Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
09-15-2015, 02:38 PM   #1
Senior Member




Join Date: Jul 2015
Posts: 110
Digital cameras and red

Digital cameras seem to struggle with handling red accurately and on my K30 things like red flowers come out far too vibrant.

Is there a way round this? On other cameras I can alter RGB settings independently but the K30 they seem all merged together so you can make it more or less vibrant but not tone down a specific colour.

I guess it can be tweaked better in Raw, but wondered if there was a way of getting the camera to respond better in the first place?

09-15-2015, 02:55 PM   #2
Site Supporter
enoeske's Avatar

Join Date: Jul 2009
Location: Surprise, Az
Photos: Gallery
Posts: 1,920
QuoteOriginally posted by Oricman Quote
On other cameras I can alter RGB settings independently
Do have any examples of this? I've never seen that feature before.
09-15-2015, 04:48 PM   #3
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,264
QuoteOriginally posted by Oricman Quote
I guess it can be tweaked better in Raw, but wondered if there was a way of getting the camera to respond better in the first place?
A good working solution is to avoid overexposing your red flowers. You can set the immediate preview image to include histogram data and set the playback mode display to include channel specific histograms. This should allow you to visualize the red channel clipping. Set the exposure comp down until the clipping is no longer evident.

The knee jerk response is to say that this will cause a general underexposure except for the red flower. True enough, that may be the outcome, though the camera is not to blame for the spectral balance within the frame. The simple truth is that unless exposure is lower, the red channel will clip. If the results are not pleasing and cannot be fixed in post-processing, another option would be a merge of exposure bracketed images. The better HDR/merge tools allow tuning by color channel.


Steve
09-15-2015, 05:46 PM   #4
mee
Pentaxian




Join Date: May 2010
Posts: 5,868
detail in red seems to be a difficult choice for Pentax cameras.. There is a review on DPR (IIRC) that shows different cameras and their rendering of different colors. The more modern K-3 and K-3 II does a pretty decent job.. but the 'older' bodies seem to be a little off in capturing detail in red.

But if yours are just to loud (still with detail) just do what steve said.. underexpose a little.. you can cut down on vibrancy in post and/or bring up the darks. The key is retaining detail.. low ISO and only enough underexposure to retain the detail.

09-15-2015, 09:53 PM   #5
Pentaxian




Join Date: Nov 2013
Location: North Carolina
Posts: 1,095
QuoteOriginally posted by Oricman Quote
Digital cameras seem to struggle with handling red accurately and on my K30 things like red flowers come out far too vibrant.

Is there a way round this? On other cameras I can alter RGB settings independently but the K30 they seem all merged together so you can make it more or less vibrant but not tone down a specific colour.

I guess it can be tweaked better in Raw, but wondered if there was a way of getting the camera to respond better in the first place?
You can underexpose but you won't get the image you want. DSLR sensors get blown luminance values all the time. Capture a raw file and simply reduce luminance values and maybe a bit of saturation. Both of these were with K20's 5 years ago, not much has changed.



09-16-2015, 03:45 AM   #6
Senior Member




Join Date: Jul 2015
Posts: 110
Original Poster
Wow, Brooke. That's pretty impressive.

---------- Post added 09-16-15 at 03:47 AM ----------

QuoteOriginally posted by enoeske Quote
Do have any examples of this? I've never seen that feature before.
Hmmm, now I'mm looking at my old camera it doesn't seem to do that. Maybe I've got it wrong. I think one of my older cameras allowed tweaking of RGB but maybe not.
09-16-2015, 03:52 AM   #7
Senior Member




Join Date: Jul 2015
Posts: 110
Original Poster
This is the sort of thing image I get. The red can be so intense it bleaches out any detail. It's not a problem particular to Pentax - I've had reds pop out on most of my digital cameras.

---------- Post added 09-16-15 at 03:59 AM ----------

QuoteOriginally posted by stevebrot Quote
A good working solution is to avoid overexposing your red flowers. You can set the immediate preview image to include histogram data and set the playback mode display to include channel specific histograms. This should allow you to visualize the red channel clipping. Set the exposure comp down until the clipping is no longer evident.

The knee jerk response is to say that this will cause a general underexposure except for the red flower. True enough, that may be the outcome, though the camera is not to blame for the spectral balance within the frame. The simple truth is that unless exposure is lower, the red channel will clip. If the results are not pleasing and cannot be fixed in post-processing, another option would be a merge of exposure bracketed images. The better HDR/merge tools allow tuning by color channel.
Thanks Steve. I have the exposure up a little as I seemed to be getting some under-exposed images. I'll trying dialing it back a bit.
Attached Images
View Picture EXIF
PENTAX K-30  Photo 
09-16-2015, 04:42 AM   #8
rfg
Senior Member




Join Date: Dec 2010
Location: Sydney
Posts: 137
QuoteOriginally posted by mee Quote
detail in red seems to be a difficult choice for Pentax cameras.. There is a review on DPR (IIRC) that shows different cameras and their rendering of different colors. The more modern K-3 and K-3 II does a pretty decent job.. but the 'older' bodies seem to be a little off in capturing detail in red.
It's more that the Pentax jpeg engine has trouble with reds. If you look at Imaging Resource's famous fabric swatches most Pentax cameras lose all detail very quickly in the red swatch, ie iso 1600 and above, but if you download the raw image from the site the detail is there. The jpeg engine is applying a lot of colour noise reduction esp in the red channel.

09-16-2015, 06:36 AM   #9
Veteran Member




Join Date: Jul 2010
Location: Lyngby, Copenhagen
Photos: Albums
Posts: 742
See this old thread: https://www.pentaxforums.com/forums/6-pentax-dslr-discussion/298860-pentax-jp...ml#post3317018
where Giklab came up with using the Muted setting for handling "problem" reds in camera.
Regards,
--Anders.
09-16-2015, 06:52 AM   #10
Site Supporter
enoeske's Avatar

Join Date: Jul 2009
Location: Surprise, Az
Photos: Gallery
Posts: 1,920
This is probably my favorite example of "red" from my collection. As others have mentioned, the key is to keep an eye on the RGB histogram and not clip the red channel. You can edit what you need in post production later. As long as you don't clip the red channel, there is plenty of detail and information to do whatever you need to do.

09-16-2015, 02:22 PM   #11
Pentaxian
emalvick's Avatar

Join Date: Feb 2008
Location: Davis, CA
Photos: Gallery
Posts: 1,474
I've not played too much or have had too many problems, but I've noticed that when I shoot RAW, the JPEG does tend to show more problems with reds than really exist with the RAW.

I also thought that RED was generally troublesome because of the way our sensors (And most digital camera sensors) are set up. There are fewer red sensors, so they fill up easily. What we shoot that is red tends to be bright anyway (like roses, fire engines, etc). Anyway, I don't use the multiple histogram option that we typically have while shooting (and I've quit pixel peeping since I moved on from my K10d), but if I spot a possible problem (qualitatively on visual inspection) during the flash up of the image, I do reshoot with a slight negative exposure composition just to make sure. Thankfully, I rarely find I am doing that, and most the time, the RAW file isn't as bad as the JPEG preview appears.
09-17-2015, 09:27 AM   #12
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,264
QuoteOriginally posted by mee Quote
detail in red seems to be a difficult choice for Pentax cameras..
...and Canon cameras and Nikon cameras and Sony cameras and Olympus cameras and Fuji cameras and Leica cameras...

They all use similar tech. The comments above regarding JPEG settings are useful, but the issue is with the actual capture at the sensor. The light-sensitive components are more responsive to the warm end of the spectrum. As noted above, the camera has compensating mechanisms but there are limits. With bright reds and yellows, the combination of high color saturation, bright light, and low subject contrast often results in low perceived detail and depth. Often enough highlight clipping may also be present in the red channel.

Shooting in RAW may help, but if the red channel highlights are clipped there is little that can be done in PP. The same is true for in-camera JPEG.

Edit: The struck-out text above is not true. I don't know where I got that idea. The actual sensitivity peaks in the green range with blue and red being about the same. As noted on other comments, the sensor uses filters and electronic trimming of the individual channels to approximate human vision. The ability to do this well is more difficult for red and to a lesser extent deep blues. Both colors can be problematic both for both high and low luminence.


Image lifted from a white paper on the Edmunds Scientific Web site.

Red: 620-750nm
Green: 495-570nm
Blue: 450-495nm

For a good discussion of actual spectral response:

LDP LLC: Spectral Response



Steve

Last edited by stevebrot; 09-17-2015 at 11:56 AM.
09-17-2015, 09:38 AM   #13
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,264
QuoteOriginally posted by Oricman Quote
This is the sort of thing image I get. The red can be so intense it bleaches out any detail. It's not a problem particular to Pentax - I've had reds pop out on most of my digital cameras.
I like your Crocosmia example. In many ways they are my nemesis flower, particularly the lucifer variety. The red is intense and very true and is painfully easy to block up. The below photo is a good example. I shot perhaps 20 exposures of this bunch of blooms, but only got four that were usable and that was shooting in open shade



Even so the backlit bloom at center right will appear blown on some monitors with some other displays showing artifact.


Steve


(...seriously considering HDR next time around...)

Last edited by stevebrot; 09-17-2015 at 11:58 AM.
09-17-2015, 09:51 AM   #14
Site Supporter
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 27,264
QuoteOriginally posted by stevebrot Quote
You can set the immediate preview image to include histogram data and set the playback mode display to include channel specific histograms. This should allow you to visualize the red channel clipping. Set the exposure comp down until the clipping is no longer evident.
I forgot to include a small caution. The in-camera histograms are based on the default JPEG settings. Be sure to have the "custom" option set to "natural" to avoid a misleading graph.


Steve
09-17-2015, 10:31 AM   #15
Site Supporter




Join Date: Jan 2010
Location: Michigan
Photos: Gallery
Posts: 2,168
Silicon absorption coefficient is lowest for the red filtered wells in the Bayer array, so it follows that red will have the worst signal-to noise ratio and the worst quantization jitter by the adc.
Also the Bayer sensor has a Nyquist on red annd blue that is only half of the green's Nyquist, so aliasing on red and blue will be more prevalent than on green, and sharpness will be worse than green.

When we open a camera raw file in an image processor on our computer , we may or may not be using the demosaicing coefficients provided for that camera by the camera manufacturer.
I read that some of these coefficients in the past have been developed by independent testers who provided the coefficients based on the "best" imagery.
Also when a new camera is released, how do we know what coefficients are being used for it by our older image processing application?
dcraw
https://www.cybercom.net/~dcoffin/dcraw/
In this link is the list showing the main photo image processors that use dcraw along with a list of supported cameras, but you would have to have a version of dcraw after the camera release.
(Note the comments by the author)

Some refs
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.187.5616&rep=rep1&type=pdf
LinuxPhoto.org
And Holst and Lomheim
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, cameras, channel, clipping, exposure, image, images, k30, pentax help, photography, troubleshooting
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Sony/Zeiss and Mamiya rumored to release medium format digital rangefinder cameras ogl Non-Pentax Cameras: Canon, Nikon, etc. 11 10-01-2014 10:36 AM
Canon Cameras Are Most Stolen Digital Cameras tomwil Non-Pentax Cameras: Canon, Nikon, etc. 6 12-18-2013 10:44 PM
All five new compact pentax digital cameras and select free shipping available just i Adam Homepage & Official Pentax News 2 11-10-2010 05:12 PM
Digital Cameras and obsolescence - planned or otherwise lesmore49 Photographic Technique 4 05-08-2009 03:02 PM



All times are GMT -7. The time now is 05:53 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top