JPG lossless crop more accurate on right.
Moderators: XnTriq, helmut, xnview
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- XnThusiast
- Posts: 2443
- Joined: Sun May 15, 2005 6:31 am
JPG lossless crop more accurate on right.
With JPG lossless function, cropping a tiny number of pixels only from the right or bottom edges seems to work better than left or upper edges. So if you have a 1027x769 jpg, it can be chopped to exactly 1024x768 more easily from bottom or right edges. This seems like a feature and not a problem, so I hope this info is useful.
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- Posts: 7
- Joined: Sat Dec 25, 2004 9:06 pm
I guess that this has something to do with the IDCT algorythm of the JPEG-format, which allows to ignore some pixels on the bottom-right easier than at the top-left. I guess top-left pixels are processed first, but does this explain this behaviour??? Don't no.
While we are at, just some basics about the JPEG-format every moderate user of XnView should know:
-File is not saved in RGB, but in luminousity, saturation and color value (color vectors are first translated)
-Image is patterned in equally sized squares for luminousity, saturation and color value
-Okay, I spare you the details about DCT and IDCT (2 dimensional triangular wave functions (cosines))
-Saturations and colors are saved as IDCTs with size of 16x16 pixels, whereas only luminances are saved as more detailed IDCTs with size of 8x8 pixels
=> because you notice more details in luminance than in saturation or color
-Don't wanna explain Huffman table building...
While we are at, just some basics about the JPEG-format every moderate user of XnView should know:
-File is not saved in RGB, but in luminousity, saturation and color value (color vectors are first translated)
-Image is patterned in equally sized squares for luminousity, saturation and color value
-Okay, I spare you the details about DCT and IDCT (2 dimensional triangular wave functions (cosines))
-Saturations and colors are saved as IDCTs with size of 16x16 pixels, whereas only luminances are saved as more detailed IDCTs with size of 8x8 pixels
=> because you notice more details in luminance than in saturation or color
-Don't wanna explain Huffman table building...
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- XnThusiast
- Posts: 2443
- Joined: Sun May 15, 2005 6:31 am