Re: Fast from 16bit to gtk image buffer

[John Cupitt <john cupitt ng-london org uk>]

Hi,

Piotr Legiecki wrote:
> I'm writting simple program which will operate on 16bit per RGB channel 
> (tiff, scanned images) files. 
> ...
> So in summary:
> I want to manipulate 16 bit per channel image and display the changes as 
> fast as possible using gtk window (not sure if gdkpixbuf or GdkRGB).

Most TIFF files do not support random access (only tiled tiff, AFAIK), so I would:

- unpack the TIFF file to a large memory buffer, organised as RRGGBBRRGGBBRRGGBB etc.

- write something to process from this to an 8 bit RGBRGBRGB memory buffer, perhaps with subsampling and region of interest too ... include your curve adjust look up tables at this stage

- repaint the screen from the 8 bit memory buffer using gdkRGB

- you will need to look out for things like scrolling ... I'd do the conversion in the expose event of a GtkDrawingArea, then pack that into a scrolled window 

- you could use gdkpixbuf, but if you're doing subsampling and ROI stuff yourself, the convenience benefits of gdkpixbuf will be a bit marginal (I think)

I maintain an image processing library and GUI that does (roughly) this, you could take a look at the performance of that:

 http://www.vips.ecs.soton.ac.uk/

the gtk2 version is much less optimised, but the gtk1 one is pretty quick (IMO). Try loading a huge TIFF (Insert=>Image from file), double-click on the thumbnail to open a viewer, click on View=>Show display control bar, then drag the left-hand slider. Press '0' to zoom out to fit the image to the window. I get several frames per second update on a 4GB image.

John