Approximating RAW histogram

[tomczak]

Would it be safe to assume that if the WB is set to 'no WB', dynamic range = no change, and saturation = 0, the resulting Gray histogram approximates the value distribution (and physical maxing-out) of RAW values? If that's the case, what Saturation value would be useful to show the same, but for RAW R,G, and B channels separately (is it possible)?

Cheers!

[tomczak]

This is a somewhat related question on WB multipliers. Below are the standard multipliers of Canon S95. My understanding is that they represent how the RGGB RAW values are multiplied (using decimals) according to a respective WB setting. Why none of them (e.g. G) isn't set to 1.000 and the others scaled accordingly?

WB_RGGBLevelsAsShot : 1501 866 866 1885
ColorTempAsShot : 5943
WB_RGGBLevelsAuto : 1501 866 866 1885
ColorTempAuto : 5943
WB_RGGBLevelsMeasured : 1501 866 866 1885
ColorTempMeasured : 5943
WB_RGGBLevelsDaylight : 1541 870 870 1840
ColorTempDaylight : 6243
WB_RGGBLevelsShade : 1686 875 875 1682
ColorTempShade : 7323
WB_RGGBLevelsCloudy : 1686 875 875 1682
ColorTempCloudy : 7323
WB_RGGBLevelsTungsten : 1013 793 793 2518
ColorTempTungsten : 3619
WB_RGGBLevelsFluorescent : 1583 878 878 1836
ColorTempFluorescent : 6412
WB_RGGBLevelsKelvin : 1541 870 870 1840
ColorTempKelvin : 6243
WB_RGGBLevelsFlash : 1791 881 881 1563
ColorTempFlash : 8161

[gio]

Hello Maciej,
with rawdigger ( http://www.rawdigger.com ) you can analyze the raw data and view the histograms per channel.

From the website:
RawDigger is a computer program intended for viewing, studying, and analyzing raw files from digital photo cameras and some digital video cameras.

Regards
Johannes

[tomczak]

Many thanks, Johannes!

Here is an article on the topic, I found useful.

http://ninedegreesbelow.com/photography ... ml#clipped

But I'm still interested how to approximate a histogram of data actually clipped in RAW, using PWP histograms. Does the idea described above has virtue?

Cheers!

[den]

PWP's Raw Dialog is a mixture of raw conversion in the RGB color space model and editing features in either the HSV (default) or HSL color space models (except for the gamma adjustment and perhaps other features based on the RGB color space model) with 'removing artifacts', etc., during the progress of an APPLY or OK...

...so I am not so sure how well raw data is preserved or analyzed with the settings as suggested in the Original Post...

Perhaps a "dcraw.exe -v -a -H 1 -o 0 -W -6 -T" .....[messages; average the whole image for white balance; no Highlight clipping; raw Output color space; don't automatically brighten the image; output a 16 bit tiff]..... would be a better choice to preserve raw data for development and/or analysis.

The suggested Output tiff image would by default:
...(1) have a gamma 2.222 with a toe slope 4.5 (77.47 degrees);
...(2) an interpolation method preset for the camera model (Bilinear, VNG, PPG, or AHD);
...(3) a black level preset for the camera model; and
...(4) a saturation level preset for the camera model
with:
...(a) no lateral chromatic aberration correction;
...(b) no camera WB;
...(c) no chroma/luma noise reduction;
...(d) no tone/color/camera profiles; and
...(e) no dynamic range expansion.

For development, open the Output tiff in the PWP6 work space, then:
(1) adjust the White point for full range with a RGB BrightnessCurve and High Histogram;
(2) adjust the resulting (1) image mid-tone brightness with a RGB BrightnessCurve; and
(3) adjust the resulting (2) image for prefered lateral chromatic aberration correction, color, WB, noise reduction, and sharpening [Note: aggressive sharpening can increase or generate highlight and shadow clipping].

For analysis, use the PWP6 Histogram tool set for Luminosity and High Histogram and a RGB ColorCurves with a High Histogram to view specific R or G or B channel histograms. Both the Histogram Tool and ColorCurves can be open in the work space at the same time.

To locate highlight clipping, use a RGB BrightnessCurve or R or G or B ColorCurve = StairStep [0,0], [99,0], [99,100], [100,100]... similarly use a StairStep [0,100], [1,100], [1,0], [100,0] for shadow clipping locations.

[Note: usually I will map the 0-5% tone range for shadows and the 95-100% tone range for highlights to provide needed blending transistions should shadow or highlight clipping restorations be performed.]

Should analysis indicate needed changes in dcraw's black and saturation levels, these can be changed from their camera model 'default' values indicated in the dcraw Messages by adding options: " -k <num>" (Set darkness level) and/or " -S <num>" (Set the saturation level) where <num> are the new levels; to the previously suggested options... ...then re-run "dcraw.exe".

A freeware, Windows multi-threaded "dcraw.exe" is described with supported cameras and a download link here: http://www.heliconsoft.com/dcraw.html.

The above seemed to work as described for one trial Canon EOS-350D CR2 raw file dcraw conversion and PWP6 development/analysis. As the foregoing is based upon my current understandings/assumptions, any mistakes are my own and certainly not intended. If anyone has a differing understanding of 'dcraw' and PWP6, please advise...

...den...