I got a picture of 4kb, and used photoshop(cs4) to paint white all,so it changed to white rectangle, then saved it.
that's for web site logos, so it must keep the picture size same as original (ex, 70px * 50px).
The problem I have was, the saved picture(with png, jpeg, gif, or any format) has a size of over 40k bite.
This is rediculous, so, please tell me how to make the file size at most the original size, i.e. 4kb by using Photoshop, if it is possible.
If you're trying to minimize the size of a JPEG consider using File - Save for Web and disabling the writing of all Metadata. You could also instruct Photoshop to save the image without an embedded color profile for some additional savings.
But you might want to consider saving instead as a PNG file, which would get you an even smaller file size. I was able to save a pure white PNG-24 file with 600 x 400 pixels that takes 1,324 bytes.
I didn't see how to disable the writing of Metadata and embedded color profile, but I could manage to save it with 141byte(for png) and 551byte(for jpeg) using web save function.