At http://depositfiles.com/files/qy1a48oal you can download a series of
tests with vuescan (same files as mentioned in "Cannot laod DNG-file
from Vuescan"). And now I try to find out with these files, what is the
best format for darktable?
If someone has problems with the download, let me know, and I will give
you an url to my homepage, with limited bandwidth.
The goal is to use a file with the best quality (lossless) and the best
compression, so the smallest filesize is used.
With my sample scans I got:
series2:
color:
uncompressed tiff:
36M series2_scan-130414-0001.tif
36M series2_scanraw0001.tif
exiftool -Compression series2_scan-130414-0001.tif
Compression : Uncompressed
exiftool -Compression series2_scanraw0001.tif
Compression : Uncompressed
identify -verbose series2_scan-130414-0001.tif
Image: series2_scan-130414-0001.tif
Format: TIFF (Tagged Image File Format)
Class: DirectClass
Geometry: 3037x2066+0+0
Resolution: 600x600
Print size: 5.06167x3.44333
Units: PixelsPerInch
Type: TrueColor
Base type: TrueColor
Endianess: MSB
Colorspace: RGB
Depth: 16-bit
Channel depth:
red: 16-bit
green: 16-bit
blue: 16-bit
...
So we have a colorscan with 48bit.
If I convert these files to png (lossless, compression options -quality
90) I get
30M series2_scan-130414-0001.tif.png
18M series2_scanraw0001.tif.png
So you see the raw-file of vuescan was compressed a lot more than the
normal file.
I am not sure, but as I understand vuescan, you can use a
"vuescan-rawfile" to modify the image without scanning again. So it
should be possible to create series2_scan-130414-0001.tif from
series2_scanraw0001.tif and series2_scanraw0001.tif should be the file
which should be used with darktable, since it is a lot smaller. But I
have to say, I couldn't produce a similar image to
series2_scan-130414-0001.tif created from series2_scanraw0001.tif as
source with darktable (but I am a dt newbie)
The 2nd best way, would be to use a tiff-file, which was compressed by
vuescan. (series3)
41M series3_scan-130414-0001.tif
36M series3_scanraw0001.tif
exiftool -Compression series3_scan-130414-0001.tif
Compression : LZW
exiftool -Compression series3_scanraw0001.tif
Compression : Uncompressed
Hey that's really strange, the LZW compressed file is bigger than the
uncompressed file and bigger as the raw file. Ok that's a different
scan, but with the same settings as before. Only the compression was
changed. Please see screenshots of the settings.
identify -verbose series3_scan-130414-0001.tif
Image: series3_scan-130414-0001.tif
Format: TIFF (Tagged Image File Format)
Class: DirectClass
Geometry: 3037x2066+0+0
Resolution: 600x600
Print size: 5.06167x3.44333
Units: PixelsPerInch
Type: TrueColor
Base type: TrueColor
Endianess: MSB
Colorspace: RGB
Depth: 16-bit
Channel depth:
red: 16-bit
green: 16-bit
blue: 16-bit
It looks different with b&w scans.
series5
black and white, uncompressed
12M series5_scan-130414-0001.tif
12M series5_scanraw0001.tif
exiftool -Compression series5_scan-130414-0001.tif
Compression : Uncompressed
exiftool -Compression series5_scanraw0001.tif
Compression : Uncompressed
identify -verbose series5_scan-130414-0001.tif
Image: series5_scan-130414-0001.tif
Format: TIFF (Tagged Image File Format)
Class: DirectClass
Geometry: 3037x2066+0+0
Resolution: 600x600
Print size: 5.06167x3.44333
Units: PixelsPerInch
Type: Grayscale
Base type: Grayscale
Endianess: MSB
Colorspace: RGB
Depth: 16-bit
Channel depth:
gray: 16-bit
Channel statistics:
Gray:
min: 8027 (0.122484)
max: 65535 (1)
mean: 36400.8 (0.555441)
standard deviation: 15888.2 (0.242439)
kurtosis: -1.19674
skewness: -0.0278737
So we have a scan with 16bit gray.
If I convert these b&w files to png (lossless, compression options
-quality 90) I get
4,3M Apr series5_scan-130414-0001.tif.png
4,5M Apr series5_scanraw0001.tif.png
So there is a lot more harddrive space saved than with a color scan,
but while the tif-files are nearly identical, the "raw-png-file" is
less compressed than the "normal" one.
Series 6 shows the compressed tif-version:
6,2M series6_scan-130414-0001.tif
12M series6_scanraw0001.tif
exiftool -Compression series6_scan-130414-0001.tif
Compression : LZW
exiftool -Compression series6_scanraw0001.tif
Compression : Uncompressed
Obviously all raw-vuescan-scans are uncompressed and the
output-compression-settings are not used for "raw".
So IMHO it would be best to use png-files for darktable to improve the
scan, but what is not clear, if the color-png-file should be used, that
was created by "raw-vuescan-scan", while with b&w it is better not to
use the "raw-vuescan-scan", but the "normal" scan.
I would be happy the hear any suggestions from you. I would like to
scan a lot of paper photos, not slides or negatives at the moment. And
there is a huge difference in filesize, depending which image-format is
used.
--
Αl
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