on a 2.4um pitched RX100vIII).

I had a quick look at MTF Mapper and it seems very good.  If you could give me your command arguments I could use it to check my image before sending it to you.

I don't have Imatest so perhaps you can set it up to do the same thing, and trust me it would be much easier.  MTF Mapper is excellent because it allows one to work directly on the green channel raw data, without introducing demosaicing blur into the mix.  The author, Frans van den Bergh is a very smart and helpful guy whose blog got me going on this frequency domain trip. On the other hand it is an open source command line program which is not as user friendly as commercial products.  This is the way I use it, you may not want to once you realize what's involved Smiley

1) First create a TIFF of the raw data with dcraw -D -4 -T filename.cr2;
2) Open filename.tiff in a good editor and save a 400x200 pixel crop (horizontal edge, 200x400 vertical) of the central edge you'd like to analyze in a file called, say, h.tif making sure the top left most pixel of h.tif corresponds to a Red pixel in the original raw data (use RawDigger for that)
3) run the command line "mtf_mapper h.tif g:\ -arbef --bayer green -t x", assuming that you are working in directory g:\ and x is the threshold (your last two images worked with x=0.5)
4) MTF Mapper produces a number of text files and Annotate.png: open mtf_sfr.txt in Excel using the data import function.  There should be four lines with 65 values each.  The first value of each line is the angle of the edge (ideally it should be somewhere between 5-10 degrees).  The remaining 64 values are the MTF curve in 1/64th cycles/pixel increments, starting with 0 cy/px which clearly has an MTF value of 1.  Choose the line that corresponds to the edge (see the Annotate.PNG file) and plot it.

Voila', that's the MTF curve of just the two green raw channels.  Alternatively send me the file (one at a time please) and I'll do it for you - I've got batch files for most of this but they reflect how I work, call other programs and they are not easy to explain or set up if starting from scratch.


 on: Today at 10:51:55 AM 
Started by digitaldog - Last post by MarkM
Sandy, Yes, it is a brighter shade of gray in a three-dimensional space. It's chromaticity is on the axis between whitepoint and blackpoint of the particular space you are using.

Not really, unless you are confusing the CIE1931 diagram for a full description of a gamut, which it isn't. Gamuts are 3-dimensional…

Here is an effective demonstration of this point:

 on: Today at 10:47:36 AM 
Started by Dave (Isle of Skye) - Last post by Isaac
No chance. His reading skills are sub normal. He answered a question that was aimed at someone else. Sad

As you did just 2 days ago.

 on: Today at 10:45:52 AM 
Started by digitaldog - Last post by BartvanderWolf
And no, delta E cubed would NOT be a gamut measure, unless you believe that luminance is a component of gamut. (Is RGB 10,10,10 a different color to RGB 20,20,20?)

Sandy, Yes, it is a brighter shade of gray in a three-dimensional space. Its chromaticity is on the axis between whitepoint and blackpoint of the particular space you are using.

As per my post, a gamut measure would be an area measure, so a square, not a cube. Practically, if you really wanted one, an xy area from a xy gamut plot would be more useful.

Not really, unless you are confusing the CIE1931 diagram for a full description of a gamut, which it isn't. Gamuts are 3-dimensional, and one attempts to describe the perceptually relevant color differences with a delta-E cubed metric. As described in this thread, those delta-E's can be calculated in various ways, some methods are more useful (closer to actual human perception) than others, but none are perfect.


 on: Today at 10:44:12 AM 
Started by kevinweil - Last post by kevinweil
Through a process of consolidation and different storage mechanism, I have 7-10 Sawyers Rototray Carousels that I'd like to give to someone here who could use them.  Mostly they were collected in the 60s.  They work on the Kodak projector i have.  I'd just really hate to throw them out...

They look a lot like the one in this ebay listing but I'm not selling them - too much of a hassle:

All I ask is that you pay the shipping.


 on: Today at 10:38:52 AM 
Started by Mark_Seng - Last post by Mark_Seng
I use my 82mm filters (which i bought for use on the TS-E 24mm) on the PC-Distagon. They work fine. But I would not use a step-up ring from the 70mm filter thread of the lens itself.
With my PC-Distagon there came a lens hood with a filter thread with 86mm diameter. So I bought an 86mm to 82mm step-down ring. There is no vignetting which could happen with the other solution (although I am not sure, you could try).

I agree with others here that the PC-Distagon is a great lens - I love it as much as the TS-E 24mm. It's not as sharp wide open, but at f8 or f11 it's as good as the TS-E in the centre and even better in the shifted corners. There is some distortion which should be corrected for architectural use. But you can use the free Alpa Plugin for Photoshop - they have a profile that works perfect (if you have noted or can reconstruct how much shift in which direction you used).

thank you, thats very useful information.

 on: Today at 10:32:00 AM 
Started by kikashi - Last post by Bruce Cox
Nice light. I love what's going on in the left upper part of the image with the mist and the warm light on the trees.

On the other hand, I am not sure that the bottom 20% bring value.


I agree; it's beautiful.  I wonder if lower contrast in the bottom 20% would help.


 on: Today at 10:26:58 AM 
Started by digitaldog - Last post by smthopr

So yes, I think when people dismiss wide gamut working spaces to suggest 'there's no ProPhoto RGB displays' they are making a mountain out of a molehill. Just keep a steady hand on Vibrance and Saturation controls and don't keep moving them if you don't see any update on-screen. Danger Will Robinson, Danger.

Yes, exactly. This idea works in the opposite direction as well.  Why worry about using ProPhoto, when, as you've just pointed out, it's just a molehill.  At least the difference, as in your illustration, is a maximum of 5 DeltaE.

And, all one's editing decisions will be made while looking at sRGB(in this example).  My point is that the large working space doesn't effect one's editing decisions, and as you point out, is not easy to see in your example. We are in agreement, it is a molehill.  So how do you now explain this stuff to the novice?  Isn't that what this thread was about?  Because they will want to know why they need to work in a colorspace that they can't see.

 on: Today at 10:25:54 AM 
Started by JoeKitchen - Last post by torger
people made a huge cock up

Okay, I have to agree that your theory is better than mine Smiley

I realize that when you described how market speak was, I had kind of forgot about that. It's a bit symptomatic that tech cam lens performance has always been down to user testing. There were many involuntary lens switches from Schneider to Rodenstock with the P65+ to IQ180 upgrades (the IQ180 performs even worse with symmetric wides), the information was not there in advance, the users discovered it after upgrade.

 on: Today at 10:21:55 AM 
Started by ann @ nola - Last post by ann @ nola
Jferrari, yes, the cartridges are the same size and same color.  Thank you for having me check again.

John, your suggestion worked!  It only took about 30 seconds.  Thanks you for your advice. 

Ann, New Orleans

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