Could This be Noise

: I have taken some shots today in Raw with Pentax K100D, The results are good apart from some like pixel blue on the edges off the foliage at the bottom. I am using Adobe Photo shop and nothing seems to remove it.
Whoever when they are converted to Jpegs this disappears,
Could this be noise I'm a bit of A novice with digital any help would be appreciated.
Kevin.

What ISO setting was it taken on? You only usually see noise at high ISO values, <800 (in my experience), and most of that is easily removed by the RAW converter. Noise also tends to appear not as a single colour but as patches and is more visible where you have areas of solid (and usually dark) colours. If it is a light blue fringe arouind objects at the edge of the frame it might be cromatic abberation produced by the lens. What lens are you using? Cheap lenses are more prone to that problem. It would help if you could post an example of the problem.

Look at the water in this image, the "graining" is due to having been shot at ISO800 late on a november afternoon

If you mean a very blue single dot (or very green) then this is probably a "stuck" pixel. You should find they always appear in exactly the same place on each image.

The RAW convertor should detect these and remove them, but in the preview you'll probably still see them. (I have quite a few on my ageing *ist-D and more when I use higher ISO settings).

Matt

Hi Tim
And thanks for your reply, The lens is SMC Pentax.DA 1:3.5-5.6 18-55 AL
Details 1/45s at f/13
ISO 200
Focal length 43mm
As for uploading photo I do not know how this is done. I guess that the shot has to be on A web server, That would probably mean that it would all so have to be A J.peg and as i have said once the shot is converted the problem is gone?
Many thanks Kevin

Kevin,
I've sent you a PM (private message) - I'll check out your RAW file if you want and let you know what's happening
Matt

Kevin,

If Matt can't sort your problem nobody can!

At ISO200 it's very unlikely to be noise, unless you have a very long exposure - i.e. measured in seconds. I haven't found the 18-55 to be too bad for CA either, so sounds like the stuck pixel Matt suggests.

If you join http://www.ephotozine.com/ you can upload pictures and link to them in the forums.

any possibility it's CA?

LOL @ Tim (Flattery will get you everywhere )

Don - I've been looking at the RAW file. It's not hot/stuck pixels. Kevin had accidentally pushed the exposure by 2 stops which had created an overexposed image, and the blue (from the water) seems to be "bleeding" through onto the foliage because of its luminance. There's perhaps a touch of CA in the image, but nothing really glaring.
Just confirming though...

FWIW, it's always worth checking your histogram to make sure the graph tails off before it hits the right hand side, especially when shooting RAW. You can always correct slight underexposure with RAW, but you can't do much for over-exposure! (And in general, the Pentax exposure system is excellent!)

Matt

Many thanks to you who posted on this tread, And A big thank you to Matt who sorted for me.
I will take A look at the link Tim.
Kevin.

Two points on that I think. For older photographers familiar with transparencies, in general if you expose as though you were making slides then you won't go far wrong. Overexposure is well understood to kill slides and the same is largely true of digital.

The second point is that the Pentax DSLRs if anything err towards under-exposure, which is a very good thing.

As regards histograms, it's worth adding (this is a third thing after all!) that you need to think what the histogram is representing. A nice even spread is not necessarily right. If you took a picture in a coal cellar you would expect a lot of black and the histogram would be, correctly, very much on the left...that is, if the exposure was correct....A picture of a white subject on a bed of snow would give a histogram very much to the right....and so on.

BTW, the actual problem was the "Shadow" warning on Adobe Camera RAW showing all the dark regions in blue

(Conversely, the "Highlight" warning will show in red.)

As Kevin said, problem sorted
Matt

P.S. John - I've edited your comment (you'd use the "Code" button by mistake!)

Theres a great plug in for photoshop users avilable free called de noise.
I use it for astro photo's and find it works really well on all images.
Its also worth looking at crispimage from the same company as I have found it the best and easiest to use sharpening tool available

http://www.softwhile.com/product_dn.html