I On Wed, 26 Jan 2022 at 13:55, Top Rock Photography < ka...@toprockphotography.com> wrote:
> >…the image seems to be just fine at the end of my pixel pipeline. >> (Truth be told, I do not actually know what would happen IF I dropped the >> blacks into the negative). > > > I just did some experimentation, and I found out that some really bad > stuff happens when the numbers go negative, (depending on how the image is > exported), when I examine the areas outside my subjects which were clipped > into negative values. > > As WebP, all the negative values seem to clip at zero. Any number that was > not negative has a real, non-zero value. The result is that, as one > approaches the darker part of the image, there is a sudden change from > nearly black to pitch black. > > As AVIF, this phenomenon seems to disappear almost entirely in 8-bit mode, > and virtually gone in 12-bit mode. > > As JPEG-JFIF, the issue affects more than just near-black to black, but > also other hues in the shadows, making sudden jumps from, say, a dark > shade of green, to perhaps a dark shade of maroon, to pitch black . This, > of course, may be because the JPEG-JFIF compression algorithm favours > colour accuracy in the highlights versus the shadows. > > Nevertheless, crushing the blacks into negative values may have undesired > consequences. I may not have noticed before due to one or more of the > following > > 1. the clipping was never on my subject, so not really noticed. > 2. I mostly export to WebP > 3. Our eyes see more details in the midtones/highlights, and our > brains filter-out/fills-in the details of the shadows, so the phenomenon is > not noticed. > > I must say, though, on the JPEG-JFIF, it was obvious to me. (On the > others, I had to specifically study the shadows to notice). > > Sincerely, > > Karim Hosein > Top Rock Photography > 754.999.1652 > > > > On Wed, 26 Jan 2022 at 00:45, Top Rock Photography < > ka...@toprockphotography.com> wrote: > >> >>> >> Whatever the reason, so long as I do not end up clipping (crushing) my >> shadows in the [exposure] module into negative values, the image seems to >> be just fine at the end of my pixel pipeline. (Truth be told, I do not >> actually know what would happen IF I dropped the blacks into the negative). >> >>> >>> > ____________________________________________________________________________ > darktable user mailing list to unsubscribe send a mail to > darktable-user+unsubscr...@lists.darktable.org > -- I have never understood floating point. But if I follow what has been written here the darkest pixel is assigned a value of 0 and the brightest pixel is assigned 1. Then all the other pixel values fall between 0 and 1 until you export as a 8 or 16 bit image. Am I understanding this correctly? ____________________________________________________________________________ darktable user mailing list to unsubscribe send a mail to darktable-user+unsubscr...@lists.darktable.org
