-> Red color and JPG???
in [Digital Cameras]
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From: Steve JORDI on 26 Mar 2010 08:36 Wow, thanks all for your explanations! At least there is a reason. And thanks too for the 1x1 tip... I actually never paid attention to those options and will work with them now! Sincerely, Steve JORDI M.Sc. in Geophysics (Remove the I_REALLY_HATE_SPAMMERS from my email address) ------------------------------------------------ 1197 Prangins Email: stevejordiI_REALLY_HATE_SPAMMERS(a)hotmail.com Switzerland WWW: www.sjordi.com ------------------------------------------------ Volcanoes at www.sjordi.com/volcanoes ------------------------------------------------
From: John Passaneau on 26 Mar 2010 09:32 On 3/26/2010 2:56 AM, Steve JORDI wrote: > Hi, > I tried to find an explanation on the web but without success. > > Does anybody know why the red color looks so ugly when a digital > picture is saved as JPG? > It looks like it's the only dominant color that gets very pixelated > and grainy. > The cause of this artefact? > > Thanks for any clue. > > Sincerely, > Steve JORDI > M.Sc. in Geophysics > > (Remove the I_REALLY_HATE_SPAMMERS from my email address) > ------------------------------------------------ > 1197 Prangins Email: stevejordiI_REALLY_HATE_SPAMMERS(a)hotmail.com > Switzerland WWW: www.sjordi.com > ------------------------------------------------ > Volcanoes at www.sjordi.com/volcanoes > ------------------------------------------------ You didn't say how the jpg was being generated, but as how a jpg looks is completely controlled by the software that generated it here are my suggestions of things to try.: Save it as something else like a tif which is not compressed. Find a different software package to do the compression, everyone has different ideas of how to do the compression. There is no standard on how to do the compression, just on how the output file is organized. Use less compression. Larger jpg's have less compression, the more a file is compressed the worse they look. I do jpg's only for web/electronics device use as I find the artifacts generated by the compression process unpleasant looking. If you are using a camera that only makes jpg's the only thing you could try is to make as large of jpg's as possible or get a different camera. John Passaneau
From: Better Info on 26 Mar 2010 11:05 On Fri, 26 Mar 2010 10:35:45 +0000, Martin Brown <|||newspam|||@nezumi.demon.co.uk> wrote: >Steve JORDI wrote: >> Hi, >> I tried to find an explanation on the web but without success. >> >> Does anybody know why the red color looks so ugly when a digital >> picture is saved as JPG? > >Mainly because your eye is strongly tuned to detecting ripe red fruit so >red always stands out much more. The same was noticable on slide films. >The same artefacts happen to saturated blue colours but they are much >rarer in nature. Although not at concerts under coloured spotlights. > >Flesh tones are another highly tuned sensitivity. Poor colour indicates >sickness and is best avoided. US NTSC TV newscasters used to drift >between green and purple but now are clamped to unreal pale orange. > >> It looks like it's the only dominant color that gets very pixelated >> and grainy. >> The cause of this artefact? > >The encoding to YCrCb and then subsampling of the chroma which by >default in JPEG is 2x2, most cameras do 2x1 and you can do 1x1. >Photoshop switches to 1x1 chroma sampling at level 6 in the current >version. Other packages offer an option to switch chroma sampling. > >It exploits the limited colour resolution in the eye to save space. >> >> Thanks for any clue. > >It isn't really a fault of JPEG so much as a feature of the chroma >subsampling trick used to get some extra compression. Your eye isn't all >that sensitive to colour detail compared to luminance so binning the >chroma 2x2 generally works well and saves a lot of bandwidth. It was >first used on colour TV transmissions. > >A demo of the JPEG Chroma subsamping artefacts using red and blue comb >patterns is on my webpage. It is based on pixel level detail in pure red >and blue which is an extreme test case for JPEG reconstruction. > >http://www.nezumi.demon.co.uk/photo/jpeg/combtest.htm > >A second demo of the generational losses with JPEG using 2x2 chroma >subsampling and 1x1 chroma is at: > >http://www.nezumi.demon.co.uk/photo/jpeg/2/jpeg2.htm > >If you posted an example of the problem you have encountered it might be >possible to help. There are known issues with commercial JPEG decoders >and monochromatic red and blue images. If that is your problem you are >best off decoding it as pretend monochrome luminance only data. > >Regards, >Martin Brown It's not just a matter of JPG sub-sampling. Many camera makers tweak the out-of-the-camera's JPG image so it's more eye-catching to the consumer who have had their color perception blown-out and overwhelmed with over-processed images in advertising for a century. Increasing contrast (losing dynamic range) and often oversaturating the red-channel (and others) to do so. If you use any camera with a full RGB histogram display available on it you can see this happening in real-time in the EVF or LCD display graph. The red channel is usually the first to get blown out on most any subject. When using a real-time RGB histogram (or RGB Zebra mode) on your camera it then becomes easy to set the camera's custom-color options so it more closely matches what it should be in the JPG output. I usually set contrast to -2 and only the red channel to -2. But that depends on the camera manufacturer as well. Then too, many camera makers just don't do a very good RAW to JPG conversion in the camera. This then forces the consumer to depend on and waste their valuable time on RAW and having to buy further software to repair what their camera failed to do properly in the first place.
From: Allodoxaphobia on 26 Mar 2010 11:24 On Fri, 26 Mar 2010 10:35:45 +0000, Martin Brown wrote: > > A demo of the JPEG Chroma subsamping artefacts using red and blue comb > patterns is on my webpage. It is based on pixel level detail in pure red > and blue which is an extreme test case for JPEG reconstruction. > > http://www.nezumi.demon.co.uk/photo/jpeg/combtest.htm "extreme" is correct -- especially when viewing with high index eyeglasses. One needs to view it 'straight on'. 'Tis a phenomenon I've observed for years when viewing LCD panels and those flat screen info displays at airports. Jonesy -- Marvin L Jones | jonz | W3DHJ | linux 38.24N 104.55W | @ config.com | Jonesy | OS/2 * Killfiling google & XXXXbanter.com: jonz.net/ng.htm
From: Robert Coe on 27 Mar 2010 10:07
On 26 Mar 2010 09:58:24 GMT, Chris Malcolm <cam(a)holyrood.ed.ac.uk> wrote: : Steve JORDI <stevejordiI_REALLY_HATE_SPAMMERS(a)hotmail.com> wrote: : > Hi, : > I tried to find an explanation on the web but without success. : : > Does anybody know why the red color looks so ugly when a digital : > picture is saved as JPG? : > It looks like it's the only dominant color that gets very pixelated : > and grainy. : > The cause of this artefact? : : Because bright red pigments are more easily come by than other : colours, and evolution has tuned plant fruits and flowers and animal : eyes to prefer it and to be most sensitive to small difference in red : quality. ... Actually, there are some plant flowers whose dominant color is ultraviolet; and bees, which care more about finding and differentiating flowers than humans do, have learned to see it. Bob |