How an 8bit image is processed?

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Simon
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How an 8bit image is processed?

Beitrag von Simon »

Hi,

If I have an 8bit TIFF. Why it becomes into a 24bit TIF after opening and saving it in PhotoLine.

1. I create an 8 bit TIFF in a RAW editor.
2. I open the TIFF in PhotoLine. The layer type shows RGB 8 bits.
3. I save the TIFF with no changes.
4. I open the TIFF in IrfanWiew and it is now 24 bits.
5. I open the TIFF in PhotoLine and it looks exactly as in point (2).

Why is this?

Thank you
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Gerhard Huber
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Re: How an 8bit image is processed?

Beitrag von Gerhard Huber »

Simon hat geschrieben: So 24 Sep 2017 07:09 If I have an 8bit TIFF. Why it becomes into a 24bit TIF after opening and saving it in PhotoLine.
does it really have 8 bit at all? Normally it means that it has 8 bit per channel, what is with 3 channels (R, G, B) 24 bit.
Simon hat geschrieben: So 24 Sep 2017 07:09 1. I create an 8 bit TIFF in a RAW editor.
2. I open the TIFF in PhotoLine. The layer type shows RGB 8 bits.
3. I save the TIFF with no changes.
4. I open the TIFF in IrfanWiew and it is now 24 bits.
if you open the TIFF from the raw editor, it is really 8 bit?

Gerhard
bkh
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Re: How an 8bit image is processed?

Beitrag von bkh »

Simon hat geschrieben: So 24 Sep 2017 07:09 Hi,

If I have an 8bit TIFF. Why it becomes into a 24bit TIF after opening and saving it in PhotoLine.
I guess that if you open the TIFF saved with your raw editor in IrfanView, it will also be shown as 24 bit TIFF (i.e., 8 bits times three channels). Afaik, there are no TIFFs with 24 bits per channel, just 8, 16 and 32 bits. Terminology differs a bit between apps.

Cheers

Burkhard.
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Hoogo
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Re: How an 8bit image is processed?

Beitrag von Hoogo »

I can think of 2 things when 8 Bit are mentioned:
-8 Bit grey scale. There's a layer mode in PL for that.
-8 Bit palette, 256 colors. I would be very surprised if there's no tiff for that. There's no palette layer mode, PL will open it as 24 Bit RGB, and I guess that's also how it will be saved - at least after you made changes to the layer.
But I don't know if the palette is really lost. "Colors > reduce colors" offers a palette named "Loaded", that should be the original palette. But I don't see document or layer properties about a palette, and I think it is not applied at all when saving as Tiff. Png offers the right options for a palette.
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bkh
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Re: How an 8bit image is processed?

Beitrag von bkh »

Hoogo hat geschrieben: So 24 Sep 2017 11:27 I can think of 2 things when 8 Bit are mentioned:
-8 Bit grey scale. There's a layer mode in PL for that.
-8 Bit palette, 256 colors. I would be very surprised if there's no tiff for that. There's no palette layer mode, PL will open it as 24 Bit RGB, and I guess that's also how it will be saved - at least after you made changes to the layer.
Indeed, there are TIFFs with 8 bit palette, and afaik, PL doesn't support saving TIFFs with palettes. (Saving 8 bit greyscale images shouldn't be a problem in PL.)

But I doubt that a raw editor outputs 8 bit (256 colour) palette images – reducing a photo to 256 colours normally leads to severe banding. I still suppose that this is just a matter of different terminology.

Cheers

Burkhard.