Hi Hilda and welcome to RetouchPRO.
Your first go was quite ambitious! I recommend you start with smaller, less intricate images with a single subject and work your way up to multiple subjects as you gain experience.
Your second image is a good example with which to start.
Check out
this tutorial. It's considered by many to be the best method for colorizing B&W photos.
However, I prefer colorizing in LAB and painting directly into the A&B channels.
Go to Image>Mode>LAB Color
Paint directly into the A & B channels. Use a soft brush with a VERY low opacity and flow (10% or so) until you get a feel for what you're doing.
To begin:
Hit the D key to get the default colors.
Open the Channels palette. This step is optional. Display the palette only to keep track of which channel is being worked on. Once you're confident with the technique displaying the channels palette is not necessary.
Use Cmd/Ctrl 2 to select the A channel. This channel affects green-magenta.
Use Cmd/Ctrl 3 to select the B channel. This channel affects blue-yellow.
After selecting a channel hit the tilde ~ key to view the composite image so you can see the changes.
Painting with black on the A channel will send the pixels towards green, white will make them magenta.
Painting with black on the B channel will send the pixels towards blue, white will make them yellow.
Black in both the A & B channels will create cyan, white will create red. However, you can't paint in both channels at the same time.
50% gray in both channels is neutral, no color at all. These are your whites, greys, and blacks. This is what your A & B channels will look like at first.
To remove color or erase mistakes paint with 50% gray.
With all this painting you will never harm detail.
Your A & B channels should end up being very subtle, blurry shades of grey. To help get an idea of what the A & B channels should look like when you're done, open a color image which is similar to your working image and convert it to LAB. Then view its A & B channels.
As a final step you should convert the image to RGB (Image>Mode>RGB).
This can be a very fast and painterly technique. Once you get the hang of it the actual mechanics boil down to changing brush size and opacity, hitting the X key to swap black & white, and switching channels to target colors.
Here's a
before and
after which I did using this technique.
Let me know if you try it and what you think.
Here are my thoughts on your second image:
The first thing I noticed is the extremely harsh edges throughout. Colorizing is very much about transitions and attention to detail. Your masking is much too obvious.
One solution to soften transitions is to use a slight Gaussian Blur on your masks followed by a Levels adjustment to fine tune.
Also notice the hair around the forehead. You've painted the skin tone onto the hair. And the area under the subject's right forearm not only doesn't follow the arm but also spills onto the desk. This is why attention to detail is so important.
I think replacing the background is a mistake. There's quite a bit of detail back there, such as the wainscoting, which adds to the charm of the picture. It also makes the subject look like she was cutout and pasted on like a Monty Python cartoon.
I hope my comments don't appear too harsh, but this is the Critique room.
If you have any questions about the LAB technique don't hesitate to ask.
Good luck,
Michael