Sharpcap histogram

[jambouk]

I'm helping someone out [i think] with setting up their SPC900 to do some planetary imaging.

With the histogram turned on, what does the X-axis represent? The values go from 0 to about 256.

Also, are there any advantages / disadvantages of selecting tthe SPC900 in the drop down list of cameras where it appears under the LX option - I don't mean ticking the "LX" box, but the camera appears twice in the list of cameras, once with "LX" after its name, but you can still use that option without doing long exposures. It is a bit confusing as the sliders change and the options of things to adjust is different depending which version of the SPC900 one picks.

I don't have the camera am just trying to help remotely (a few hundred miles away) which makes it even more difficult.

James

[rwg]

Hi James,

In the histogram the X axis represents pixel brightness and the Y axis the number of pixels with that brightness, that's pretty much standard for how the histogram works in imaging applications. Basically you don't wan't the graph to be above zero at the right hand end, because that would imply that you have saturated pixels and therefore things are too bright.

The LX mode option for the SPC900 in the cameras menu is there for those who have done the long exposure modification on their camera. WIth the mod, rather than the camera running it's own frames at 10, 20 or whatever frames per seconds, exposures are controlled by SharpCap via either the serial or parallel port. Unfortunately SharpCap has no way to tell if you've really got an LX modified camera or not, so it just goes along with whichever option you choose. If you don't have the LX modified camera then the LX option will sort of look like it's working, but it won't be quite right, so it's best to stick with the first SPC900 entry.

General rule of thumb in SharpCap is to pick the entry for your camera nearest the top of the menu as that will usually give you the best results.

cheers,

Robin

[jambouk]

Robin, that is really helpful, thank you. I suspected the X-axis was "brightness" but was confused that its range was 0-256 and also the colour range was up to 256 on a drop down box on the right.

Is it possible to see how much "compression" occurs to the data for various frame rates? I know the advice is generally the SPC900 should not be used over 10fps because the compression kicks in, but is it possible to compare how much compression happens at 1fps, 5fps, 10 fps?

James

[jambouk]

Can someone explain why the histogram of my Logitech 4000 Pro is much broader than that of the ASI120MC, and has a less symmetrical appearance? No IR cut filter on either in this test (and adding the IR cut filter doesn't alter things much); I adjusted gain, gamma, brightness, white balance etc and nothing changed the appearance of the two greatly. Both cameras pointing at the same light source (window) in this test and exposures adjusted to get about 50% along the X axis.

James