In Photoshop and most other main editing platforms there is a Threshold filter.
Threshold Workflow 1. Open Pixlr E 2. Open image 3. SelectAdjustment - Threshold 4. Use the slider to adjust for more black or more white - depending on the image
Curves workflow 1. Open Pixlr E 2. Open image 3. SelectAdjustment - Curves 4. Double click on the Curves line 1/3 along from the bottom and drag the line down until it touches the bottom of the graph - pull it along to the centre line 5. Repeat this at the top of the Curve line 6. Adjust the image by moving both lines left or right
Selective Colour using Pixlr X
Selective Colour is a fun technique. You will have seen images created using this technique before.
1. Open Pixlr X with the link above 2. Open image 3. Click the 3 dots on the image below the layers headline to the right of your screen 4. Choose Duplicate layer (two images overlayed symbol ) 5. Chose Adjust & Filter ( The two sliders symbol) 6. Choose B&W 7. Choose CUTOUT (the scissors symbol) 8. Select the DRAW CUTOUT tool 9. Select brush size (depending on image to be coloured ) 10. Select 25% Softeness 11. Recolour the image - adjusting brush size at the edges If you need to correct change the cutout mode from REMOVE to KEEP 12. Save image - remembering to change the name