02-17-2020, 08:04 AM
(02-16-2020, 09:12 PM)ajax Wrote:(02-16-2020, 01:23 PM)Ofnuts Wrote: Which Gimp version? What settings? On my Gimp 2.10.14, with no compression, a 400x400 image with a single layer without alpha channel exports as a 664K file, and reloads in Gimp without getting an alpha-channel. Adding an alpha-channel makes it a 820K file.
Edit: this is confirmed by ImageMagick's identify that says: tiff:alpha: unspecified for the image without alpha and tiff:alpha: unassociated for the image with alpha.
PS: Can you attach a (small) TIFF from an image without alpha channel in Gimp?
GIMP 2.10.12 is the newest I have. However, this phenomenon has been going on for a long time that I've been using GIMP and certainly has existed in all of the 2.10.? versions I've used which is probably at least 5 different releases.
When exporting to tif I specify no compression, include all metadata, uncheck save layers and save thumbnail.
With GIMP I can create a small (400x400) image by copying such a selection from a real picture. However, because I'm doing this with GIMP I have no way of opening such a file that was NOT created by GIMP. I do notice when I create a new 400x400 image, with transparent background, GIMP says it has an alpha channel. So I pasted the 400x400 selection copied from another image and then deleted the alpha channel. When I export that as tif the result is a file that is 626.04KB according to XnViewMP. Apparently that is too big to be attached here. However, I can take that file and open it in Rawtherapee (5.4) and export it from there in tif format which produces a file that is 493.93KB which is attached. If I then open that file in GIMP it indicates that there is no alpha channel. However, if I now open the file created by GIMP in GIMP it says there is an alpha channel even though as stated above I purposely deleted the alpha channel before exporting.
Another factor is that of the 2 files referenced above the one created by GIMP cannot be opened by the software supplied with my cameras, Canon Digital Photo Profession R4 (DPP4), whereas the file created by Rawtherapee can be opened and processed normally by DPP4.
The file created with RT doesn't help. If the file is too big use a smaller image.
- Created a 100x100 image (10000px) without an alpha channel. Filled with "Plasma".
- Export as TIFF, no compression , all default settings, except skipped the thumbnail.
- Exported TIFF is 30990 bytes (so roughly 3 bytes/pixel)
- Layer>Transparency>Add alpha channel
- Export as TIFF, no compression , all default settings, except skipped the thumbnail.
- Exported TIFF is 41007 bytes (so roughly 4 bytes/pixel)