16bits, 32bits, washed out colors...

[papaf]

Hi all,
a friend of mine is experiencing a problem since he switched from DSLR to ccd. He's now using a qhy8.
Being a little computer challenged, and not very keen on learning new softwares, he's still using what worked for his old DSLR: DeepSkyStacker to combine the shots and photoshop to adjust levels, curves, saturation and the likes.
This has somewhat worked even for the first few objects with the qhy8, but lately it stopped working. Granted, the object selection has increasingly been moving towards harder/more challenging ones, so I think this is what caused the problem.
Anyway, the fact is that, while DSS is happily throwing out results which seems ok, when the image is then taken in ps for final adjustments, it is very washed out, to the point that, after stretching, the starfield has no color at all.

Is it possible that saving the final DSS stack in 16bit formats is causing this? He obvioulsy has to do it because ps will only work in 16bit mode. Would using a 32bit format better this situation? And more in general: why is it better working in 32 bits when all the cameras seems to be 16bit anyway?

Thanks!

[Carlos Milovic]

Why do we have to work with bit depths beyond 8, even when we cannot see that quantity of color, and the monitors are not capable of displaying them anyway? When you are working a image, you want the maximum accuracy (without wasting space) you can, to avoid rounding errors. Every time you apply a process to a image, the pixel values are changed, rounded off, and some levels, if you have not the required bit depth, are merged. The later is known as posterization (btw. see the thread describing the HDRCombination tool, Juan posted an excellent example why 16 bits are not enough to store the data of that M42). Also, this is responsible for such things as gasps and voids in the histogram (so common on the PS world... but I have not worried about them in PI in years).

PS: PS works at 15bits, not 16.

[papaf]

Thanks Carlos for the very clear explanation. I stumbled on the HDR tool topic after I wrote here, and I've seen what you're talking about.
I even went further and tried both a 16bits and a 32bits save from DSS into PixInsight. The difference were subtle, but they were there.

Fabio

[Nocturnal]

Hi Papaf,

I think this qhy8 owner should learn how to use a computer and join us on the DSS/QHYCCD Y! groups to discuss his issues. 32b float to 16b integer conversion will not meaninfully influence color.  It will affect fine details but that's not what we're talking about here so let's not confuse the situation. He needs to learn to properly stretch and saturate his images. Ask for help with the PS crowd if he doesn't want to use PI

It's neither the fault of the QHY8 nor DSS You can point him at my site for examples of what that combination is capable of.