Image size in photoshop and other softwares [closed]

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I had to change the size of an image to 20 kb which was 46 kb earlier. I chose photoshop to do that. Followed a simple procedure, Image -> Image Size -> Edited the resolution and thus the image size changed. But the actual dimensions also changed which made the picture looked smaller.

I tried it on another software AAA logo. It worked like a charm! I just imported the jpeg image(which was 46 kb) and simply saved it. The size got reduced to 12 KB!

How does this work? Why does AAA logo automatically reduces the image size still keeping the same dimensions ? Can the same be done in photoshop too! ??

Answer 1

If by resolution you mean DPI then there are two different concepts in play.

First, in the world of images, or should I say, video and anything video-device (incl. bitmapped images, monitor and so on) DPI does not exist (there exist a misconception about this, even among professional designers).

In the world of video/image there only exist pixels and all images are measured in pixels. DPI is a pure arbitrary value, something Apple introduced in 1984 to target the DTP people.

As it is an arbitrary value it is up to the software to handle it or not. Photoshop clearly seem to adopt resolution in converting the pixel size as well which is actually incorrect but helps designers to cope with the DPI world (physical prints), while AAA then according to you doesn't which in case is correct way to handle images (DPI will be a descriptor to a layout program on how to scale it in relation to document DPI, but it won't change number of pixels in the image). This is a complicated and touchy area though (see f.ex. this page) so I'll leave the topic there :-)

Now, even so, the actual file size however is also influenced by compression ratio. My guess in this case is that you used a higher compression rate in AAA then in Photoshop. Try to use the same ratio in both to compare.

Answer 2

Use SaveAs->JPeg, Changing image size reduces only the dimensions of the image