Frans van den Bergh

Hi Rany, Some answers: 1. When you run mtf_mapper with the --chart-orientation option (I'm referring to command-line operation) it produces a file called fiducial_correspondence.txt which provides both the image space coordinates (in pixels) and the chart space coordinate (in mm) of the circular fiducial targets. The chart space coordinates are simply the expected x and y positions for a given target design, so you can use the contents of fiducial_correspondence.txt to perform any camera calibration...

Hi! Yes, this is certainly possible. Let's assume that you have mtf_mapper.exe on your PATH (see this tutorial, and you have a cmd.exe window open (or powershell). Let's also assume you have a file called sample.png (I attached one) in the current directory. Then you can run the command mtf_mapper -v 2 -q sample.png . which will produce an output file called edge_sfr_values.txt in the current directory. This file contains some comments, i.e., lines starting with a "#" symbol, which describe the meaning...

Hi Jeff, Those results are actually a textbook example of this phenomenon. To explain it briefly consider that the measured system SFR is the product of the target SFR, the lens SFR and the sensor SFR. Your experiments keep the first two terms (target and lens) constant, but changes the sensor SFR. The sensor SFR is usually approximated as |sinc(f)|, which corresponds to a box filter in the spatial domain, roughly modelling a slice through the square shape of the "ideal" photosite (note that I only...

Hi Florian, I think your calculation is in the right ballpark. So keeping in mind that one cycle = one line pair, 1500 lp/ph -> 1500/4160 = 0.3606 lp/ph. Looking at your attached sample crops, I see that your edge lengths are trending to the lower end of the range. Not a problem in itself, but if you are capturing an A4 chart from a large distance it might be (slightly) better to try and print the central A4 part of an A3 chart (on A4 paper) so that the trapezoidal shapes are a bit larger, giving...

Hi Jeff, Whoops. I hoped that QT would pick up the system properties like font size automatically, e.g., the current Windows font size. But apparently that is not the case. I'll see if I can get this to "work as expected". Thanks for reporting this! Regards, Frans

Hi Theresa, Sorry, but I don't currently have built-in support for generating charts smaller than A4. Note that this only applies to the code that generates the charts. MTF Mapper will accept and process almost any test chart that contains black squares (or trapezoids) on a white background. The lensgrid style chart adds two things: a) the edges of the squares/trapezoids are reasonably well aligned with the tangential and radial directions, while avoiding a few known bad edge orientations (e.g.,...

Right now the accuracy of the chart orientation estimation is not great outside of the range I tested; in fact it appears to be rather insensitive to rotation at other focal lengths. So unfortunately I cannot even give you a straight answer until I fix the problem, and then test with different lenses. This is a pretty big project, and I don't have as much time to work on MTF Mapper as I used to, so I won't make any promises.

Hmm. I have actually tried this before with 2 A4 prints of a modified lensgrid chart. Although this produced perfectly usable SFR measurements I found that it was too hard to align them accurately enough for the chart orientation feature to work (you actually need sub 0.1 mm accuracy). But I know Bernhard often uses multi-page prints (those are his chart designs). I'll ask him if he would mind if I include his charts with MTF Mapper. You would lose the chart orientation feature, though.