A very naive Newby Q

[miatab]

I need to produce jpeg images that are 1800 X1200 pixels, and less than 3.0 mb. Is Resolution chained to file size? I routinely import 9.5 mb images into Photos, but when I export and save these images for exhibition, they are never close to the 3.0 mb limit for 1800X1200 pixel images. What am I in my ignorance doing wrong?

[dje]

Hi Ken

Yes pixel dimensions do have an effect on file size. Your 9.5MB images would have pixel dimensions much higher than 1800x1200 so you need to resize them down. I assume you are using Photos for Mac. I'm not a mac user but my daughter has one and I believe you can resize images on Export. I'm afraid I can't help you with detailed directions though. The procedure probably depends on the version you are using.

An 1800 x 1200 jpeg with quality set to second highest should bring the file size down to well below 3MB.

Dave

[Black Pearl]

Chose the image you want to re-size in Photos.

Go to File - Export - Export 1 Photo

Click on the little Arrow to the right of Photo Kind - JPEG

This will give you a series of options including Size which you need to use the drop down menu to change to Custom.

You can now input the Maximum Width - 1800 in your case - and have a play around with the JPEG Quality settings to get a file under 3MB though I'd imagine just leaving it at High should be perfectly fine. You can also re-name the image and point to where you want it saved.

[pnodrog]

The jpeg file size is determined by a mix of image size, image content and quality setting. The more detail in the image (including colour variations) the larger the jpeg file provided the image size and quality remains the same. Test an image with half blue and half red and compare it with one that has a gradient from blue to red and you will see the file size of the gradient image is larger.

[pnodrog]

Below are small versions of what were 1200x1800px images saved at quality 10 with photoshop.

Original jpeg size 75Kb


Original jpeg size 107Kb



Original jpeg size 133Kb

[DanK]

I think this can be simplified. I don't use that software, but the basic steps are these:

1. Export or save the file as a jpeg with the size specified in pixel dimensions (1800 x 1200) and jpeg quality set to the maximum (least compression).
2. Examine the resulting file in a file manager. I just tried one with these dimensions, exporting from Lightroom, and the resulting file was much smaller than 3 MB. However, for reasons people have noted, the size will vary.
3. If it is over 3 MB, then repeat the process with modestly lower quality (greater compression).

[miatab]

Thank you for all your help and knowledge. I think I was unclear in my post, in my ignorance. What I should have said is that my results after exporting at 1800 X 1200 pixels are disappointingly low- way below 3mb, less than a megabyte, and I have no way of knowing the results of projecting a less than 1 mb file for viewing/exhibition. 2.5 mb would be super, but I am not getting near that.This low number result is after importing from camera to Apple Photos as a 8 to 9 mb jpeg image and doing no editing except resizing. What am I doing wrong?

[DanK]

Thank you for all your help and knowledge. I think I was unclear in my post, in my ignorance. What I should have said is that my results after exporting at 1800 X 1200 pixels are disappointingly low- way below 3mb, less than a megabyte, and I have no way of knowing the results of projecting a less than 1 mb file for viewing/exhibition. 2.5 mb would be super, but I am not getting near that.This low number result is after importing from camera to Apple Photos as a 8 to 9 mb jpeg image and doing no editing except resizing. What am I doing wrong?

Again, I don't know your software, but I would guess that you are selecting too high a level of compression (too low a quality level). the more you compress, the smaller the size and the lower the quality. This doesn't have much impact at the low-compression end, but at the high-compression end, it does.

[Black Pearl]

You're not doing anything wrong.

1800x1200 is only around 2 million pixels so that will produce a smaller file than your original.

[dje]

Yes Ken I mis-understood your question. You aren't doing anything wrong. It's quite normal to get file sizes less than a MB for an 1800x1200 image, depending on the quality setting you use. Even with the maximum quality setting for the jpeg compression on a busy image, you will usually still get way less than 3MB.


Dave

[miatab]

Thanks all; I'm sure the solution to my problem is here in one or more of your comments, and I'll report back when I've tried your ideas. Been and am still ultra busy with granddaughter, a leaking hot water tank and heavy rains, flooded driveway, in the nastiest October I can remember ; Goldener Oktober where have you gone? Autumn images will be rather wet, bedraggled, and the only colour is the apple tree, still not picked. How I long for the surf and sand of my youth in AUS.