Mirage Recorder

[John C. Butler]

A little on the expensive side, but this camera appears to have some real potential. With all those interesting add-ons you're developing I wonder what the final cost of such a product might be.

[Take Vos]

I just found out that Final Cut Pro does not handle 16 bit per component RGBA pixel values (QuickTime does). It seems I have to support r4fl, which is a Y'CbCrA pixel format with 32 bit floats for each component.

For the debayer decompressor this is not that bad, as most debayer algoritms like to use YUV/Y'CbCrA/CIE Lab anyway, so I don't have to convert it back to RGB anymore, so it is a win :-)

For the timeline compressor/decompressor I will probably store in a 16 bit float per component Y'CbCrA. OpenEXR also uses 16 bit floats, but in RGBA.

I did however get the timeline codec functionality working and can say that my plan is working, the camera footage does not need to be rendered anymore by Final Cut Pro.

The only issue I have is that FCP likes to open and close my codec for each frame rendered as you are scrubbing through the timeline. My open call takes a while, as it is setting up an OpenGL context. I hope I can fix this by keeping a set of initialised contexts available for re-use.

[Take Vos]

I've received my new lens a: Fujinon CF16HA-1, 16mm, f1/1.4

Here are two pictures showing off a shallow depth of field, 1 and 2 meters from the subject.

http://www.vosgames.nl/products/Mira.../new_lens1.png
http://www.vosgames.nl/products/Mira.../new_lens2.png

Don't mind the noise, I am experimenting with the debayer and calibration system.

[Take Vos]

Hi, I've just designed and ordered a gate that will fit in front of the sensor of the Pike. At least, I hope it will fit, I might have made it to thick to fit in the space between the sensor and lens.

The gate will cover part of the sensor so that the black part of the image can be used for continues calibration.

The gate will be around 870 pixels height, the camera will record 930 pixels height. The final picture will be 1920 x 800 pixels (2.40:1 ratio), so you have some wiggle room.

[Take Vos]

Hi,

I can now confirm that my codec will work in high quality. I implemented AHD in 32bit floating point and Final Cut Pro will use 32 bit floating point Y'CbCrA to render the image.

I tried using the Color Corrector 3-way filter and made some extreme modification.
During preview the video scopes/histogram shows that there are quite a few gaps (color banding), which is logical as the preview is rendered in 8-bit.
After rendering the histogram shows solid again and the image shows no effects of color banding.

[Take Vos]

I've been working on the recording application, specifically the preview screen.
The preview screen has three modes: color, focus and exposure.

- Color, simply the standard view most cameras have, it will be very honest and will show what the sensors sees, including sensor inbalance, dead pixels and fixed pattern noise, no white balance or other color corrections either.

- Focus, this is a simple edge detection algorithm, using only the green pixels. So the image is black except for the places where there are a lot of high frequency components. This should help with focusing, without requiring a large high definition screen.

- Exposure, this shows in false-color the amount of light falling on the sensor, so blue is dark, green is medium, red is bright, white is almost clipping. Because it shows the value of the maximum color component at that location it will allow for shooting colors that are brighter than maximum white.

The latency is pretty low. Because so little processing is going on the computer stays cool as well, which is kind to the sound mixer.

I also thought of a way to cool the camera without making noise, with PCs these days there are now very efficient cool blocks without a fan, together with a peltier element I probably can get at low temperatures (5 degrees Celsius). The camera will look very freaky though with such a contraption attached to it.

Here are some pictures for these cool blocks:

http://www.silentpcreview.com/article187-page1.html

http://www.frozencpu.com/products/63...11&id=3Mns9ctm

http://www.tweaknews.net/reviews/zer...ler/index3.php

http://www.thetechlounge.com/article...pe+CPU+Cooler/

[Daniel Lipats]

I was really looking into using one for my camera but I found them to be huge. So big that a lot of people had trouble fitting them onto the motherboard, and closing the pc case.

My next choice was water cooling. Not too big, defiantly quiet. But the water adds considerable weight to the camera, which I had designed to be shoulder mount.

In the end I decided to go with the Roswell Z2ex
http://www.newegg.com/Product/Produc...00025&Tpk=z2ex

Performs very good, and for a CPU fan its not loud. I use it on my Q6600. At the height of 71mm its still big. But fits very nicely into my design.

Interesting project by the way. Looking forward to more.

[Take Vos]

I have some success with black clamping.

I have received the gate (that I designed) that fits in front of the sensor to get a few black lines for continues calibration. I get some black lines, but because there is room between the gate and the sensor (because the sensor is covered by a piece of glass) the number of black lines become less as the iris is opened.

I now record 140 extra lines at the bottom of the frame, for a total of 1920 x 940 pixels. I have to use my lens with the iris set to f/2 or higher to keep 8 black lines at the bottom of the frame.

If I would average these 8 lines and then subtract them from all the other lines you get lots of strobing vertical lines, quite annoying. by also averaging these black lines for the last 8 frames I get a much smoother image. The image looks as smooth as the original, but much darker of course.

with enough luck this, together with the linearity algorithm will completely solve the balancing (the two halves of the sensor) problems.

Cheers,
Take

[Take Vos]

Because of the black clamping I can really see the actual noise of the sensor, it seems a lot of the noise if caused by electronic interference.
I especially noticed just now when wiggling the firewire 800 connector that the noise became more or less.

Luckily I ordered the fibre version of the Pike on purpose, I want to feed camera with its own stabilised power and use optics to separate the electronics. I will also design the electronic trigger system to be galvanic separated.

I also finally got the camera to smear, by pointing it at a halogen light source at high shutter speed and over exposed. The algorithm will compensate for the smear in around 8 frames or 1/3 of a second. So you will see the smear if you pan the camera, but if you lock the camera down the smear will not be noticeable.

[Take Vos]

As I said I now have color, focus and exposure modes on the viewfinder, here are some screenshots of it in action in Boom Recorder.

http://www.vosgames.nl/products/Mira...eenshots.shtml

I have also included a 1280 x 720 shoot and protect area, for people who like to shoot at a theatrical 1920 x 800 and at the same time a full screen 720p for on TV.

[Emre Safak]

What do you think of the gamut? The color looked less than stellar in your recent pictures.

[Take Vos]

Hi Emre,

I've decided to not compensate for anything except black level inside the recording application, so the colors are not white balanced and the color space is camera RGB.

Together with calibration data prepared by a calibration program, the codec will show much more correct colors, and should be at least as good as the older pictures.

Calibration can be done using the sun and: a white (how white doesn't even matter) sheet of paper and a gretag macbeth color target. The calibration program will then linearise the pixels from the white sheet of paper; and white balance and color matrix calculations from the gretag macbeth.

[Take Vos]

Here is a image that was exported from the QuickTime player. As the QuickTime player uses the low quality high speed playback the image has not been processed using calibration data and there are many artefacts from the "nearest neighbour"-demosaic algorithm.

http://www.vosgames.nl/images/Mirage...colorfield.png

I guess everyone will recognise the gretac macbeth color target, it has been lit by natural light through a cloud. I guess that corresponds to a D50 white point, please correct me if I am wrong because a lot of calculations will depend on this.

The image has been processed in 8 bit (from 14 bits linear from the sensor, through 12 bits non linear during data transfer), with a gamma of 1.8 (native Apple gamma)

[John Papadopoulos]

You should ideally get white noise with a very clean FFT transform. If you get diagonal lines that tend to move it is interference. If you get horizontal lines moving up and down at extreme gain, it's probably realistic limitations of electronics. An ideal camera would reproduce only white noise from the sensor. If you test this with fft, do it before debayering without any balance of colors.

[Take Vos]

Hi John,

They are horizontal blocks moving/flickering, but the amplitude is clearly changing when moving the firewire cable. Which looks to me as a low frequency interference. I think with its own power supply and not electrically connected to anything else will reduce the problem significantly.