Subtracting paper color from 4 color call-outs

[tmiller_iluvprinting]

Hello all,
I would like to ask if anybody has any experience subtracting paper color from 4 color call-outs. I have a job that will have 4 color swatches that will be printing on colored paper. In the past I have read the swatch samples with the Spectrolino to create my 4 color breakdown of the swatch. I then read the paper to get a 4 color breakdown of the paper, and I subtract this from the swatch breakdown to adjust for the color of the paper. This leaves a little to be desired to say the least. My question would be, would I be better off subtracting the Lab values of the colors and converting the difference to 4 color for the adjustment? As always, all input is most appreciated, and I thank you in advance.
Best regards,
Todd

[Lukas Engqvist]

Would it not be simpler to print a test chart and build an ICC? If getting correct result is what matters. When printing an IT reference you can feed various colours of papers and then you will have something to pick from.

[tmiller_iluvprinting]

Hello Lukas,
I have thought of this......but, the job is printing on a 6 different color papers (swatch book for a paper company) and time and materials are an issue. I subtracted the Lab values and converted the difference and the colors were quite accurate to my surprise! Thank you for your input.
Best regards,
Todd

[Tarun Chopra]

Hi Todd,

Its interesting to know this observation, you used the steps as as I understand:

a) Measure color (Lab) on colored paper
b) Measure paper color (Lab)
c) a (Lab values) - b (Lab values) = Resultant (Lab values) are converted to appropriate colorspace (ISO or whatever printing standard is used)

Regards

[tmiller_iluvprinting]

Hi Tarun,
a) Measured the color(Lab) of the customer supplied color swatch(printed on white paper.)
b) Measured the paper color(Lab.)
c) a*swatch-a*paper color=a*adjusted, b*swatch-b*paper color=b*adjusted (I left the L* of the color swatch alone.)
d) Entered the L*, adjusted a* and b* values in the Photoshop color picker with the desired CMYK profile loaded in Photoshop's color settings to arrive at the adjusted CMYK breakdown for the color swatches.
I must say the adjusted colors were quite accurate visually. I did not do any dE analysis.
Best regards,
Todd