Resizing up and comparative file size

[dguire]

Hello, I am in the process of resizing around 20 photos to larger dimensions for printing purposes. I am inputting the width and allowing the height and resolution to self adjust. In each case no other adjustments are made to the file and I am not resampling.

When I compare the original file size to the resized file, all resizes are larger except for 3 photos. Is that normal? The actual file being larger makes sense to me as I am increasing the size. What concerns me on the files that are smaller is am I losing some quality on my prints?

Thanks,
Donald

[Wendy]

Hi Donald ..

... and welcome to the forum :)

The larger size is probably simply down to a different compression rate between the original jpg and the one you have just saved :)

Wendy

[dguire]

Wendy,

Thanks for the welcome and the reply. What about the 3 photos where the upsized file is smaller than the original? Should I have concerns about image quality on the prints?

Donald

[NickLewis]

Hi Donald,

The increase in file size is nothing to do with your change to the width - because you aren't resampling, you have the same pixels in the resulting file as you started with - just a different description of how big the image should be when printed. As Wendy says, the increase in size is due to a different compression algorithm and quality setting.

File sizes will vary between images. Achieved compression ratios aren't constant, even at the same quality settings - it depends on the amount of detail in the image. The less detail, the more the image can be compressed.

Are the smaller photos less complex images, by any chance? That is, containing less detail, possibly with large areas of flat colour.

Nick

[dguire]

Nick,

Yes the images which have saved into smaller file size are less complex with broad areas of same colors.

Thanks for the help.

Donald

[NickLewis]

Whew! That's a relief - I was dreading you saying it was the other way round!! :)

Nick