Multiband imagery - tool problems image calibration and merging

[Patina70]

Hi, 

I am working in multiband imagery for art identification. Until now, I always used Photoshop, but would very much prefer to change to Affinity. However, I already struggle with the first steps of image calibration :

A calibration chart is included in the image to edit the image later and minimize color deviation (see picture, first all three steps in photoshop, then in affinity)

1. In "Levels", the darkest and the lightest plot are then calibrated in a first step in each channel, the dark one is fixed on 42 and the light one on 249 in each channel. However, although color info shows the numbers, levels shows percentage and I cannot find a way to make levels show the RGB numbers.

2. Next step would be to fix every chart plot in a definite number in each channel in "curves". But here, I only get numbers between 0 and 1 (or 0 to 100, if I change the max outcome) and not between 0 and 249

3. Finally, in "channels", I would create a false color image by selecting a channel and replacing it with another image (e.g. an infrared or UV-reflection). Although I have figured out how to show the channel window, I don't seem to be able to separate them, in order to erase or copy or distort them in only one layer.

 

I don't know if my request is clear enough, but I really need help. I really like Affinity and I only start with it. I think it has so much more potential, but if I can't figure this out, it is more or less useless for me.

Best regards

 

Janin

[NotMyFault]

1 hour ago, Patina70 said:

1. In "Levels", the darkest and the lightest plot are then calibrated in a first step in each channel, the dark one is fixed on 42 and the light one on 249 in each channel. However, although color info shows the numbers, levels shows percentage and I cannot find a way to make levels show the RGB numbers.

Hi Janin,

welcome to the forum. I don't use PS, so I may misinterpret your sentence. Do you want the color of the almost black circle (on the right) to be 42? Simple math gives you 42/255 is about 16%, or rounded 0.16, and 249/255=97,6% or 0.98. so black should output 0.16, and white should output 0.98?

Instead of using the levels adjustment, maybe the curves adjustment allows better 2 digit numeric control. 

add a curves adjustment. Then activate the "picker" in that curves adjustment by clicking it once, and the click on the canvas on the "black" pixel reference area.

A node is added to the curve. Click on that node, then you can use numeric input for "y" value to assign the number 0.16

Do the same for the white point. Ignore the curvature for a second. When both nodes are ready, drag the end nodes (at x=0 / xx=1) so that the curve becomes a straight line again. Unfortunately, only the iPad version has the UI element to use "linear" lines between nodes. I will upload a file with such an adjustment layer, you can copy it into your documents to make this workflow simpler.

linear curve.afdesign

[NotMyFault]

1 hour ago, Patina70 said:

3. Finally, in "channels", I would create a false color image by selecting a channel and replacing it with another image (e.g. an infrared or UV-reflection). Although I have figured out how to show the channel window, I don't seem to be able to separate them, in order to erase or copy or distort them in only one layer.

 

The channels panel requires a steep learning curve, as its UI is not very intuitive.

An easy approach is go one step indirect via "spare channels". if you want to copy a channel, open/select the source pixel layer, and right-click on the designated channel (R,G,B) and click "create spare channel".

Then go to the destination layer and activate it in the layers stack. It must be of type "pixel layer". If it is a image layer, use "rasterise" to convert.

Go to the channels panel again, select the "spare channel" you created before. right click, and select "load to pixel red" or the designated channel you want.

[Patina70]

Hallo nach Hamburg,

first of all thank you so much for such a quick answer. I will try that out and come back to you. But I can already tell you that the picker does not make nodes on the curve. 

Apart from that, you are right that I don't need to do it with the 249 numbers!

Greetings from Paris

[NotMyFault]

I have optimised the workflow for you. please find the file attached.

It contains my asset library (make it visible via view->studio->asset if not visible).

so the basic steps are:

1. open the file in Photo
2. drag the "neutral linear curve RGB" asset as layer atop the image
3. use the info panel. Select the first picker. set mode to "crosshair". drag the crosshair to the black reference color area in the document
4. Select the second picker. set color mode to "RGB" via the small burger menu visible when clicking on the small symbol with 3 circles. set mode to "crosshair". drag the crosshair to the black reference color area in the document
5. double-click the curves adjustment layer
6. select the red channel.
7. click the "picker" once
8. in the canvas, on the black reference color area, click and drag upwards. This creates a node. (clicking without dragging does not work)
9. click on the newly created node to select it
10. now click into the "Y" numeric field. adjust the value (e.g. by mouse school wheel) and inspect the black color picker, until it shows the desired value (e.g. 19) +/- 2 (so 17 to 21 would be ok, you can't always match it perfectly)
11. ---> repeat this process for the white reference color (from step 😎
12. delete the superfluous node in the exact middle (0.5 / 0.5)
13.  ------->  repeat the process for green channel from step 6
14.  ------->  repeat the process for blue channel from step 6

As result, you get a perfect calibration of the image to the desired values of black / white reference colors.

color matching with linear curve.afphoto