Re: [Gimp-developer] Some questions about tiff

[Liam R E Quin <liam holoweb net>]

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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