GIMP Plugin Registry

The wavelet denoise plugin is a tool to selectively reduce noise in individual channels of an image with optional RGB<->YCbCr conversion. It has a user inteface to adjust the amount of denoising applied. The wavelet nature of the algorithm makes the processing quite fast.

Features

• User interface with preview is available.
• Amount of denoising for each channel is selectable.
• Possibility to denoise YCbCr channels instead of RGB exists.
• Conversion from RGB to YCbCr is lossless.
• Calculations are done on linear data (not gamma-corrected data).
• Preview is capable of displaying one single channel if desired.
• Processing time is reasonably fast (around 10 seconds for a 10 Megapixel image) and independent from the amount of denoising applied.

Details

The wavelet denoise plugin for The GIMP reduces noise in an image using the algorithm copied and slightly altered from the UFRaw program [Udi Fuchs] (which inherited the algorithm from dcraw [Dave Coffin]). Instead of denoising all RGB channels at once, the plugin implementation allows to denoise the RGB channels individually and - even more useful - to denoise the YCbCr channels individually. The YCbCr conversion is nearly lossless as the internal calculations are done in floating point numbers and rounding errors are avoided. Because the algorithm implements a wavelet filtering it runs quite fast.

Preview

This is part of a picture taken with the Nikon D80 DSLR camera at ISO 1600 in RAW format. The face is lit by two candles and a colour temperature setting of 2500 K was used. The file was opened with the UFRaw plugin.

The goal is not to reduce all noise. The unpleasant part is the chroma noise which appears only when shooting the camera in RAW mode at a high ISO speed. As you can see the colour (chroma) noise is almost completely gone in the second picture and the luminance noise is slightly reduced. Especially in the lower right corner of the preview image the improvement is apparent. If you look closely at the face you will notice that the image details have not been altered much, the sharpness is almost the same.

Note that this is just the result of a uniform application of the filter on the unprocessed image. Masking the filter effect with a selection is possible which could improve the result even more.

What's new in version 0.2

There are several changes that have been made to improve the plugin.

• The denoising is done on linear data now. The sRGB gamma of approximately 2.2 is compensated.
• The interface has been reorganized
• A 'Detail' slider has been added which affects the thresholds dependency on noise frequency.
• Tool-tips have been added.
• The single channel preview can now be displayed in colour.
• There is a 'Reset' button which resets the currently selected channel temporarily (during the time the button is pressed).
• Normal reset buttons have been added.
• The size of the dialog is saved now after it is closed.
• The default thresholds are all zero now.
• The progress bar was fixed and tweaked.

Apart from that minor other changes have been made.

License