Image Size Reduction

[Chris M]

When reducing the size of an image from, say 20,000px x 10,000px, to 1000 x 500, is there a quality difference between typing the sizes in the Width and Height on the toolbar vs its toolbar neighbour Scale By Percentage?

[handrawn]

never noticed a quality difference chris, although I use mostly PNG not JPG

[Acorn]

@Chris, there ought not to be.
Xara keeps its images unpacked and only applies compression when rendering or exporting.

Acorn

[handrawn]

@acorn you are more technical than I am

my understanding is that the render you see in the workspace is not the image itself - altering the view quality being the most obvious example - there may be small rounding issues with the workspace render, and these may differ between the methods, and JPG artifacts may play a part... but non of this affects the actual image [what you said effectively ?]

[Acorn]

@acorn you are more technical than I am
my understanding is that the render you see in the workspace is not the image itself - altering the view quality being the most obvious example - there may be small rounding issues with the workspace render, and these may differ between the methods, and JPG artifacts may play a part... but non of this affects the actual image [what you said effectively ?]

@handrawn, more or less.
Inputting an actual size or a percentage will only be affecting the numeric calculation not the render.

@Chris - try this.

Size and scale to create two "identical" images.
In the Bitmap gallery, right-click each image and in its Image Properties: Untick Smooth when scaled up.
Now Zoom in and you will now see individual pixels unsmoothed.

Easier to make a value judgement.

Acorn

[Chris M]

Thank you both. This started with a friend casually talking about reducing images for emailing. He made the comment that reducing by percentage retained the quality of a photo, whereas picking a pre-determined size from the options didn't. He was talking about mobile phones, but it had me wondering.