Re: [Oiio-dev] Loading .CR2 raw image in right colorSpace (get rid of blue channel predominance)
I just noticed my command line isn't quite right... (in case anybody blindly tries what I wrote) you have to use -c and a redirection to a file to get a fully specifiable file name for the output file dcraw -4 -o0 -T -c /path/to/cr2 /path/to/output.tif or you can just run it dcraw -4 -o0 -T /path/to/file.cr2 and it will create a new file in the same path with the tif extension When running it it will perform no colour scaling and should leave the colour in the same colour space as the RAW file, so it is likely you will not get nice pictures, visually the saturation and hue will probably look odd because camera raw spaces are not display ones. You can specify an alternative colour space via the -o option Kevin On Mon, May 4, 2015 at 10:36 AM, Jerome Esnault esnault.jer...@gmail.com wrote: Hello, I tested the dcraw conversion and it gave me a darker result (whatever the colorSpace destination), so I assumed this is intrinsic to the camera sensor parameters and/or the picture was took within these conditions. If you want to test it, feel free to try my program from there : https://github.com/ejerome/CheckImgLinearity Thanks again, Best, Jeorme 2015-04-28 11:48 GMT+02:00 Jerome Esnault esnault.jer...@gmail.com: OK, thanks! It could be great if this could be part of the OIIO lib feature :) Many thanks. Best, Jerome 2015-04-22 12:17 GMT+02:00 Kevin Wheatley kevin.j.wheat...@gmail.com: using dcraw you can do something like... dcraw -4 -o0 -T /path/to/cr2 /path/to/output.tiff Kevin ___ Oiio-dev mailing list Oiio-dev@lists.openimageio.org http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org ___ Oiio-dev mailing list Oiio-dev@lists.openimageio.org http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org ___ Oiio-dev mailing list Oiio-dev@lists.openimageio.org http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org
Re: [Oiio-dev] Loading .CR2 raw image in right colorSpace (get rid of blue channel predominance)
OK, thanks! It could be great if this could be part of the OIIO lib feature :) Many thanks. Best, Jerome 2015-04-22 12:17 GMT+02:00 Kevin Wheatley kevin.j.wheat...@gmail.com: using dcraw you can do something like... dcraw -4 -o0 -T /path/to/cr2 /path/to/output.tiff Kevin ___ Oiio-dev mailing list Oiio-dev@lists.openimageio.org http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org ___ Oiio-dev mailing list Oiio-dev@lists.openimageio.org http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org
Re: [Oiio-dev] Loading .CR2 raw image in right colorSpace (get rid of blue channel predominance)
Hello, humm... Just whahou :) ! Many thanks for all your details. I wasn't aware of all the complexity of pixel color formats conversion. I don't know if I will have time to try your transformation suggestion (at some point I guess I will). I was wondering if this kind of transformation may alter the linearity of the image (just because of application of gamma)? Moreover, I thought about something/feature already available into OIIO or OCIO. I tried with imageMagick to display the CR2, and it seem to display well in the viewer but when I save back the image into PNG, the linearity of the image is completely broken. With OIIO the linearity is kept but I still have blue predominance (I guess the colorspace is still untouched sRGB). So, as my main goal is to process linear images, is it possible to convert my CR2 file into a PNG or a TIFF file keeping the linearity but with a different colorspace (to get rid of blue predominance) ? Many thanks again. Jerome 2015-04-20 22:05 GMT+02:00 Mark Visser mjmvis...@gmail.com: Good point, I assumed Jerome's CR2 files were in AdobeRGB (D65 white point). If they're in Adobe Wide Gamut RGB colour space (D50 white point), they'll require an additional transform between the two matrices: [CIE XYZ to sRGB] x [Von Kries D50 to D65] x [AdobeWideGamutRGB to CIE XYZ] On Mon, Apr 20, 2015 at 1:21 PM, Kevin Wheatley kevin.j.wheat...@gmail.com wrote: I'd like to add that you may also need to consider a Von Kries Ives style chromatic adaptation if moving between colour spaces with different white points see http://www.brucelindbloom.com/index.html?Eqn_ChromAdapt.html for an introduction. Kevin ___ Oiio-dev mailing list Oiio-dev@lists.openimageio.org http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org ___ Oiio-dev mailing list Oiio-dev@lists.openimageio.org http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org ___ Oiio-dev mailing list Oiio-dev@lists.openimageio.org http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org
Re: [Oiio-dev] Loading .CR2 raw image in right colorSpace (get rid of blue channel predominance)
Hi Jerome,
The problem you're encountering is that your .CR2 file is in a different
color space (AdobeRGB) from your display device (sRGB). In order to
properly view it, you will need to transform each pixel from AdobeRGB to
sRGB (which is exactly what the Windows viewer is doing). This is a linear
transformation, so can be represented by a multiply by a 3x3 matrix. Colour
transforms are usually represented in terms of matrices that go to and from
the CIE XYZ colour space, so you'll need two matrices:
pixel_in_XYZ = [AdobeRGB to CIE XYZ] x pixel_in_adobeRGB
pixel_in_sRGB = [CIE XYZ to sRGB] x pixel_in_XYZ
Matrix multiplication is associative, so you can simplify that to
pixel_in_sRGB = [CIE XYZ to sRGB] x [AdobeRGB to CIE XYZ] x
pixel_in_adobeRGB
*(pixels are assumed to be column vectors in RGB order)*
You can find the matrices you need on the wikipedia pages for AdobeRGB and
sRGB. Note that sRGB uses the same gamut as Rec.709 (also known as Bt.709).
*But wait, there's more:*
Before you transform your pixels from AdobeRGB to sRGB, you'll need to
linearize them. Adobe RGB uses a simple gamma of 2.19921875, so:
linear_pixel_in_adobeRGB = pixel_in_adobeRGB ^ 2.19921875
*(perform this computation on each channel independently)*
Putting this together, we've now got:
linear_pixel_in_adobeRGB = pixel_in_adobeRGB ^ 2.19921875
linear_pixel_in_sRGB = [CIE XYZ to sRGB] x [AdobeRGB to CIE XYZ] x
linear_pixel_in_adobeRGB
The final step is to convert this linearized sRGB pixel to a gamma-correct
sRGB pixel. sRGB has a wacky gamma curve that has a linear segment close to
zero. I'm just going to copy and paste from the wikipedia page (
en.wikipedia.org/wiki/SRGB):
[image: C_\mathrm{srgb}=\begin{cases} 12.92C_\mathrm{linear},
C_\mathrm{linear} \le 0.0031308\\ (1+a)C_\mathrm{linear}^{1/2.4}-a,
C_\mathrm{linear} 0.0031308 \end{cases}]
- where [image: a = 0.055]
*(again, apply the computation to each channel independently)*
So your final equation to go from AdobeRGB to sRGB is:
linear_pixel_in_adobeRGB = pixel_in_adobeRGB ^ 2.19921875
linear_pixel_in_sRGB = [CIE XYZ to sRGB] x [AdobeRGB to CIE XYZ] x
linear_pixel_in_adobeRGB
pixel_in_sRGB = C_srgb( linear_pixel_in_sRGB)
You can simply this further by pre-computing the matrix-matrix
multiplication.
If you don't really care about accuracy, you can also replace C_srgb() with
a simple gamma of 2.2:
pixel_in_sRGB = linear_pixel_in_sRGB ^ (1/2.2)
*(More details about this on the wikipedia page, but basically C_srgb
approximates a gamma of 2.2, but has a linear portion near zero to avoid
numerical problems.)*
All of these computations assume your pixels are floating-point in the
range [0.0, 1.0]. Also, note that the AdobeRGB gamut is wider (has more
colours) than that of sRGB, so you will need to clamp values to [0.0, 1.0]
after the matrix multiply.
You can also do all of this with OpenColorIO, but you'll need to create
spimtx files to go to/from AdobeRGB and add a color space definition. The
steps are essentially the same as above, but a somewhat higher level of
abstraction.
Hope that helps!
cheers,
-Mark
On Sat, Apr 18, 2015 at 2:18 PM, Jerome Esnault esnault.jer...@gmail.com
wrote:
Hello,
First of all, thanks for this great project :)
I'm trying to read and visualize a .cr2 image into my Qt application with
OIIO.
I implemented a QImage converter which work fine for jpg and png formats.
But when I open my cr2 picture, it seems the image have a predominance of
blue channel pixels...
If I open it with standard windows image viewer, it seems to be good
looking.
By opening it with another free trial image visualization software on
windows, I could saw 2 versions of this picture:
* the first one is the same strange blue image (marked as sRGB colorspace)
* the second one seems to be the right one I would excpected (more like
the jpg or png ones) which is marked as AdobeRGB colorspace
As I store an ImageBuf* of this picture, I tried to switch ColorSpace
sequentially (by pressing key c) with this snippet :
std::shared_ptrImageBuf ccSrc (d-mImgBuf); // color-corrected buffer
ccSrc-read(0,0,true,TypeDesc::FLOAT);
ImageBufAlgo::colorconvert(*ccSrc, *d-mImgBuf, current,
mColorSpace.toStdString() ); // whch could be Linear, sRGB or any available
OCIO ones like AdobeRGB
std::swap(d-mImgBuf, ccSrc);
But this have not effect anymore...
Same result if I try to use oiiotool : oiiotool picture.cr2
--tocolorspace Linear -o picture.png
(Note that the -o picture.CR2 doesn't work as OIIO couldn't find any
corresponding raw format to write it. Is that mean libRaw can read but not
write CR2 formats?)
This troubles is maybe due to the fact that any other ColorSpace I want to
use are not possible. The oiio error message is : Could not find ColorSapce
anyOtherColorSapceThanLinear...
I built OIIO with OCIO and set environement variable OCIO to
imageworks-OpenColorIO-Configs\aces_0.1.1\config.ocio.
I there anything else I
Re: [Oiio-dev] Loading .CR2 raw image in right colorSpace (get rid of blue channel predominance)
I'd like to add that you may also need to consider a Von Kries Ives style chromatic adaptation if moving between colour spaces with different white points see http://www.brucelindbloom.com/index.html?Eqn_ChromAdapt.html for an introduction. Kevin ___ Oiio-dev mailing list Oiio-dev@lists.openimageio.org http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org
Re: [Oiio-dev] Loading .CR2 raw image in right colorSpace (get rid of blue channel predominance)
Good point, I assumed Jerome's CR2 files were in AdobeRGB (D65 white point). If they're in Adobe Wide Gamut RGB colour space (D50 white point), they'll require an additional transform between the two matrices: [CIE XYZ to sRGB] x [Von Kries D50 to D65] x [AdobeWideGamutRGB to CIE XYZ] On Mon, Apr 20, 2015 at 1:21 PM, Kevin Wheatley kevin.j.wheat...@gmail.com wrote: I'd like to add that you may also need to consider a Von Kries Ives style chromatic adaptation if moving between colour spaces with different white points see http://www.brucelindbloom.com/index.html?Eqn_ChromAdapt.html for an introduction. Kevin ___ Oiio-dev mailing list Oiio-dev@lists.openimageio.org http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org ___ Oiio-dev mailing list Oiio-dev@lists.openimageio.org http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org
