Search found 38 matches

by tcrass
2016-08-10T22:46:22-07:00
Forum: Users
Topic: Min and max values of LAB channels
Replies: 6
Views: 5663

Re: Min and max values of LAB channels

Hi there, and thank you so much for all your advice! The trick was -- apart from correct channel naming -- the "dot channel" notation like in "maxima.r". I had tried it the other way round ("r.maxima", thinking "the red channel's maxima"), but it obviously didn't work. IM uses -channel A for alpha. ...
by tcrass
2016-08-10T13:13:27-07:00
Forum: Users
Topic: Min and max values of LAB channels
Replies: 6
Views: 5663

Min and max values of LAB channels

Hi there, I've got a bunch of sRGB images with 16 bit color depth, and I'd like to now the minimum and maximum pixel values (in percent) of each channel after converting the image to LAB -- preferably as a one-liner per channel. I was tinkering a bit with identify -format '%[fx:minima*100],%[fx:maxi...
by tcrass
2016-05-27T08:13:34-07:00
Forum: Bugs
Topic: Large image processing problems..
Replies: 5
Views: 20218

Re: Large image processing problems..

Hi there, hi, magick would you please tell me which article described the algorithm of adaptive sharpen used in ImageMagicK. I second! Any information available about the implemented algorithm? (I tried to have a look at the source code, but for someone not deeply involved in ImageMagick memory mana...
by tcrass
2016-03-02T00:43:58-07:00
Forum: Users
Topic: 48 bit tiff: no-op convert results in pixel noise
Replies: 11
Views: 11580

Re: 48 bit tiff: no-op convert results in pixel noise

Hi, usually I avoid bypassing the distribution's package management system when installing software, but I gave libtiff (4.0.6-1) from the current Debian Testing release a try -- and it worked! No more pixel noise! So in the case of ImageMagick the verdict is "not guilty" ;) I'll file a bug report w...
by tcrass
2016-03-01T13:08:38-07:00
Forum: Users
Topic: 48 bit tiff: no-op convert results in pixel noise
Replies: 11
Views: 11580

Re: 48 bit tiff: no-op convert results in pixel noise

Fred,
fmw42 wrote:I will download the current example later today and check it out.
great! Thank you so much!

Cheers --

-- Torsten
by tcrass
2016-03-01T12:07:25-07:00
Forum: Users
Topic: 48 bit tiff: no-op convert results in pixel noise
Replies: 11
Views: 11580

Re: 48 bit tiff: no-op convert results in pixel noise

Fred, When I do convert -list format, I get TIFF* TIFF rw+ Tagged Image File Format ( LIBTIFF, Version 4.0.6 ) I am surprised that you do not get something like this. sorry, my fault -- I grep ped the output of convert -list format for 'tif', but without the -i option, so I missed the all-capitals T...
by tcrass
2016-03-01T08:23:40-07:00
Forum: Users
Topic: 48 bit tiff: no-op convert results in pixel noise
Replies: 11
Views: 11580

Re: 48 bit tiff: no-op convert results in pixel noise

Hi,

it seems neither
fmw42 wrote: What is your version of libtiff?

You can see versions from

Code: Select all

convert -list format
nor
fmw42 wrote:

Code: Select all

tiffinfo
would tell me which version of libtiff is installed, but according to Debian package management info I have libtiff 4.0.3-12.3.

Cheers --

-- Torsten
by tcrass
2016-03-01T01:45:56-07:00
Forum: Users
Topic: 48 bit tiff: no-op convert results in pixel noise
Replies: 11
Views: 11580

Re: 48 bit tiff: no-op convert results in pixel noise

Fred,

I was reluctant to post any of those tiffs 'cause they're really huge (not less than 150 MB), but anyway... I uploaded one to http://www.tcrass.de/files/tmp/01.tif.

Regarding the libtiff version, I haven't checked yet; I'll do as soon as I get home.

Cheers --

-- Torsten
by tcrass
2016-02-29T13:59:03-07:00
Forum: Users
Topic: 48 bit tiff: no-op convert results in pixel noise
Replies: 11
Views: 11580

48 bit tiff: no-op convert results in pixel noise

Hi there, once again I'm not sure if I'm just too stupid to use ImageMagick or if it's a real bug... So here's the story: I have some 48 bit TIFF files. When just loading and saving them using convert like in convert in.tif out.tif the resulting out.tif looks like mere pixel noise, with the outlines...
by tcrass
2014-08-01T14:19:28-07:00
Forum: Digital Image Processing
Topic: Surface of human vision "gamut"?
Replies: 12
Views: 16895

Re: Surface of human vision "gamut"?

Snibgo, He seems to confirm a thought of mine: in sRGB space, your colours are the ones on the surface of the cube, ie all the colours where any channel is 0.0 or 1.0. Convert all these colours to L*a*b* or whatever you want, and you have your answer. But don't quote me on this. It's just an idea, a...
by tcrass
2014-08-01T12:01:32-07:00
Forum: Digital Image Processing
Topic: Surface of human vision "gamut"?
Replies: 12
Views: 16895

Re: Surface of human vision "gamut"?

Hi everyone, just wanted to let you know that I finally got a kind and exhaustive reply from Bruce, and he gave me permission to quote him, too! So here's how he did the calculations for the color solid shown at http://www.brucelindbloom.com/index.html?LabGamutDisplay.html : 3D gamut extent surfaces...
by tcrass
2014-07-26T11:17:30-07:00
Forum: Digital Image Processing
Topic: Surface of human vision "gamut"?
Replies: 12
Views: 16895

Re: Surface of human vision "gamut"?

Snibgo, I know too little about how human colour vision is measured, but perhaps you are looking for "MacAdam limits". See the animation half way down http://en.wikipedia.org/wiki/Gamut . A search on this phrase turns up http://rua.ua.es/dspace/bitstream/10045/938/1/JOSA_A_24_6_1501_1515.pdf , an ac...
by tcrass
2014-07-26T07:39:53-07:00
Forum: Digital Image Processing
Topic: Surface of human vision "gamut"?
Replies: 12
Views: 16895

Re: Surface of human vision "gamut"?

Snibgo, Try the CVRL database: http://cvrl.ioo.ucl.ac.uk/index.htm thanks for the link, seems to be a rich resource of experimental data. However, nothing there that would help constructing the human vision "gamut" (maybe one should rather call it the "human vision device profile"?). Or maybe I'm ju...
by tcrass
2014-07-18T11:39:05-07:00
Forum: Digital Image Processing
Topic: Surface of human vision "gamut"?
Replies: 12
Views: 16895

Re: Surface of human vision "gamut"?

Fred, I have no ideas to help much. I would hope that there would be some medical data on that. yeah, I guess I could work myself through the original 1930s publications... However, I would prefer if I didn't have to. (Well, I've already found some Excel files obviously containing something like the...