So you have just taken delivery of a brand new PXW-FX9. Turned it on and plugged it in to a 4K TV or monitor – and shock horror there are little bright dots in the image – hot pixels.
First of all, don’t be alarmed, this is not unusual, in fact I’d actually be surprised if there weren’t any, especially if the camera has travelled in any airfreight.
Video sensors have millions of pixels and they are prone to disturbance from cosmic rays. It’s not unusual for some to become out of spec. So all modern cameras incorporate various methods of recalibrating or re-mapping those pesky problem pixels. On the Sony professional cameras this is called APR. Owners of the Sony F5, F55, Venice and FX9 will see a “Perform APR” message every couple of weeks as this is a function that needs to be performed regularly to ensure you don’t get any problems.
You should always run the APR function after flying with the camera, especially on routes over the poles as cosmic rays are greater in these areas. Also if you intend to shoot at high gain levels it is worth performing an APR run before the shoot.
If your camera doesn’t have a dedicated APR function, typically found in the maintenance section of the the camera menu system, then often the black balance function will have a very similar effect. On some Sony cameras repeatedly performing a black balance will active the APR function.
If there are a lot of problem pixels then it can take several runs of the APR routine to sort them all out. But don’t worry, it is normal and it is expected. All cameras suffer from it. Even if you have 1000 dead pixels that’s still only a teeny tiny fraction of the 19 million pixels on the sensor.
APR just takes 30 seconds or so to complete. It’s also good practice to black balance at the beginning of each day to help minimise fixed pattern noise and set the cameras black level correctly. Just remember to ensure there is a cap on the lens or camera body to exclude all outside light when you do it!
An F3 user was given access to the service manual to remove a stuck pixel on their F3. It was found in the service manual that you can address pixel manually to mask them. There are pixel positions 1 to 2468 Horizontally and 1 to 1398 vertically. This ties in nicely with the published specifications of the F3 at 3.45 Million Pixels.
At the LLB (Sound, Light and Vision) trade fair in Stockholm this week we had both a SRW9000PL and PMW-F3 side by side on the stand, both connected to matching monitors. After changing a couple of basic Picture Profile settings on the F3 (Cinegamma 1, Cinema Matrix) Just looking at the monitors it was impossible to tell which was which.
Over the next few posts I’m going to look at why sensor size is important. In most situations larger camera sensors will out perform small sensors. Now that is an over simplified statement as there are many things that effect sensor performance, including continuing improvements in the technologies used, but if you take two current day sensors of similar resolution and one is larger than the other, the larger one will usually outperform the smaller one. Not only will the sensors themselves perform differently but other factors come in to play such as lens design and resolution, diffraction limiting and depth of field, I’ll look at those in subsequent posts, for today I’m just going to look at the actual sensor itself.
Pixel size is everything. If you have two sensors with 1920×1080 pixels and one is a 1/3? sensor and the other is a 1/2? sensor then the pixels themselves on the larger 1/2? sensor will be bigger. Bigger pixels will almost always perform better than smaller pixels. Why? Think of a pixel as a bucket that captures photons of light. If you relate that to a bucket that captures water, consider what happens if you put two buckets out in the rain. A large bucket with a large opening will capture more rain than a small bucket.
Bigger pixels capture more light each.
It’s the same with the pixels on a CMOS or CCD sensor, the larger the pixel, the more light it will capture, so the more sensitive it will be. Taking that analogy a step further if the buckets are both of the same depth the large bucket will be able to hold more water before it overflows. It’s the same with pixels, a big pixel can store more charge of electrons before it overflows (photons of light get converted into electrical charge within the pixel). This increases the dynamic range of the sensor as a large pixel will be able to hold a bigger charge before overflowing than a small pixel.
All the electronics within a sensor generate electrical noise. In a sensor with big pixels which is capturing more photons of light per pixel than a smaller sensor, the ratio of light captured to electrical noise is better, so the noise is less visible in the final image, in addition the heat generated in a sensor will increase the amount of unwanted noise. A big sensor will dissipate any heat better than a small sensor, so once again the big sensor will normally have a further noise advantage.
So as you can see, in most cases a large sensor has several electronic advantages over a smaller one. In the next post I will look at some of the optical advantages.
Camera setup, reviews, tutorials and information for pro camcorder users from Alister Chapman.