# Is possible to reduce the brightness from specific object?

Tags: #<Tag:0x00007fb87cc54f68> #<Tag:0x00007fb87cc54e28>

#1

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

Beginner looking for some guidance
#2

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.

#3

.
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.

#4

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.