jpeg saved to black and white has a bigger file size??!!

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snorkyller
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Joined: Sat Mar 27, 2010 2:32 am

jpeg saved to black and white has a bigger file size??!!

Post by snorkyller »

Could you explain me this? :

I opened an jpeg image, did not make any change, just saved it to jpeg 50% quality. Result: 151ko

Then, I opened the same image, converted it to binary (no dither), and saved it to jpeg 50% quality. Result: 204Ko

:?: :?: :?: :?: :?: :?: :?: :?: :?:

I thought I would decrease the image size by reducing the number of colors.
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xnview
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Joined: Mon Oct 13, 2003 7:31 am
Location: France

Re: jpeg saved to black and white has a bigger file size??!!

Post by xnview »

snorkyller wrote:I thought I would decrease the image size by reducing the number of colors.
JPEG can't save black&white picture so the picture is converted in greyscale
Pierre.
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oops66
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Joined: Tue Jul 17, 2007 1:17 am
Location: France

Re: jpeg saved to black and white has a bigger file size??!!

Post by oops66 »

Hello,
Maybe you can use a pluggin like: Ximagic GrayDither toolbox

http://newsgroup.xnview.com/viewtopic.php?f=38&t=16977
http://www.ximagic.com/

Ximagic GrayDither toolbox
XnViewMP Linux X64 - Debian - X64
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foxyshadis
Posts: 387
Joined: Sat Nov 18, 2006 8:57 am

Re: jpeg saved to black and white has a bigger file size??!!

Post by foxyshadis »

snorkyller wrote:Could you explain me this? :

I opened an jpeg image, did not make any change, just saved it to jpeg 50% quality. Result: 151ko

Then, I opened the same image, converted it to binary (no dither), and saved it to jpeg 50% quality. Result: 204Ko

:?: :?: :?: :?: :?: :?: :?: :?: :?:

I thought I would decrease the image size by reducing the number of colors.
That only works for lossless formats - bmp, png, gif, etc. All it does for jpeg is screw it up completely. Never reduce colors or dither a jpeg - or save it as another format if you need to.