Pasting Into An Alpha Channel

[WG48]

I downloaded a trial version of Affinity to see how it compares to Photoshop CC.  

I learned a technique for removing blue tarnish on old photos in a book by Ctein (Digital Restoration From Start To Finish - an excellent resource for those who are serious about restoring old faded and damaged photos) by exagerating color to select tarnish and create a mask to remove the tarnish.  The technique involves using HSL & Channel Mixer to create a grayscale mask.  When I try this technique in Affinity, I encounter a problem in Channel Mixer.  In PS, the channel mixer has a monochrome check box that makes the output channel gray but keeps the RGB sliders for adjustment (see screen shot below).  In Affinity when I make the output channel gray, the RGB sliders go away and are replace with 3 different sliders - intensity, alpha & offset.  I played with these adjustments to get an image like the one I had in PS.  I then converted the image to grayscale and saved it.

In PS I then open the original image and paste the grayscale image/mask into an alpha channel.  Next I do a curves adjustment to remove the tarnish and then go back to RGB to see the finished photo without the tarnish.  When I tried this in Affinity, it kept pasting the grayscale image as a new layer rather than into the alpha channel.  How can I paste the grayscale image into an alpha channel?

Below are the original photo, the HSL adjustment to exagerate the color and the PS channel mixer adjustment.

 

[Dan C]

Hi @WG48,

Sorry to hear you're having trouble! could you possibly provide a copy of your .afphoto file, up to the point where you need to paste into the Alpha channel - so that I can provide some specific advice for you?

Many thanks  

[WG48]

Thanks for your offer to help.  My trial version of Affinity expired yesterday.  Haven't bought the full version yet.  Will get back to you if I do.

Basically I was trying to follow the procedure I used in Photoshop CC.  I ran into problems in step 5 and never could move on steps 6 & 7.  Below is how to do the technique in Photoshop CC

Making Specialized Masks From Colors In PS CC

1.     You can exaggerate colors to select tarnish on a photo by making a Hue/Saturation adjustment of +70 or more. 

2       Next look at the channels to see which one shows the damage best.  Then use Channel Mixer on the RGB channel to subtract the cleanest channel from the most damaged channel.  You do this by                        checking the monochrome box and then cranking up the dirty  channel to 200 and bring down the clean channel to -155 or more. 

3      Once you get a good mask, convert it to Grayscale (menu bar – Image, Mode, Grayscale and choose Flatten image).  Save the image.

4      Open the original image again and the grayscale image.  On the grayscale image, select all and copy.

5      Select the original image and add an alpha channel.  Click on the alpha channel, select all and then paste the mask into the alpha channel.

6       Go back to the layers panel & click on the image layer.  Go to menu bar – Select, Load Selection.  Choose the alpha channel and check the invert box.

7       Next add a Curves adjustment layer and use the eye dropper to click in the photo where the tarnish is (hold Shft & Alt key down to place a point on all three channels).  Adjust each channel to darken and              get rid of the tarnish.

[kirkt]

@WG48 - In AP, you can emulate the effect of the monochrome checkbox that is in PS by:

0) - It looks like you added a HSL adjustment (A in the attached screenshot) to accentuate the blue of the tarnish.

1) Add a Channel Mixer adjustment layer (B) to the stack (this is where you will accentuate the tarnish by manipulating the R, G and B content in each channel)

2) The effects of the Channel Mixer (D) can be seen in monochrome by viewing just the targeted channel of the composite image.  In this case, the blue area will be WHITE in the mask you ultimately want to create, and the rest of the image should be BLACK or dark, to avoid being affected by whatever adjustment you make.  In other words, the adjustment you ultimately make will target the blue area in the image, which has been intensified by the HSL boost in step 0.

In the Channels panel (C), click on the blue composite channel thumbnail to view just the blue channel, in grayscale.  In the Channel Mixer adjustment, select the blue channel (D) and push the blue (dirty) channel slider up to 200% and the red (clean) channel down to 200% or so.  The composite blue channel should look a lot like the mask you posted in the screenshot of the PS result.

You can right-click on the blue channel and create a "Spare Channel" from the blue channel - this will be your mask (E - I renamed the Spare Channel "BLUEMASK").

 

Kirk

[kirkt]

Here is a screenshot of the resulting Spare Channel (BLUEMASK) applied to a HSL adjustment to target the blue in the tarnish and shift its Hue to the sepia of the rest of the photo.  To apply the BLUEMASK spare channel to the HSL adjustment layer, add the HSL layer and make sure it is the active layer.  Then right-click on the BLUEMASK spare channel in the Channel palette and select "Load to HSL Shift adjustment Alpha" - this will load your spare channel to the inherent mask of the HSL adjustment layer.

I would think there are other adjustments to contrast, etc., that will need to be made to combat the effects of the tarnish, but you get the idea.  Because these other adjustments probably also involve the exact same area as the blue, you can reuse the mask to target the same area.

Have fun!

Kirk

[kirkt]

Here is a split (upper left to lower right) before and after.

Kirk