- Oct 10, 2003
Am făcut asta şi sunt identice. În plus,
http://en.wikipedia.org/wiki/Jpeg#Lossless_editingA number of alterations can be performed to a JPEG image without any quality loss. Blocks can be rotated in 90 degree increments, flipped in the horizontal vertical and diagonal axes and moved about in the image. Not all blocks from the original image need to be used in the modified one.
The top and left of a JPEG image must lie on a block boundary, but the bottom and right need not do so. This limits the possible lossless crop operations, and also what flips and rotates can be performed on an image whose edges do not lie on a block boundary for all channels.
It is also possible to transform between baseline and progressive formats without any loss of quality, since the only difference is the order in which the coefficients are placed in the file.
Furthermore, if a JPEG is decompressed, edited, and then recompressed using the same chroma subsampling and quantisation tables, then unedited areas of the image should have minimal quality loss.
When using lossless cropping, if the bottom or right side of the crop region is not on a block boundary then the rest of the data from the partially used blocks will still be present in the cropped file and can be recovered relatively easily by anyone with a hex editor and an understanding of the format.