How do I paint accurate grey levels between 0-254 in an alpha or a greyscale image? Seems impossible ... Works in 5.5 .. not in CC. Bug?

Question

So here's the thing . I need to be able to assign accurate shades of grey in an alpha channel as our code takes the value (between 0-244) and uses it to do its thing. I assumed this would be easy .. just choose your colour and paint .. but not so.
In an alpha channel, or even in a greyscale image, make a selection and fill it with  RGB 6,6,6.  Since there doesn't seem to be a way to get a greyscale pallette or input the value for Alpha this is th eonly way I can see to do it.
Now, using the info panel, check that it is indeed RGB 6,6,6.  It is.
Now, make another selection and fill it with RGB 7,7,7.  Check this with the info panel and ...  its 6,6,6.
OK so now use levels or brightness to try to shift that 6,6,6 upto 7,7,7 ... check it with the eyedropper color sampler tool .
What you'll find is that the RGB value will go from 6,6,6 .. to  8,8,8  to 10,10,10     it's impossible to make it 7,7,7 or 9,9,9. Theres a whole bunch of other values that are also impossible.
If you do the above in any of the RGB channels themselves it will work fine .. its just the Alpha and in a greyscale image.
On a similar vein, on a regular layer, fill an area with you RGB 7,7,7, copy it and paste it into your alpha.  Looks fine .. until you use levels to increase the contrast and you'll find that what was 7,7,7 is now a noise filled mixture of, I assume, 6,6,6 and 8,8,8.
( NB. As a note the above also happened in CS5 but in an old version of Photoshop 5.5 it works perfectly .. I can give the RGB 7,7,7 and the value thats painted is 7,7,7. Bring it into CC and its fine. So its just the creation of tones in CC that is wrong.
Also, it works fine if you edit the individual RGB channels .. you can get 6,6,6 AND 7,7,7 .. but as soon as you copy and paste it into the alpha . .the 7,7,7 reverts to 6,6,6 )
So
Q1 .. what am I doing wrong?
Q2 .. if 8bit alphas and greyscale images can have values ranging from 0-254 .. then how do I define the value I actually want?  I can't use the K value as that's only a percentage so has fewer increments and there isn't a separate input for alpha value.
Q3 .. or put it more simply .. how do I set the grey value to a particular number, eg. 7
Thanks.
Pat
Message was edited by: Patrick Ward

Answer 1

Thanks Herbert. I'll have a good look at Photoline.
I don't know if these have anything to do with it but
the first is the color settings from CS5,
the second is the default from a demo install of CC14. I see the gamma tickbox but it doesn't refer to the alpha.
the thrid are the colour settings of PS 5.5. Note this is the one that gives the correct ( with respect to my expectations ) result