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

[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.

[xnview]

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

[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

[foxyshadis]

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.