09-24-2018, 07:23 PM
(09-24-2018, 12:06 PM)Ofnuts Wrote:(09-23-2018, 06:57 PM)ajax Wrote: When saying "it doesn't involve conversion", might you mean during the editing session/process? It looks to me like I have to convert to 32bit floating point in order to put the image into that mode and then before exporting convert it back to some integer format if that is what I want (which I think might be necessary if I want a more universally supported image type).
Yes, currently there internal conversions happening for at least some operations.
In 32-bit FP you can still export to the usual formats without an explicit conversion. The only problem is that there seem to be a hard-wired correspondance between image precision in Gimp and the bitness of the TIF file.
I would expect that exporting to JPG would require conversion to 8bit precision but apparently TIF allows for 32bit FP which creates a file about twice the size of a pretty big 16bit TIF. Some viewers handle it others don't. This, 32bit FP TIF, might be useful as an intermediate file but NOT very desirable for finished product.
Some more experiments involved intentionally developing a raw image to be way overexposed. In that, plenty of clipped highlights which was then exported to a 16bit TIF. This 16bit TIF is then opened in GIMP and Image>Precision>32bit FP selected. I must admit that I don't know why I might choose Linear Light vs. Perceptual Gamma but for purpose of experiment tried both. However, NO clipped highlights show up when trying the following:
- Turn on View>Display Filter>Clip Warning (CW)
- Turn off CW and try View>Color Management>Soft Proof (SP) using the ICC profile for my calibrated display
- Change SP to use ICC profile for printer/paper
When I then convert it back to 16bit integer and SP now shows lots of clipped shadows but nothing for highlights when using the ICC profile for printer/paper. Changing to the display profile shows a very little bit of clipped shadows but still nothing for highlights.
While I'm pretty sure that the 16bit integer TIF file had lots of clipped highlights GIMP does undertake a profile conversion when loading the file. Doing the same thing but telling GIMP to KEEP the original profile when loading the file makes no difference. Is it possible that when loading an image file clipped pixels are converted to something, such as a maximum/minimum value, that is not clipped and that the only way clipping occurs in GIMP is by applying tools (i.e., processing) that causes it? When I open the overexposed file in Rawtherapee it has no problem recognizing and showing the clipping which of course it created.