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maderic
Joined: 28 May 2005
Posts: 4
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 Posted: Sat May 28, 2005 12:47 pm Post subject: Why does save as jpeg option 12 increase file size |
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I'm really confused about this. I can take a jpeg file of around 1MB make a jpeg copy of it compression level 12 (maximum quality) and the resulting file will be nearly 2MB in size.
I thought that jpeg was supposed to compress files. I expected this setting of 12 to be almost exactly the same size or marginally smaller but not almost double the size
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| Posted: Sat May 28, 2005 1:18 pm Post subject: |
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Higher quality means more details which means a bigger size. |
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maderic
Joined: 28 May 2005
Posts: 4
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| Posted: Sat May 28, 2005 1:26 pm Post subject: |
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Yes I understand that but how can you end up with nearly double the data when of the original when jpeg is supposed to compress? What additional data has been added to the original?
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| Posted: Sat May 28, 2005 2:10 pm Post subject: |
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| maderic wrote: | | What additional data has been added to the original? |
The number of pixels of the same color. Jpeg averages color in arrays of pixels. Let's say that the Jpeg setting medium averages the color in a 5x5 array. All it needs to remember is the color and sometimes the number of arays that follow each other up with the same color.
With 100x100 pixels means it has to store 20x20=400 times the color information of an array.
If you go for a higher quality, then you have smaller arrays, so in the case of the 100x100 image it could mean with an array of 2x2 = 25x25= 625 times the color information of an array.
625 is larger than 400 so that explains the size. There is a bit more to it and the number won't be exactly 625 but slightly lower, but this is where you have to look to understand the whole concept. |
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