Setting black & white target values in curves

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

It leaves you some "fudge factor" or headroom where the top and bottom of your dynamic range are not absolutes.

Unfotunately this advice has been passed down through numerous Photoshop books and has become the "accepted wisdom" with few people even questioning why. Thankfully most of the newer books no longer include this misleading advice because its not correct in the majority of cases.

Setting target values in Photoshop to numbers other than 0 or 255 is applicable only if you intend to PRINT a particular image. Since most people do not print their images its best to leave the settings at 0 and 255 so as to take advantage of the full gamut of your monitor. Only make the adjustment for images destined for printing. Unfortunately the Photoshop books I've seen, and I've read many, do a poor job of communicating that this advice is only relevant for prints.

For an excellent discussion of this subject see this link: Black/White Clipping Points
Oops...the link doesn't take you all the way to the relevant page. Click on Color Correction > Black/White for the explanation behind why you shouldn't adjust your clipping points unless printing.

To quote: "Several authors recommend increasing the black point, and decreasing the white point, without calibration. In many cases, and indeed for the Fuji Frontier, results obtained will resemble the wimpy photographic papers from the 50's."

Taxboy wrote in post #5217329
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

Artistic interpretations aside, why would you purposely want to make your black detail at 0 (no detail, just pure black), and your white detail at 255 (just pure white, no detail), regardless if you're going to be printing or not? Most photographers I know DO print in one form or another. Blowing out your highlights or washing out your shadows isn't going to help in the long run.

I do agree with you in regards to the printing, but this isn't just limited to printing. You CAN see a loss of detail when you push your highlights and shadows too far.

If you properly expose your images it wouldn't matter, would it? Setting your blacks to 0 obviously doesn't mean that all your blacks wouldn't have detail if the image is correctly exposed. Setting your black point in Curves or Levels to a number greater than 0 means you're effectively changing the color to a dark grey. And now there are several tools available that work better than adjusting clipping points: The Shadow/Highlight tool in Photoshop, especially when used in conjunction with Smart Object layers; and the Fill Light tool in Lightroom. Using those tools means that only your absolute blacks will appear as such on your monitor.

I agree with Fedka. I set my endpoints to 0 and 255, and my clipping really really low - 0.01%