Thank you for your answers.

I do understand the limitations brought about by printed media, but my use of Qimage is more to perform in-process flow manipulations of the type that can't be achieved else where. It was my hope that Qimage had a flag to save files in 16 or 32 bit per channel which minimize banding should the Qimage output file need processing with another image manipulation package afterwards.

With the 8 bit limitation in mind, I need to plan for Qimage being the final step post processing.

Sorry in advance if the has been discussed else where or if this is a RTFM subject.

When patch processing images and saving the output as newly created Tif format files, How can the bit depth be specified to be something other than 24 bits per pixel/8 bits per channel ?

For example, I just processed a set of images where originally 16 bit per channel and the saved Qimage output was 8.

Thanks Mike, sorry for not reading far enough in the manual.

I see I have a bit of math ahead of me, need to pull out the old books on solving simultaneous linear equations.

Mike, can you please clarify ?
Is the Current Color numerical values from the image file, memory resident with filters applied, or from the monitor values post Color Management gamut mapping ?

Thanks for the quick response Terry.

First of all, I do have my monitor calibrated, which I update about every other month.

I am not trying to set the Selective Color Table values by eye.

My work flow consists of:

Opening the image in Qimage with Create Associative Filter => Full Edit

I then use to cursor to examine each of the X-Rite ColorChecker primaries, recording the values that Qimage lists as "Curr. Color", which I'm assuming are the file values and not what XP sends to the monitor post color management.

I then do a bunch of calculations, dividing the X-Rite ColorChecker sRGB values by the measurements from Qimage to derive the Selective Color Table values.

For example, Qimage reports the "Curr. Color" of the Green square as [ 96, 146, 87 ], The ColorChecker target values are [ 70, 148, 73 ], so the conversion values needed by the Selective Color Table become [ 70 / 96, 148 / 146, 73 / 87 ] or [ 0.729167, 1.013699, 0.839081 ]

Now the problem comes when the reported "Curr. Color" contains a 0, Red being [ 164, 0, 56 ], and the ColorChecker target value is [ 175, 54, 60 ]. Calculating the Selective Color Table value ends up being [ 175 / 164, 54 / 0, 60 / 56 ] leaving the value for the Green channel effectively undefined. Tentatively, I've used the values of [ 1.067073, 1.0, 1.071429 ] knowing that this will leave the Red saturated.

This is a problem where Qimage uses the formula:

< Filtered Pixel Value > = < Selective Color Table term > * < Initial Image Pixel Value >

and not the formula:

< Filtered Pixel Value > = < Selective Color Table term > * ( < Initial Image Pixel Value > + < A Bias Value > )

If I could add a Green bias, lets say 10, across the whole image, I could create a Selective Color Table which would compensate and the math would work for the Red and Magenta to be on target.

Afterwards, I have no problem accepting that display or printing of an image will have the reproduced colors limited by the gamut mapping.

I'm new to the forum and been working my way up the Qimage learning curve.

My dSLR is a Sigma SD14 and I'm trying to achieve a high degree of image accuracy. I have a X-Rite ColorChecker which I have shot RAW in full Sun light with a Sunlight white balance.

Within Qimage, I am trying to create an accurate Selective Color Table. The problem that I'm having is the SD14 recorded the Red and Magenta squares Saturated, 165 0 58 and 194 0 161 respectively - Completely lacking anything in the Green channel. The sRGB target values for the X-Rite ColorChecker are RED: 175 54 60 and Magenta: 187 86 149, not what I'd call saturated colors.

Since the operation of the Selective Color Table is a pure multiplication, How do I add an appropriate Green bias selectively or to the overall image so I can have Green values to work with ?

The other X-Rite ColorChecker primary color squares, Blue, Green, Yellow, and Cyan each have Red, Green, and Blue channel values, so they are no problem to accurately alter with the Selective Color Table.

I know the SD14 tends to be Red sensitive, sacrificing the Green channel in the process. I also know the SD14 characteristically records intense, saturated, colors, but my goal with the Selective Color Table is to achieve a high correlation between the image and the actual scene.

As an aside, Why does the Embedded Image Information screen list the Depth for a RAW X3F file as 8 Bits when the SD14 uses 12 bit Analog to Digital converters ? Does this imply that Qimage lost some data along the way when the file was opened ?