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Suboptimal algorithm JPG


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I take an image in JPG format. Image made probably in another editor. File size is 45 KB.

I choose the menu item "Save as". I choose the JPG Format image again. New file size is 52 KB.

Do you think that it's not essential? Then the absurd example. Take the same image. Let me remind you that its size is 45 KB. Image size is 900x675. I select the rectangular area in the center of the image. The size of the area is 677x523. Ctrl+Shift+X and save image. Do you think the size of the image become less? New file size is 56 KB. wacko.gif

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It will be roughly 95% of the quality of the original, but the file size will still be (roughly) the same as if the original was saved at 95%.

You think that from the original image quality 10% can be restored image quality with 100%? Logical to assume that the quality of the original image is 100% ap.gif

Edited by xmario
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That is, paint.net can improve bad quality? You think that this is possible? shok.gif That is, an source image with poor quality stores information about perfect quality? ap.gif

If you open an 80% quality image, add a drawing on a new layer and save it as a 95% quality JPEG the file size will be larger and the drawing will be only slightly distorted, but the old image won't get any better.

KaHuc.png
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If you open an 80% quality image, add a drawing on a new layer and save it as a 95% quality JPEG the file size will be larger and the drawing will be only slightly distorted, but the old image won't get any better.

If you've read the first message - I DON'T add a drawing. I only save an original image with the same format.

When I open a text document in Notepad and save it without editing, I get the same file size. It is logical to expect the same result from the image editor... bt.gif

Edited by xmario
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If you've read the first message - I DON'T add a drawing. I only save an original image with the same format.

When I open a text document in Notepad and save it without editing, I get the same file size. It is logical to expect the same result from the image editor... bt.gif

File size is not the same as quality. The quality slider determines how much quality will be sacrificed in this save. Any quality you have lost before is gone forever and you can't even keep the benefit of a smaller file size.

Once you open a JPEG image it's converted into a bitmap and any quality loss is similar to quality loss resulting from a scanned photo being torn. It may be a lower-quality image to anyone that sees it (just as it would be a low-quality image if it was taken with a shaky camera), but that doesn't mean it has a smaller file size.

KaHuc.png
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File size is not the same as quality. The quality slider determines how much quality will be sacrificed in this save. Any quality you have lost before is gone forever and you can't even keep the benefit of a smaller file size.

Once you open a JPEG image it's converted into a bitmap and any quality loss is similar to quality loss resulting from a scanned photo being torn. It may be a lower-quality image to anyone that sees it (just as it would be a low-quality image if it was taken with a shaky camera), but that doesn't mean it has a smaller file size.

By converting JPG bitmap-JPG are inevitable loss of quality?! OK, then why for JPG files created in paint.net it is not so? Make an JPG file with paint.net. Open it again. Save it as another JPG file without editing. Changing the file size will be minimal...

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