Underexposing does not recover clipped highlights

Hi!

I have an image that has few spots that are clipping and I'm trying to use the exposure correction and stop it down by 2 stops (0.25). However the image it returns has all the clipped whites that used to be at 1.0 at 0.25. If I do the same with Lightroom or Photoshop, there's more detail in the highlights showing up with values above 0.25.

These are my parameters:

imgdata.params.output_bps = 16;
imgdata.params.bright = 1.0;
imgdata.params.gamm[0] = 1.0;
imgdata.params.gamm[1] = 1.0;
imgdata.params.no_auto_bright = 1;
imgdata.params.use_camera_wb = 1;
imgdata.params.highlight = 0;
imgdata.params.output_color = 1;
imgdata.params.use_rawspeed = 1;
imgdata.params.exp_correc = 1;
imgdata.params.exp_preser = 0;
imgdata.params.exp_shift = 0.25;

What am I missing?

Thanks,

Nhat

Forums: 

If you data is already

If you data is already clipped, the exposure correction will not help.
You may try to use highlight recovery (slow!), but it will help only if some details exists in some channels (e.g blue or red)

-- Alex Tutubalin

Thanks for your reply Alex!

Thanks for your reply Alex!

I was wondering why there's so much more definition if I expose the same raw file down using lightroom?

Thanks a lot,

Nhat

Lightroom tries to recover

Lightroom tries to recover highlights (i.e. modulate overexposed channel by differences in lower exposed channels) automatically.

You may try to use our RawDigger software ( www.rawdigger.com/download ) to explore the raw data histogram and see is real data clipping exists

-- Alex Tutubalin

Libraw's -4 option is different from dcraw's -4 option

Test:
(v. 0.16)
dcraw -4 -T filename.nef
dcraw_emu -4 -T filename.nef

produces different results, as does the '-W' option (which is also enabled when using -4 option).
Could it be that there is still some kind of auto scaling enabled within dcraw_emu, because it brightens consequtive images differently some times, while dcraw does not.