Question to "Origin"

[herb]

Hello Pierre,

XnViewMP version 1.00 has a tag "Origin" in: Info area --> tab properties --> images
My first thought was it is "Orientation" or similar, because for all my images "Top Left" is displayed.

Today I did a test with images that have different values for "Orientation".
BUT XnViewMP always shows "Top Left".

So my question is: what value is really displayed?

Thanks for your help in advance.
Best regards
herb

[xnview]

it's not always the orientation, but how the image is saved.

[XnTriq]

Is this the same bug as issue #915, herb?

• XnView Forum
  • EXIF orientation info is wrong
  • Question to various rotate
  • EXIF:orientation is always top-left(1)
  • "cmd_rotate" & "Change EXIF orientation ONLY"
• ImpulseAdventure: JPEG Rotation and EXIF Orientation
• JPEGclub.org: Exif Orientation Tag

[herb]

Hello Pierre, hello XnTriq,

thanks for your replies.

@Pierre:

it's not always the orientation, but how the image is saved.

Sorry, but I miss a scenario where this tag/value changes. Can you please give a detailed one.
My 2nd question is where is this value stored / taken from for display.

@XnTriq:
Sorry, I cannot answer your question. There are so many scenarions with orientation and I do not have the overview how XnViewMP should behave.

Best regards
herb

[xnview]

for example:

TIFF: it's the field orientation
BMP and other formats: often images are encoded bottom to top

[XnTriq]

for example:

TIFF: it's the field orientation
BMP and other formats: often images are encoded bottom to top

… like Truevision Targa:

• TGA image origin change
• Bottom-up checkbox option when saving in Targa (.tga) format
• Orientation of TGA generated by nconvert

Tools → Settings… → Formats → Write → TGA → Bottom-up orientation

Bit 4 of the image descriptor byte indicates right-to-left pixel ordering if set. Bit 5 indicates an ordering of top-to-bottom. Otherwise, pixels are stored in bottom-to-top, left-to-right order.

Thanks for clarifying, Pierre!

[herb]

Hello,

thanks for your quick replies.
But I am still confused:
Tag Exif:Orientation is used for the current orientation of the image.
As far as I know also in case of *.tiff or also *.bmp images.
Or do I miss somethings?

How can it be used for something like "but how the image is saved" (as Pierre wrote).
Thanks in advance for giving me more details.

I also did some experiments storing *.tiff images. But origin alsways was: Top left
Can you tell me the steps in order to get another value for "origin"

Best regards
herb

[XnTriq]

Does this answer (part of) your question, herb?

• Microsoft
  • Top-Down vs. Bottom-Up DIBs
  • Why are device-independent bitmaps upside down?
• Stack Overflow
  • Why do BITMAPS load "upwards"?
• Stack Exchange
  • Specific reasons why a top left origin is better/worse than a bottom left origin for computer graphics
  • Why is the origin in computer graphics coordinates at the top left?
  • Why do we use the top left corner as the origin in image processing?
  • Why is pixel 0,0 at the top left of some formats and bottom left of others?

Pixel grid origin = top/left:

Code: Select all

0 │  a  b  c  d
──┼────────────
1 │ 1a 1b 1c 1d
2 │ 2a 2b 2c 2d
3 │ 3a 3b 3c 3d
4 │ 4a 4b 4c 4d

Pixel grid origin = bottom/left:

Code: Select all

4 │ 4a 4b 4c 4d
3 │ 3a 3b 3c 3d
2 │ 2a 2b 2c 2d
1 │ 1a 1b 1c 1d
──┼────────────
0 │  a  b  c  d

[herb]

Hello XnTriq,

thanks for all the links. A very good private lession for me (although I have not read everything till now).
Things become clearer and clearer.

Best regards
herb