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Post your questions for our "Ask an Engineer" event

  • 3 December 2021
  • 7 replies
  • 305 views

Topic: Image Simulation

Date: Friday, December 10th

Time: 8am - 9am PST

Engineer: Hui Chen - Senior Optical Engineer at Zemax

Join us for our first “Ask an Engineer” event! On December 10th at 8am Pacific, Hui Chen will be discussing the Image Simulation tool, and answering questions related to the analysis. This event will be hosted on the Community in text form with a focus on the spotlighted topic. 

Questions may be submitted as a reply to this thread between now and the end of the event. Once the event is concluded, the thread will be closed. 

If your question pertains to a particular file, the question may be moved to a private support case. In that situation, your license support status will be considered. 

 

Do you have a topic you want to see during these events? Let us know here: Ask an Engineer proposed topics.

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7 replies

Hui Chen
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Hi everyone! I'm online for the next hour answering your questions. Send them as a reply to this thread. In the meantime, I will address some FAQs about the tool.

Hui Chen
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Image Simulation FAQ:

Q: What is Image Simulation?

A: Image Simulation tool simulates the formation of images by convolving a source bitmap file with an array of Point Spread Functions. The effects considered include diffraction, aberrations, distortion, relative illumination, image orientation, etc. This tool helps visualize the image quality of the designed optical system. It provides a qualitative yet direct way to evaluate the imaging system performance and makes it easier for customers to “see” the simulated image quality.

Hui Chen
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Image Simulation FAQ:

Q: Image Simulation vs Geometric Image Analysis?

A: If your system is far from diffraction limited, it’s recommended you should use Geometric Image Analysis (GIA). GIA uses pure geometric ray tracing and is considered the “gold standard” for simulating an image. However, if your system is diffraction limited, you need to include the diffraction effect. In this case you should use Image Simulation. Image Simulation uses Huygens PSF to convolve with the source bitmap in order to take into account of diffraction effect. However, keep in mind that even if “Aberration: Diffraction” is selected, the analysis may still automatically switch to Geometric if the aberrations are so severe that the diffraction PSF cannot accurately be computed. The discussion on this is listed in the help file The Analyze Tab (sequential ui mode) > Image Quality Group > Extended Scene Analysis > Image Simulation

Hui Chen
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Image Simulation FAQ:

Q: What is the recommended way of using Image Simulation

A: It is recommended to define field using either Angle or Object Height when using Image Simulation tool. Use Object height for finite conjugate systems or field Angle for infinite conjugate systems, as these field types unambiguously define the size and orientation of the object in image space. Since Object Height as field definition is not allowed for infinite conjugate system, if your system has collimated input and you still want to use Object Height to define field, you could make the system finite conjugate but add a Paraxial surface in front to collimate the beam.

Hui Chen
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Image Simulation FAQ:

Q: Settings in Image Simulation

A: see help documentation for detail. Below I just highlight a few settings that we see users ask the most:

1.Oversampling vs Guard band: they both can increase the pixel resolution of the source bitmap, or in other words increase the number of pixels per field unit but using different methods. Oversampling increases the pixel resolution by copying one pixel into 2, 4, or more identical adjacent pixels, while Guard band increases the pixel resolution by repeatedly doubling the number of pixels which results in a black "guard band" all around the original image. These two options can be used when the source bitmap has a low pixel resolution, and the Guard band option is particularly useful if the point spread functions are large compared to the source bitmap field size
2.Wavelength: choosing RGB means OS ignores the system wavelengths defined in the WDE and uses 0.606/0.535/0.465 um instead for red green blue, respectively. If you want ray trace to happen at System Wavelengths defined in WDE, you’ll have to choose either 1 or 2, or 1+2+3. In that case the spot size is traced at specified system wavelengths. However, the displayed image will still be in RGB format no matter what wavelengths are defined in the WDE.
3.Aberration: When system is diffraction limited, choose Diffraction and Huygens PSF is used for convolution. When system is dominated by geometric aberration, choose Geometric for aberration.
4.PSF X/Y points: number of PSF functions generated across the whole Field of view. For field points in between these grid points, an interpolated PSF is used. Adjust this number accordingly based on the performance variation across the field. The higher the performance variation across the field, the more PSF points will be needed.
5.X/Y pixels and Pixel size: this allows you to include the effect of detector pixel resolution in the simulated image so you know if the system is limited by detector resolution. To help visualize the aberration effect, the PSF grid should cover a few pixels.
Hui Chen
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Image Simulation FAQ:

Resources on Image Simulation

1. Help documentation, The Analyze Tab (sequential ui mode) > Image Quality Group > Extended Scene Analysis > Image Simulation. This document explains all the options you see under Settings menu in the Image Simulation tool.  

2. Knowledgebase article, How to simulate high resolution images

3. Knowledgebase webinar, Simulating image quality in OpticStudio – webinar

Hui Chen
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Hi All, 

Thanks for visiting this post thread! I’ll be signing off soon but you can continue to post on this thread if you have any questions or would like to know more about the Image Simulation tool.

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