July 26, 2014

Lens testing at Elphel

by Andrey Filippov

We were measuring lens performance since we’ve got involved in the optical issues of the camera design. There are several blog posts about it starting with "Elphel Eyesis camera optics and lens focus adjustment". Since then we improved methods of measuring Point Spread Function (PSF) of the lenses over the full field of view using the target pattern modified from the standard checkerboard type have better spatial frequency coverage. Now we use a large (3m x 7m) pattern for the lens testing, sensor front end (SFE) alignment, camera distortion calibration and aberration measurement/correction for Eyesis series cameras.

Fig.1 PSF measured over the sensor FOV

Fig.1 PSF measured over the sensor FOV – composite image of the individual 32×32 pixel kernels

So far lens testing was performed for just two purposes – select the best quality lenses (we use approximately half of the lenses we receive) and to precisely adjust the sensor position and tilt to achieve the best resolution over the full field of view. It was sufficient for our purposes, but as we are now involved in the custom lens design it became more important to process the raw PSF data and convert it to lens parameters that we can compare against the simulated achieved during the lens design process. Such technology will also help us to fine-tune the new lens design requirements and optimization goals.

The starting point was the set of the PSF arrays calculated using images acquired from the the pattern while scanning over the range of distances from the lens to the sensor in small increments as illustrated on the animated GIF image Fig.1. The sensor surface was not aligned to be perpendicular to the optical axis of the lens before the measurement -each lens and even sensor chip has slight variations of the tilt and it is dealt with during processing of the data (and during the final alignment of the sensor during production, of course). The PSF measurement based on the repetitive pattern gives sub-pixel resolution (1.1μm in our case with 2.2μm Bayer mosaic pixel period – 4:1 up-sampled for red and blue in each direction), but there is a limit on the PSF width that the particular setup can handle. Too far out-of-focus and the pattern can not be reliably detected. That causes some artifacts on the animations made of the raw data, these PSF samples are filtered during further processing. In the end we are interested in lens performance when it is almost in perfect focus, so scanning too far away does not provide much of the practical value anyway.

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July 23, 2014

Optimization Intermediate Results

by Oleg Dzhimiev

Description

    Running OSLO’s optimization has shown that having a single operand defined is probably not enough. During the optimization run the program computes the derivative matrix for the operands and solves the least squares normal equations. The iterations are repeated with various values of the damping factor in order to determine the optimal value of the damping factor.     So, extra operands were added to split the initial error function – each new operand’s value is a contribution to the spot size (blurring) calculated for each color, aberration and certain image heights. See Fig.1 for formulas.
Fig.1 Extra Operands

Fig.1 Extra Operands

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July 1, 2014

Defining Error Function for Optical Design optimization (in OSLO)

by Oleg Dzhimiev

Description

The Error Function calculates the 4th root of the average of the 4th power spot sizes over several angles of the field of view.
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June 30, 2014

Open Hardware Lens for Eyesis4π camera

by Oleg Dzhimiev

initial_design_snapshot_2

 

Elphel has embarked on a new project, somewhat different from our main field of designing digital cameras, but closely related to the camera applications and aimed to further improve image quality of Eyesis4π camera. Eyesis4π is a high resolution full-sphere panoramic and stereophotogrammetric camera. It is a tiled multi-sensor system with a single sensor’s format of 1/2.5″. The specific requirement of such system is uniform angular resolution, since there is no center in a panoramic image. (more…)
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June 20, 2014

DDR3 Memory Interface on Xilinx Zynq SOC – Free Software Compatible

by Andrey Filippov

External memory controller is an important part of many FPGA-centered designs, it is true for Elphel cameras too. When I was working on the board design for NC393 I tried to verify inteface pinout using the code output from the MIG (Memory Interface Generator) module. I was planning to use MIG code as a reference design and customize it for application in the camera, adding more functionality to our previous designs. Memory interface is a rather intimate part of the design where FPGA approach can shine it all its glory – advance knowledge of the types of needed memory transactions (in contrast with the general CPU system memory) helps to increase performance by planning bank and address sequences, crafting memory mapping to utilize close to 100% of the bus bandwidth.
eddr3_bdiag

Fig. 1. DDR3 memory controller block diagram, source code at https://github.com/Elphel/eddr3

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March 31, 2014

Elphel, inc. on trip to Geneva, Switzerland.

by Alexandre Poltorak

University of Geneva

Monday, April 14, 2014 – 18:15 at Uni-Mail, room MR070, University of Geneva. Elphel, Inc. is giving a conference entitled “High Performance Open Hardware for Scientific Applications”. Following the conference, you will be invited to attend a round-table discussion to debate the subject with people from Elphel and Javier Serrano from CERN. Javier studied Physics and Electronics Engineering. He is the head of the Hardware and Timing section in CERN’s Beams Control group, and the founder of the Open Hardware Repository. Javier has co-authored the CERN Open Hardware Licence. He and his colleagues have also recently started contributing improvements to KiCad, a free software tool for the design of Printed Circuit Boards Elphel Inc. is invited by their partner specialized in stereophotogrammetry applications – the Swiss company Foxel SA, from April 14-21 in Geneva, Switzerland. You can enjoy a virtual tour of the Geneva University by clicking on the links herein below: (make sure to use the latest version of Firefox or Chromium to view the demos) Foxel’s team would be delighted to have all of Elphel’s clients and followers to participate in the conference. A chat can also be organized in the next few days. Please contact us at Foxel SA. If you do not have the opportunity to visit us in Geneva, the conference will be streamed live and the recording will be available.
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December 17, 2013

NC393 development progress – the initial software

by Andrey Filippov

The software used in the previous Elphel cameras was based on the GNU/Linux distribution supported By Axis Communications for their ETRAX processors. Of course it was heavily modified, we developed new code and ported many applications to run in the camera. Over the years we worked on making it easier to install, use and update, provided customized Live GNU/Linux distributions so those with zero experience with this operating system can still use the camera development software. Originally we used Knoppix-based CD, then DVD, then switched to Kubuntu when it became available and stable. And DVDs were eventually replaced by the USB flash drives. (more…)
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November 7, 2013

Elphel next camera – sample configuration

by Andrey Filippov

With all three of the new boards for the NC393 series cameras assembled (but only partially tested) it is now possible to connect them with the existent components and show some possible configurations. Main applications of Elphel cameras are scientific research, system prototyping, proofs of concepts designs – areas that routinely require unique configurations, and this new camera series will continue tradition of high modularity. The camera boards look nothing like Lego blocks, but nevertheless they can zip together in different ways allowing to make new systems with minimal additional hardware. Elphel new design values our prior work (hardware development is still expensive) and provides compatibility with the existent modules, simultaneously enabling new features that were not previously possible, The most obvious example – sensor interface. The 10393 board is designed to accommodate our existent sensor front ends, custom flex cables of different lengths and shapes. That will help us to reduce the transition period to the new camera so we can focus on the high performance system board and port portions of the software and FPGA code, code that is already proven to work. The same camera sensor ports will allow us to use multi-lane serial sensor connections needed for the modern high speed and high resolution devices, but we will work on this only after the first part will be done and we will be able to replace our current systems with the new ones. Implementation of the serial sensor connection has some challenges for us because the used protocols are not open and we have to rely only on the pieces of the available information and some reverse-engineering and research. It is not the most fun work to do, but being an Open Hardware/ Free Software company we will not provide our users with semi-open documentation. Our users will always be able to rebuild all the binaries from the source code – same binaries from the same code we have access ourselves. The only NDA Elphel ever signed was with Kodak – that sensor NDA had clear expiration time, so at the moment we planned to start distributing our products (and so the source documentation) we were not be bound by it anymore. Sample configuration illustrated below combines the new and existent modules, the later have links to the design documentation on Elphel wiki. It is not so for the new boards (10393, 10385, 10389) – no circuit diagrams, parts lists or PCB layouts are publicly available when this post is being written. Hardware errors are usually much more expensive to fix, and we do not want somebody to duplicate our hardware “bugs” until we consider our products (“binaries”) to be good enough to go to our users. So while we set up public Git repository when we start software development, we publish our hardware documentation simultaneously with the start of the product distribution – together with “binaries”, not ahead of them.
Sample configuration of the electronic modules of Elphel next camera family

Sample configuration of the electronic modules of Elphel NC393 camera family

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November 2, 2013

NC393 development progress – testing the hardware

by Andrey Filippov

10393 board, memory side

10393 board, memory side

We received the first prototype of the 10393 rev.’0″ – the new camera system board with all the BGA chips mounted. It took a little longer as our PCB assembly manufacturer had to order solder paste stencils as some chips (DC-DC converter module in LGA package and QFN chips with central thermal pads) required more than just applying tacky flux and running them through the reflow oven. The photo shows the 10393 system board together with the 10385 power supply board that I assembled earlier while waiting for the main one. This time the power supply is a separate module so we’ll not need different system board versions for different power supply options as we do with Elphel current NC353. (more…)
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October 29, 2013

Quadrotor copter with machine vision for contest

by Ivan Makarov

This page gives brief overview of multirotor UAV platform called “Tau”, which is built specially for participating in flying robots contest which is established by russian Croc company. For now contest has only russian participants, probably because it was made for a first time. 4 Our team name was “Autonomous aerospace”. We are from Krasnoyarsk, 1M people city in Siberia. We had experience in UAV airplane development and manufacturing. We’ve grew up from student and postgraduate student university (SFU) scientific team to startup company. (more…)
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