# Is possible to reduce the brightness from specific object?

Hello guys! I’m newbe on ImageJ, so I gratefull for any help.

I need the perimeter, area and area fraction from this white panel.
So I do it: 1º Straight
Analyze>Set Scale
Poliygon
Edit>Clear outside
5º _Analyze>Set measuramentes>pick up_perimeter, area and fraction area
Image>Type>8bit
Image>Ajust>Threshold
Analyze>Mesuare

But after Threshold some parts of objects in front of panel came white. I want, after Threshold, that just panel stay white and all other objects stay black, How can I do it?

I alredy tried Convert to mask, Fill hole, Watershed and manually Fill it.

Ty

Hello, and welcome!

You can get better suggestions if you can explain more exactly what you mean by perimeter, area, and area fraction.

• Do you want the perimeter of the whole rectangular panel? Or some other measurement? (can you draw an outline on the image to illustrate?)
• Do you want the whole area of the panel, or the area that is not covered by trees?
• How is area fraction defined?

Hope this helps for a start.

2 Likes

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Thank you for help tswayne. I’m going to be more specifically.

On above image I used these steps:
1º Straight (from beginin to the end of painel)
2º Analyze>Set Scale (3 meter)
3º Poliygon
4º Edit>Clear outside
5º Analyze>Set measuramentes>pick up_perimeter, area and fraction area_
6º Image>Type>8bit
7º Image>Ajust>Threshold
8º Analyze>Mesuare
and got this image

The problem with it is I don’t want any part of these trees came black, just the panel have to came black.

So, with the trees complete white and panel complete black the result I want is the percentual of the black area in Polygonon.

Try the Color Threshold. This should allow you to distinguish the white panel from the light patches on the tree.
To do this, omit step 6 and run Image > Adjust > Color Threshold on the RGB image.

Is this Edit > Selection > Straighten? It seems unnecessary.

You don’t have to do this because the measurement will automatically be restricted to the polygon you draw.