Pixel value tool and FX Highlight Over Exposed

[Jean-Francois]

Hello Robin,

The tool "Pixel Value Readout" and the FX "Highlight Over Exposed" do not work properly together.

I think that when the FX "Highlight Over Exposed" is activated, the image data is downscaled to 8 bits.
So the Pixel Value Readout shows a value between 0 and 255. If the FX tool is deactivated, then the pixel value(s) change back to normal.

In addition ... can you change the colour of the highlight ... from black to red (at least for mono camera).
If you want to add something more ... then you can for example show the pixel below 0 (or exact 0) with a blue colour.

Regards,
Jean-Francois

[admin]

Hi,

a number of the 'FX' options only work on 8 bit images, which means that when you apply them to a 16 bit image the code automatically drops the image to 8 bit before processing. This is generally OK since the image by that point is only going to the screen which is 8 bit anyway. However the pixel value code plugs in just before the frame gets to the display, so picks up the modified values.

I will have to think to see if I can get the pixel values at an earlier stage, but that might have issues in other ways. Yuck...

cheers,

Robin

[Jean-Francois]

Hello Robin,

OK, I understand that some part are done in 8 bit other in 16 bit.

The FX tool shows where the image is overexposed ... the pixel value shows the ADU value of the pixel.
It is "surprising" that the value jumps if the FX tool is activated.

I have no need (now) for this. But the idea to colour in red the overexposed pixel (and blue the underexposed or 0 pixels) could be interesting.
I used the Shack-Hartmann software from the Optocraft company. It has this capability to show the under and overexposed pixels.

Note: that would save me a complete session of observation with my spectrometer yesterday evening.
For some reason, the QHY-183 camera does not open all the parameters at the start.
SharpCap was showing offset = 60 (as usual), but intern the camera was with an offset of zero.
The result was ... all my darks, offsets and light images have the histogram truncated.
The other strange behaviour ... I click on the "60" then Return ... nothing was changing.
SharpCap changed the offset only after typing a new number (and Return).

So the FX tool can be very useful to have a quick view of the overexposed and underexposed (or zero) pixels.

Regards,
Jean-Francois

[admin]

Hi,

yes, in most places you need to actually make a change for the value to get sent to the camera - SharpCap will look at the new value, decide it is the same as the existing one and that it needs to do nothing. You have to make this check at some point or you can end up in an infinite loop with the camera code sending a value of 60 to the camera and then sending out an update message to the UI that the value is now 60. The UI receives the message that the value is now 60 and if it didn't check for equality then it would send *another* message to the camera to set the value to 60 and round and round you go...

Changing the resolution, bit depth or something similar that causes the camera to stop and restart causes the values displayed to get refreshed from the camera - that shouldn't make a difference, since if SharpCap shows 60 it will have sent 60 to the camera, but if the camera ignored it then a refresh will (should) bring back the current value. That's of course providing that the QHY SDK hasn't remembered the 60 but didn't bother sending it to the camera - in that case everything *except* the camera thinks that 60 is the current value...

cheers,

Robin

[Kai Getrost]

Another vote to change the overexposed pixels in the Highlight Overexposed tool from black to red (at least for monochrome cameras). I was defocusing a bright star image with Highlight Overexposed, to spread the PSF out and reduce clipping. But it was hard to see the transition from "black pixels are mostly overexposed" to "black pixels are mostly nulls in the roiling interference rings" as I defocused. Red overexposed would help with that. Thanks.

-Kai

[donboy]

I don't know whether changing from black to red will affect 'Mask Over Exposed Pixels' which is in Black.

Don

[admin]

Hi Don,

mask overexposed is separate code, so wouldn't be affected by any change here.

It's not 100% simple, since currently the image is processed for overexposed in its native form (ie MONO or RAW if appropriate). To make a red highlight I would need to convert to RGB at that stage - not sure if it would have a significant performance impact, but I would have to check.

cheers,

Robin