replaced by the Siemens Star Chart which is not designed for visual As discussed in Reference 1, which may be downloaded here as a PDF file, the test chart. Star Chart, which can be run in the interactive Rescharts interface or as a fixed A detailed comparison of Siemens Star and slanted-edge MTF results is. SVG format only please, not PDF nor any of the raster formats. . then allowed me to extract a Siemens star from a PDF and start editing it.
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Below are links to six printable targets. All are sized for inch ( mm) stars. All are binary (not sinusoidal). There are three stars for Epson printers, which. A Siemens star is a device used to test the resolution of optical instruments, printers and ISO chart (pdf) resolution test chart featuring a vector siemens star; Siemens star with n= sectors for high resolution and easy calculation. We've tried basically every type of optical testing chart that exists and by There is one other test chart we find exceedingly useful, the Zeiss version of Siemens Star Chart, of John Williams, who has posted a pdf on Wikipedia Commons. . The star chart in the center of the test target makes it very easy to.
Details here. I don't know what happens with aliasing when this is rasterized for printing. For what it's worth, the PNG above was generated by the ImageMagick convert command, with default options. Star black squares in corners is the traditional design with density patches around the star and white squares inside larger black squares at the corners. No further testing is needed, go take pictures. Glad to help out. Sine, Gamma:
My purpose is to edit the SVG to vary the spoke colors from the standard black and white, for example, red on green. Not something I have tried myself, but if you plan to edit the SVG content, it might be as easy to code a star from scratch - perhaps using http: An alternative to computing the vertex coordinates for each triangle is to use the transform attribute to rotate copies of a triangle in 2. Most such programs will allow you to draw a filled triangle and copy it multiple times with rotation.
Inkscape is free open source , and uses SVG as its native format.
It seems to have the capabilities required, but I haven't used it so I don't know how easily it will duplicate and rotate the triangles you need. The tutorial puts the emphasis on interactive mousing, rather than scripting. Late last night, I managed to download Inkscape - which then allowed me to extract a Siemens star from a PDF and start editing it. I had not realized the connection between drawing software and SVG, duh.
Neither had I realized the modern use of XML to code the objects. Even at 76, I live and learn and my brain hurts. Hopes for a quick edit there faded fast. I'm probably not going to get into the scripting languages mentioned. I've already eliminated scripting from my website and just use HTML5 and that not recently how quickly I forget. I wasn't suggesting scripting for active web code. Simply figure out the description of a rotated triangle, and write copies to a file using a for-next loop or whatever equivalent construct your favourite programming language offers.
For example using https: I don't know what happens with aliasing when this is rasterized for printing. Can you speak to that issue? I have found that the aliasing algorithm is critical with things like slanted edges for SFR analysis. Not something I have looked into. In fact I only delved into the innards of SVG files in response to Ted's post today, and was pleasantly surprised at how easy it was to get something useful out. I agree that aliasing has potential for generating spurious effects.
For what it's worth, the PNG above was generated by the ImageMagick convert command, with default options. We're getting there Alan. I installed Octave, copied and pasted your script into into the editor window.
I selected Run and it told to me to save it so I did under the name "cossins". I ran again and nothing happened and no image files appeared anywhere. I ran instead a selection from the editor window. Here's what the command window says:.
If I could but fix that, I can probably run your prog. The last thing I need right now is to stop everything and start learning Octave and scripting even though it is quite interesting! I don't use the GUI version of Octave, but my best guess is that you don't have the correct filename extension. Do you know if the editor automaticaly adds a ". You may need to tell windows to stop hiding file extensions to find out.
If that doesn't work, try pasting the contents of the file directly into the command window. It should generate an output file "star.
At the very least, you should get some different error messages. It looks as though you have read the file into the command window. Do you get any other errors? What is you working directory type 'pwd' in the command window? Your screenshot shows current directory as "C: Is this where you have saved the script?
Do you have write permission in the current directory? I didn't explicitly read anything into the command window - it just appeared there after trying to Run from the editor window. That's the only error so far. I'll have to look at it later, 'cuz I'm working on a honey-do.
I see that you " ran a selection from the editor window ". The first line "! Are there any error messages below what is shown in the command window? The workspace variables have values which suggest it has run through the "for" loop the specified "cycles", so I would look for errors in the "fopen " and "fprintf " commands, or after the "fclose fid " command which flushes the output buffer and closes the output file.
Enter "pwd" to display working directory and "dir" to see what files it contains. I shall be travelling tomorrow, so apologies in advance if you post a query and I don't respond promptly.
It should be set prior to reading the image. Three settings are available as of Imatest 5. Star black squares in corners is the traditional design with density patches around the star and white squares inside larger black squares at the corners. Star registration marks on extended sides , shown on the right, is a newer design that includes registration marks and slanted-edges on the sides.
Star-only omits all extra graphics.
Just the star and nothing more. In Rescharts, select the pattern to analyze in this case, Star Chart by clicking on the appropriate entry in the popup menu below Read image file or by clicking on Read image file if Star Chart is displayed. The Read image file button and popup menu shown on the right are highlighted yellow background when Rescharts starts. Select the image to read. The ROI fine adjustment window may be maximized to facilitate fine selection. Click here or on the image to load full-size test image.
If Express mode is not selected, the input dialog box shown below appears. In Rescharts this dialog box can be at opened any time by pressing the More settings… button.
There is no setting for the number of chart cycles because it is automatically detected. Chart configuration applies to the next run. You can choose between the traditional design, which has no registration marks, or newer designs that work with automatic ROI detection. It can also be selected from the Chart configuration dropdown menu in Rescharts. Should match the chart. Affects the maximum spatial frequency of the analysis.
The inner circle consists of a registration mark quadrant pattern , which is used to refine the region alignment. Half-stars are a feature of the TE42 test chart, which will be supported by the Imatest Arbitrary charts module. Calc segments is the number of segments around the circle to display in the analysis. Select 8 the default; recommended for most work , 16, or It is no longer recommended and may be deprecated. If Calculate gamma… is selected, the 16 small square patches at the periphery of the star chart are used to determine the value of gamma for linearizing the chart, Gamma below is disabled, and the displayed value of gamma includes the indicator chart.
Gamma is used to linearize the test chart when Enter gamma… above is selected. It can be measured by Stepchart, Colorcheck, or Multicharts. If gamma is entered rather than calculated , the displayed value of gamma includes the indicator input.
MTF units, etc. Maximum x-axis frequency for linear plots selects the maximum spatial frequency to be displayed in linear plots. Star chart is the only module other than the slanted-edge modules that can analyze MTF above the Nyquist frequency 0.
Details here. You can always open this dialog box by clicking on More settings…. After you press OK , calculations are performed and the most recently-selected display appears. The Display box in the Rescharts window, shown below, allows you to select any of several displays. Display options are set in boxes that appear below Display. The spatial frequency is automatically calculated from the image, under the assumption that log frequency increases linearly with distance.
The number of chart cycles is also determined automatically. You can select between showing the first 8 segments equally weighted, or emphasizing any of the segments Segment 1 is shown as a thick black line below. The average response is a thick magenta-gray line.
Smoothed, interpolated response is normally displayed, but uninterpolated, unsmoothed raw response is available as an option. MTF is normalized set to 1. The high to low spatial frequency ratio is only 10 or 20 for the star chart — much lower than for the Log Frequency or Log F-Contrast charts. MTF should ideally be normalized to a lower spatial frequency. Case 3 should only be used with maximum contrast patterns.
MTF linear frequency scale for 8 segments of the Star pattern. Too much light can actually be a problem. We do a lot of this testing in live view mode and too much light will cause the camera to close down the aperture. Try your ambient room lighting before you set anything else up; it will probably be fine. Industrial quality fluorescent fixtures will cause the usual banding problems and should be avoided if possible. In this case a couple of incandescent or photo-quality fluorescent softboxes are inexpensive and perfectly adequate.
No computer necessary. You could use a laptop or tablet with a high-resolution monitor, or a video monitor if you have those handy. We always confirm with an actual photographic image, of course, just to be certain. Any tethered shooting setup will give you the same capabilities and can be run to a laptop or tablet.
Built-in camera Wi-Fi or a Wi-Fi card may do the same thing, as long as it gives you live-view focusing capabilities. The chart is mounted in a non-portable light housing that we use for multiple purposes. Chart, camera on tripod, and HDMI monitor are all that is necessary. Yes, you can. The first step is centering the camera. Gaffer tape or draw a line on the floor at right angles from the center of the test target.
Now as long as your tripod is centered over your line, your lens will be centered on the test target. The second step is eliminating any tilt and rotation of the camera, which is also simple. Center the tripod over the line you made at right angles to the test chart, at the spot where the test target fills the image on the monitor.
You should just see the black edges around the chart. Tilt the camera right or left, up or down so that the rectangle is squared. If the camera is tilted the rectangle will look like a trapezoid. Rotate the camera clockwise or counterclockwise so the top and bottom lines are perfectly horizontal. A degree or two of tilt and rotation is fine for this work unlike Imatest, where 0.
The camera will need a couple of degrees of clockwise rotation and a bit of turning. The first point is that we test with the aperture wide open. Even a badly decentered lens may look reasonably good when stopped down. If you have a question if this is happening, just walk around to the front of your setup and look into the lens barrel.
The star chart in the center of the test target makes it very easy to focus in live view, but first examine the pattern of the chart just out of focus at maximum magnification. On a well aligned lens the star should blur into a fuzzy oval like three of the images below do.
A badly decentered lens will blur with a flare going in one direction or another, like the image on the lower left below. This amount of flare can occur on some normal lenses, but the amount on the lower left is never normal. When you get the star sharply focused, the pattern should be circular, like the image below. In some decentered lenses the gray circle, where the individual star lines blur together will be oval.
In other types of decentering, you may notice the more vertical stars are much sharper than the horizontal stars, or vice-versa. I suggest taking a photograph with the center both in and slightly out of focus.
The idea is NOT trying to measure how well the lines resolve, especially in live view. No further testing is needed, go take pictures. When you examine them, the corners all look a bit soft, but equally so. The second step is to zoom in on one corner and manually focus the lens to bring the corner into best focus. And by how much?
Once any corner is in sharpest focus, move the cursor around to check the other three corners and see if they are all equally sharp again. Field curvature, which is a normal part of lens design, means the corners will have a different focus point than the center. But since our alignment is square and centered to the chart, the 4 corners should all focus at the same point.
As long as they do, this part of the test is normal. In reality, there are three types of misalignment: A badly aligned lens often has more than one problem and the symptoms overlap somewhat, but we can make some generalizations. A mildly tilted element often causes two corners to be different than the other two corners.
It can be side-to-side, top-to-bottom, or opposite corners. How do we tell this is simply tilt, rather than another form of decentering? With tilt, changing focus often makes the top two corners sharp, but the bottom corners will get fuzzy or left and right, etc. With other problems, the top two corners usually never get sharp, they always remain softer than the bottom corners.