Testing a Point Grey Camera for Fluorescence Microscopy

About two years ago, I mentioned Point Grey cameras. These are cameras sold to the machine vision and industrial inspection market, and are much cheaper than typical microscopy cameras – most are <$1000. Point Grey puts out very nice spec sheets listing all of their cameras, and the specifications for some are pretty impressive – cameras with < 3e- read noise for ~$500. Nico Stuurman has recently written a Micro-manager driver for these cameras, and was kind enough to let me test one of these cameras. We mounted it opposite a Hamamatsu Flash4.0 (an older Flash4.0, with ~72% QE), and did a qualitative comparison by taking sequential images of the same test slide on both cameras.

The Point Grey camera we tested was a Chameleon3 CM3-U3-31S4M. This uses a Sony IMX265 sensor, which has 2048 x 1536 3.45 μm pixels, with 71% QE, <3e- read noise, and sells for ~$500. It can run at up to 55 fps. On paper, this camera should perform almost as well as the Flash 4.0. The images below are of a Texas red-phalloidin stained cell, captured with a 20x / 0.75 NA objective and a 10 ms exposure on both cameras. Click on the images to see the full size image.

flash4-cy3-20x-10ms

The Flash 4.0 camera, 10 ms exposure. Click for full size.

ptgrey-cy3-20x-10ms

The Point Grey camera, 10 ms exposure. Click for full size.

A couple things are immediately apparent from these images. First, the Point Grey camera is clearly good enough to capture routine fluorescence images. Second, the smaller pixel size of the Point Grey camera actually gives better resolution images with the 20x / 0.75 objective. The resolution limit of a 0.75 NA objective at 600 nm is 0.61*λ/NA = 488 nm, so Nyquist sampling with a 20x objective would require 4.8 μm pixels; the 6.5 μm pixels of the Flash 4.0 undersample, and the 3.45 μm pixels oversample.

Second, the Point Grey camera is also somewhat noisier. In part, this is due to the fact that each pixel collects (6.5 μm / 3.45 μm)2 = 3.5-fold less light. To account for this we took a second exposure where we used a 3.5-fold longer exposure on the Point Grey camera.

The Point Grey camera, 35 ms exposure.

The Point Grey camera, 35 ms exposure. Click for full size.

With this longer exposure, and the same number of photons collected per pixel, the noise between the two cameras is much more comparable. The resolution improvement for the Point Grey camera is more striking using a 10x / 0.45 objective. Here, the 3.45 μm pixels pretty much exactly Nyquist sample, doubling the resolution achieved with the Point Grey camera compared to the Flash 4.0. Here, the exposures were chosen so that the number of photons per pixel should be constant.

Flash 4, 10x / 0.45 objective.

Flash 4, 10x / 0.45 objective.

Point Grey, 10x / 0.45 objective

Point Grey, 10x / 0.45 objective

Based on these simple tests, it seems clear to me that these cameras can be used at least for basic fluorescence microscopy. More testing will be needed to determine how well they will work for more demanding applications. There are already some issues that are apparent. First, it’s not clear if we had the camera optimally configured for these experiments. I think that we may have had the gain set too low, introducing quantization noise. Second, these cameras are not cooled, so dark current will be a concern for long exposures. Third, it is clear that there is insufficient hot pixel correction on these cameras. Compare these images with no light reaching the sensor.

Point Grey, 10 ms dark exposure.

Point Grey, 10 ms dark exposure.

Point Grey camera, 1s dark exposure.

Point Grey camera, 1s dark exposure.

Many of these hot pixels could probably be removed by a simple median filter following mapping of the hot pixels.

The IMX250 based sensors should perform even better – they are 5 megapixels, specified with 76% QE and 2.4 e- of read noise, and 3.45 μm pixels.

While more work is needed to make these cameras perform optimally, it’s also clear that they are already sufficient for many applications, particularly ones requiring high resolution with low magnification objectives. Furthermore, the very low cost of these cameras enables experiments requiring multiple cameras or low cost instrumentation where a conventional scientific camera would have been prohibitively expensive. I’m excited to see what people do with these.

 

9 thoughts on “Testing a Point Grey Camera for Fluorescence Microscopy

  1. I’ve used these cameras (particularly these newest Sony chips) in microscopy and they are great.

    Michael, Point Grey does their measurements according to the EMVA 1288 standard. Read noise is measured without electronic gain applied. Gain should not increase the read noise when expressed in electrons.

  2. Pingback: Austin's Imaging BlogPt Grey Camera Driver for MicroManager unleashes low-cost microscopy - Austin's Imaging Blog

  3. Hi there,
    I am working with a company that supplies Point Grey cameras. We have a number of customers that would be interested to read your blog. Do you mind if we share this link and your findings with them?

    Thanks:)

    • You are more than welcome to share the link. The whole site is licensed under a creative commons attribution-share alike license, so you can even reprint it and distribute it, provided you maintain the attribution to me.

  4. Please note, commercial interest here, but we thought it might be useful information based on this nice piece by Dr. Thorn.

    We have the following cooled cameras shipping now, using Sony CMOS chips similar to the IMX265/IMX250 sensors Dr. Thorn describes above.

    All cameras below are USB 3 (backwards compatible with USB 2), with two stage peltier cooling and Micro-Manager drivers (PC or Mac), available in mono or color.

    1) IMX174: Global shutter, 150+ FPS at 1936×1216 full frame, 5.86 um pixels, large FOV with almost 1″ sensor. This chip has sensitivity similar to the IMX250 mentioned above (more sensitive than the IMX265 tested), but with higher well depth, dynamic range, and frame rates. Our users have been very happy with this cooled camera for general fluorescence microscopy use, including low light applications.

    2) If you need smaller pixels so as not to be resolution limited with higher NA, low Mag lenses, we have another cooled model based on the IMX178 sensor, which has similar sensitivity to the IMX174 above, but with much smaller pixels (6.4 megapixel, 2.4 um pixels, 60 FPS at 3096×2080 full frame, medium FOV with ~ 0.6″ sensor).

    3) For high resolution brightfield work (or fluorescence in a pinch), we have an Ultra 4K HD model based on a DSLR sensor, with ~22 mm sensor diameter, sensitive 16.4 megapixel sensor, 3.8 um pixels, and better than 4K HD resolution (30 FPS at 4K HD resolution).

    We are also looking to bring the above-mentioned IMX250 chip (or similar) to our cooled platform, but in the meantime the IMX178 camera can substitute for low light fluorescence when smaller pixel size is critical (and the IMX174 has some advantages when 5.86 um pixels are OK).

    Please contact us if you are interested in any of these cameras.

    http://www.veroptics.com
    sales@veroptics.com

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