Photo editing advice please.........

alison74

I have been editing photos on the comp and edited a pic down from 1.8mb to

816 kb ( 1136 x 1430 ) which should print out at 7 x 5 ok.

I then want to turn the pic into black and white aswell, which I did using Picasa and it has come out at 235kb (1136 x 1430)

My question is this ? Because it's black and white, does it use up less memory i.e why is it now 235kb for the pic when I only changed the colour. Will it still print out ok ?

This is my first time at changing colour into B & W and would be grateful for advice before I spend an hour changing others !

Hope I have made myself clear, thanks in advance

espresso

Yes it's quite normal for a black & white picture file to be much smaller. Basically in a B & W picture, each pixel is either black or white (1 bit per pixel) to make up a grey-scale picture, whereas in a colour picture the colour depth per pixel could be 256 colours or 8 bits per pixel. i.e. a lot more information!

If you have not tried Irfanview, it's well worth downloading and it's free.

:T

alison74

Thanks for that, so does that also mean a B & W pic on a camera take up less room

i.e 200 colour pics on memory card = 400 or so B & W pics on memory card ?

oldwiring

BTW this is a related thought about converting colour to B&W (really grayscale I think),
You may need to adjust the brightness and contrast on the result to get satisfaction. Trouble is I can't recall what I was told to do.

mikemoate

I actually think you need to be careful. I'm not familiar with Picasa however some imaging programmes actually have in-bullt compression factors when saving photo's you have edited. That is they assume you want to reduce image size and hence quality and use automatic settings to do this. I converted a colour image to b/w using paint shop pro with no compression and whilst the image size in mb was smaller it was by a much lesser ratio than the one you obtained in Picasa. i would check in Picasa if there is a pre-set compression factor.

alison74

[QUOTE



i would check in Picasa if there is a pre-set compression factor.[/QUOTE]

Where would I find this out ??

I know that when you email from picasa it shrinks from whatever size the orginal is to 60-70k so perfect for emailing.

mikemoate

As i said i'm not familiar with Picasa (note to self - have a look at it) but I did find this on the web, hope it helps,

"It seems that when you alter a picture using Picasa, the new copy that it saves is considerably smaller than the original - a 3.3mb jpeg that i just cropped slightly, when i saved a new copy after the alteration, it ended up being just 378k. is there anyway i can avoid losing all that information when i save after editing in picasa? thanks for your responses."

"I think I found the solution to the problem - if you use the "Export" option instead of "Save a copy" Picasa provides a choice of compression levels."

alison74

Thanks for that last tip. There is an option in 'export to folder' to use orginal size, or downsize them to 800 pixels (or lower)

F1F1

If you're saving a jpg, then doing something to it <such as converting to b&w> and saving again, it will be compressing the image each time, reducing the quality and thus reducing the file size. Jpg is a lossy format - which means that you lose quality when you save it.