Does anyone know any good free program to reduce noise in images. My camera was set on ISO auto when i took some pictures and it made some of them at ISO 1000 - 1600.
Noiseware Community Edition is free of charge and does what you want.
I'd like to share an online tool for that.
The tool is hardly for professional use, rather for quick denoising before posting on facebook, etc.
I use Wavelet denoise GIMP plugin. It is very flexible and allows to control which noise and to what degree to remove (luma noise/chroma noise, how much of the details to preserve).
As usual, the more noise you remove, the less detail is left. However, if you want to remove only color noise (chroma noise), you can achieve a lot by working in YCbCr colorspace and processing only Cb and Cr channels.
Using the same image as John T. Original:
Enhanced (removed only chroma noise, nothing else, look under the tire and on the front glass):
Denoised with Wavelet denoise in YCbCr colorspace. Denoising params: Y: 0/1.0 (no chroma denoise), Cb: 7590/1.0, Cr: 7409/1.0. No undithering, no sharpening. You may note that color noise is removed but luma noise and details (!) remain untouched.
However, as the original image is badly dithered (ex-gif?), this may be helped too (dithering is not noise per se, but looks similar). Now I applied GREYCstoration filter with default parameters to smooth out dithering and sharpened the image with Refocus plugin to recover some lost details. You may also recover some sharpness by applying Unsharp Mask or better Smart Sharpen Redux.
Enhanced more (also smoothed dithered areas and Refocused):
All these GIMP plugins are free and cross-platform and work on Windows too. They give a great degree of control over what you obtain.