Photoshop does not wat to edit a scanned drawing

[ilka_2793]

When I try to make adjustments to a pencil drawing in photoshop, for example reducing brightness or contrast, the adjustment is shown in preview, but when clicking 'OK', no changes are made. I only have this problem on a MacBook air and not o

When I make the same adjustments on a photograph, this problem does not occur.

How can I solve this?

[Myra Ferguson]

Would you mind posting a screenshot that includes your full screen or a video demonstrating the issue?

[ilka_2793]

Hello Myra,

See short video attached.

[davescm]

Can you try the same adjustments with the preview at 100% zoom? 

Dave

[ilka_2793]

Hi Dave

When I try to make this adjustment at 100% zoom, noting is happening at all.

[davescm]

The 100% preview, which maps 1 image pixel to 1 screen pixel, is showing the real impact of the adjustment.

If your image is made up of black pixels and white pixels, as might be the case with a scanned line drawing, there is no grey to adjust, so the adjustments you used can have no effect. It can't darken an already black pixel or lighten an already white pixel.

When you zoom out several image pixels are combined together for the preview. So adjacent black and white pixels take on a grey value in the preview. The image adjustment on those grey values can darken or lighten them. However, that is only the preview. When you apply the adjustment it acts on the actual image pixels which, as they are already being black or white, has no effect.

For many images the difference between preview and 100% zoom is minimal. But for images with fine noise ( or fine black and white pixels) the difference can be huge. Always check adjustments at 100% zoom where you are seeing the real effect.

Dave