I have two calibrated monitors and am submitting a book to Blurb. One monitor is brighter than the other--, that the images look fine on one and too dark on the other. I could changed the brightness, but how do I knwo which is correct for Blurb?what does Blurb see and do they correct images that are all too dark or too light?
Blurb does not correct anything in the uploaded pictures. This is stated clearly on their website; read up under <Color Management>.
It does not matter at all if your image looks fine on the monitor. What matters is if the color numbers of the image are correct. Blurb will print according to the color numbers.
The color numbers of your image will be displayed correctly on the monitor if it is properly calibrated to the industry standard of 6500 K and a gamma 0f 2.2 and if the intensity (brightness) of the monitor is set correctly.
Do this: calibrate both your monitors and set the target value for brightness (intensity) to a value between 100 - 110 cd/m2. This value is considered correct as it will give you prints that match the monitor in brightness.
The best test for checking for how images will look in a blurb book is this: Print the images as sRGB on your own printer. You can do this in two ways:
a) Export the image as JPG in sRGB in the size it will be printed. You can do this from the Book Module, Re-import it into Lr and print from Lr.
b) Don't export the image just print from Lr by selecting <Managed by printer> as the profile and set your printer to sRGB.