Episode 091: Growing Feathers

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BismarckThere was a question in the forum about how to desaturate and blur the surroundings of a figure. The blur and desaturation should follow the shape of the figure. I give an answer here – making a selection, storing it in a channel and then grow and feather it according to the needs of the task.

More information about selections, feathering. growing and shrinking them is in the outstanding GIMP documentation.

The image on the right is not made with this technique. I just tweaked the curve madly and used an insanely amount of unsharp mask.

Before all that I’ll take you to the work of Bert, who has combined images of the past and today. The results are stunning, have a look in this thread in the forum.

And at the end I’ll go back to the last show and finish the image that I made for selling a twin vacuum gauge. I left out the downscaling and sharpening. This gives the last kick for the image. The gauges are in the science collection of my school now – not on sale. ;-)

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13 thoughts on “Episode 091: Growing Feathers

  1. Ingenious! I might never have thought of using a feathered selection to achieve a gradient.

    Stick around here, and you can’t help but pick up new tricks! :)


  2. Rolf, supposing you were really serious about using the image of Bismark, how would you deal with the chromic aberration?

  3. Mathias – So what you are pointing to is that there is no simple and effective way to remove chromatic aberration using Gimp or any other open source software. However, Bibble, which works well in Ubuntu but is a commercial product, has a chromatic aberration removal process and I believe there might be some other Windows based pieces of software somewhere. I’ll do some research and report back.

  4. Would be wonderful! As far as I found out it’s much easier in the RAW before the de-mosaic steps. A new UFRaw version will have LensFun in it that does CA correction. If you can compile it on your own you’ll even have it already in the current version.
    Well, I won’t say it’s not possible in GIMP. It’s only difficult to get it looking nice. I am almost sure Bibble uses a similar algorithm that just desaturated the CAs.

  5. Mathias – I have LensFun installed and it does have a try at CA correction. Unfortunately, whilst it is possible to deal with the CA in UFRaw the correction does not carry over into Gimp.

    mramshaw – For effective CA removal you need to be able to magnify the image by at least 100% and the Gimp plug-in does not go beyond 50%. I am not sure what you mean by colour charts so it can’t be me. I found a rather interesting piece of software called PTLens but it is not free ($25) I think, although there is a free trial version and is for Windows but runs in Crossover. The only real drawback is that it seems to only work with JPEG files.

  6. @Norman

    I’m confused – which plug-in? The ufraw cropping/view plug-in is limited to 50%, I agree this is an issue.

    GREYCstoration, as far as I can tell, has no limit on zoom. How you ask for 100% though, I can’t tell.

    If this is not your experience, I’ll post one I built here for you … why is 100% so important for CA fixing?

  7. mramshaw – the plug-in is gimp-ufraw and, LensFun when installed, becomes part of UFRaw. LensFun has a zoom facility of its own but is not able to move about in the image therefore, it may not be possible to select the part of the image where the CA is present. Perhaps it is my eyesight but I find that I need to zoom in at about 100% to be sure I have removed as much of the fringing as possible. It is quite some time since I looked at GREYCstoration so I settle down and try it again.

  8. I now remember why I stopped looking into GREYStoration, I could not see how it could be used to remove the fringe efect of CA and I still can’t. Neither can I find any help files which might help an old thickhead like me to use the plug-in.

  9. @Norman – thanks for being my teacher today. Check ‘fixing CAs’ in the Future Episodes bit of the Forum.

    I’m sure it would probably be easy to add CA fixing to GREYCstoration, but it’s complicated enough as it is,
    so I’m much more happy having a simpler tool to use.

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Anything to add from your side of the computer?