Magic Wand why when you have tolerance set to 0 with antialias off it selects other colours

[mardymarvin]

I wanted to select only black in the scanned drawing by using the magic wand so set the tolerance to 0% and continous with antialias off, then clicking on the black pixel / line it seems to select other colours so from black to grey.

what do I need to do to make it only select black

[Lisbon]

Hi @mardymarvin

I use A.Photo v1 but I think that won't be a problem.

2 hours ago, mardymarvin said:

...by using the magic wand...

I assume you are referring to the Flood Select Tool [W], right?

2 hours ago, mardymarvin said:

...it seems to select other colours...

Since in your example the pixels have very different opacities, we can be led to think that gray tones are being selected.

The only way to be sure is to open the info panel and measure some pixels.

As you mentioned, with the tolerance set to 0%, all selected RGB values must be the same. In the case of black RGB = 0 0 0

If they are different then we may have a problem.

2 hours ago, mardymarvin said:

what do I need to do to make it only select black

Is it possible that you are trying to select fully opaque black pixels?

[mardymarvin]

hi Lisbon

Thanks for the reply I will be honest I have no idea what you mean by opaque black I just thought if black was more opaque then it went more towards grey but very ignorant in this concept. However I have followed your instructions and used the eyedropper on what I thought were see through not black pixels so in my mind should not have been select but they came back as black in RGB 0,0,0 like you said and so do all the gradients of grey.

It looks like its becuase I have used the Filters > Colours > Remove White Paper and then using the Flood Select Tool. If I dont use the filter then it works as I expect so I assume the filter is doing something strange (well to me) and not a simple if its white delete it. I assume this is where it creates opaque black which would mean the flood fill sees it as the same but my human eye does not. It confused me more when I select another pixel that looked the same to me next to the opaque black and that was not opaque black. Just picking my brain up off the floor now after the explosion.

So I think I will just not use the filter as I dont understand what its actually doing.

I tried reading a few sites about opaque black and other colours and it at the moment it is above me but I am very happy you replied as at least now I know why it was selecting them and that the tool was correct to select them. Every day is a school day

[walt.farrell]

Just as an example, here are two rectangles, both are RGB 0/0/0 Black. The top one is 100% Opacity, the bottom one is 50% Opacity. The Flood Select Tool considers them the same color because it is using the RGB values which are the same.

[Lisbon]

Note that in the info panel we have the RGB information and also "A" (Alpha). If a pixel is fully opaque A=255. If a pixel is 50% opaque then A=127. And so on.

[MEB]

Hi @mardymarvin,
Welcome to Affinity Forums
Try menu Select > Alpha Range > Select Opaque to pick up just the solid black pixels.