Re: [Gimp-developer] Some questions about tiff

2022-09-18 Thread Liam R E Quin
On Sun, 2022-09-18 at 20:52 +0200, Adalbert Hanßen via gimp-developer-
list wrote:
> XSane produced a color scan from a document with 600 dpi and fill
> color, 
> 1.1MB file size.

I normally have XSane make a png file. For 8-bit per channel (0 to 255)
images, you can also use the XSane gimp plugin, which is a lot easier,
but make sure to export the file right away so you havwe a copy if gimp
crashes or if you make a mistake :)

> When I load this file into Gimp, I get an error message about an 
> incompatible TIFF format (additiona channels without the field 
> ExtraSamples). It gives me choice to let the additional channel worlk
> as
> 
> * non pre-multiplied alpha
> * pre-multiplied alpha
> * channel
> 
> I see no difference whatever choice I select.

If you choose Channel, it'll be visible in Gimp's Channels dialogue.
Otherwise, it's most like pre-multiplied alpha (transparency), and will
most likely be "all opaque", so you can ignore it.

> However: When I try to adapt colors by the contrast curve, I see no 
> Histogram under it.

How large is the image? If you used the Line Art setting in XSane every
pixel will be either 0 or 255, so the histogram is just two vertical
lines, one at eacn end, that aren't really visible as they're right
next to the edge. FOr a large image it can take a while for the
background thread to count all the pixels in the image and fill in the
histogram.


> ** Is this due to the error message when loading the file? **
no.


ankh / liam / demib0y

-- 
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[Gimp-developer] Some questions about tiff

2022-09-18 Thread Adalbert Hanßen via gimp-developer-list
XSane produced a color scan from a document with 600 dpi and fill color, 
1.1MB file size.


According to tiffinfo (under Xubuntu) the properties of the 
Sane-generatd tiff file is


TIFF Directory at offset 0x11af5a (1159002)
  Image Width: 4976 Image Length: 3190
  Resolution: 600, 600 pixels/inch
  Bits/Sample: 8
  Compression Scheme: JPEG
  Photometric Interpretation: YCbCr
  Orientation: row 0 top, col 0 lhs
  Samples/Pixel: 3
  Rows/Strip: 16
  Planar Configuration: single image plane
  Reference Black/White:
 0: 0   255
 1:   128   255
 2:   128   255
  Software: xsane
  DateTime: 2022:09:18 18:15:59
  JPEG Tables: (574 bytes)

When I load this file into Gimp, I get an error message about an 
incompatible TIFF format (additiona channels without the field 
ExtraSamples). It gives me choice to let the additional channel worlk as


* non pre-multiplied alpha
* pre-multiplied alpha
* channel

I see no difference whatever choice I select. But this might be due to 
my sample.


However: When I try to adapt colors by the contrast curve, I see no 
Histogram under it.


** Is this due to the error message when loading the file? **

I see histograms under the contrast curve for other tiff images not 
resulting from XSane.


Regards

Adalbert Hanßen



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