Setting black & white point in curves

[taxboy]

I've just read that it is recommended to set the default target values in curves to RGB 5,5,5 and 250, 250, 250 to improve the image when setting black and white points.

Unfortunately there is no explanation why this should be so.

Can anyone explain please

 

[Richard]

I think it's something to do with printing. One of the PS books I have (which I can't find at the moment) says something about anything below 15 will always print at black, and anything above 240 will print as white. So if you do curves at 0 and 255 and print it, you'll get fewer details in the highlights and shadows than if you do it at 15/240.

 

[Chappers]

Richard is right.

What you are doing is setting the points at which the printer will produce either a black or a white, with detail .

The actual settings will depend on the exact printer / paper you are using. but 15/240 is a good start. You can make up a small test target in Photoshop, overlapping squares of different density. For the black set 0,5,10,15,20,25. For the white try 255, 250, 245,240, 235,230.Then print this normally

When you can just see a differentiation on the white, from the background paper white, that's you white setting. With the blacks it's similar but you need to see a difference between two patches.

Don't forget these setting will change with different papers and surfaces.

 

[taxboy]

Richard is right.

What you are doing is setting the points at which the printer will produce either a black or a white, with detail .

The actual settings will depend on the exact printer / paper you are using. but 15/240 is a good start. You can make up a small test target in Photoshop, overlapping squares of different density. For the black set 0,5,10,15,20,25. For the white try 255, 250, 245,240, 235,230.Then print this normally

When you can just see a differentiation on the white, from the background paper white, that's you white setting. With the blacks it's similar but you need to see a difference between two patches.

Don't forget these setting will change with different papers and surfaces.

Thanks for explaining this - I'll give it a go