Pixel Saturation

Sequence Generator
1

Hello,

When an image is captured a preview of it is shown in SGP. Is there a way to check for saturation in order to determine when an exposure limit is being reached?

Thanks

Farzad

2

@Farzad_k

Most cameras have 16-bit pixel wells which allows for a range between 0 and 65535. SGPro provides 3 ways to measure saturation:

  • Use the image stats module to look at “Max”.
  • Use the mouse to hover over bright areas. Below the image, you will see a field labeled “I” (intensity).
  • Use the histogram and look for “spikes” on the far right.

Keep in mind that, depending on manufacturer, a camera pixel can saturate before 65535 (I have seen several saturate at 64000).

3

Thanks. For the Max and Intensity, what number relates to saturation?
64,000 - 65,535?

4

Is this the “Max” that indicates over exposure?

image.png486×668 121 KB

5

@Farzad_k

Yep, that’s the one. Keep in mind that Max can also represent a hot pixel so you might want to use the mouse cursor inside a star or galaxy core (in the sampling area).

6

Okay, thanks.

The other issue is that apparently SGP Status values are for a16 bit
sensors, and the word on the streets has it that we have to manually
convert the numbers for the actual 12 or 14 bit rate of a DSLR-type sensor.
How true is that?

Additionally, if I set my RAW capture in-camera to either 12 bit or 14 bit,
would that affect the images that are captured through SGP? I imagine all
that SGP does is get the camera to capture RAW file, internally open the
RAW file and insert shooting header in the file, close it and name it .fit

  • is this a correct assumption?

It makes me winder why the actual sensor bit rate is not also included in
the header for software like PI to process accordingly. And maybe that
information is not critical?

Farzad

Farzad

7

It’s not true, no conversion is necessary (we have already done that).

For sure. We will up-convert all your FITS images to 16-bit (RAW is untouched), but changes the depth of a pixel well will always affect your image.

8

So you are saying that no matter what the sensor bit rate, SGP internally
converts the data to 16 bit values and so what we see is what there is.

9

All FITS data is 16-bit. Raw data is dictated by the camera, but image stats are displayed as though it were 16-bit.

10

Okay, I think I get that whatever the sensor bit-rate happens to be since
FITS is a 16 bit environment then SGP converts that data internally and
presents it in a 16 bit environment. And what we see is reliable then.

Thanks.

Farzad

11

Ken, reference your comment on hot pixels would it difficult to provide a count of the saturated pixels to allow these to be ignored when establishing exposoure times.

Thanks George.