1/ Eight levels — Whereas the Levels adjustment in Photoshop has just three sliders, Photos has eight. This gives you precise control over the brightness levels of all the tones in an image. For example, you can control brightness levels in just the darkest shadows, or just the midtones, or just the lightest highlights, plus in the tones that fall between shadows and midtones, and in the tones that fall between midtones and highlights.
The secret lies in turning the feature on (and this also holds true for Histogram adjustment, below): select an image by double-clicking on it, and then click Edit at top right. Now find the adjust button on the right (it’s the fifth down, between Filters and Retouch) and click that.
Now, click ‘Add’ – it’s in blue near top right. Under Advanced, choose Levels… This gives you awesome control over different spectrums of your images.
2/ Histogram — You can adjust the RGB histogram, which shows where image data falls in the red, green, and blue graphs superimposed atop each other – or each colour channel’s individual histogram. You can also adjust the luminance channel, which produces a histogram based on how our eyes perceive colour. This hidden talent lies just under that little three-line-and-dot icon the right of the ‘Auto’ button (above).
3/ Add text to any slide in a slideshow project — Activate a slide in a saved slideshow project and click the plus symbol at lower right of the Photos window (not shown). From the resulting menu, choose Add Text. Highlight the placeholder text that appears and enter whatever you want.
You can’t change the position of the text, but you can change fonts, size, and text colour using OS X’s Fonts panel.
4/ Add a custom vignette — You can apply a customisable dark edge vignette to any picture: open an image in Edit mode and then click Adjust (there’s a shortcut for this, BTW — just press the A key on your keyboard).
Now click the Add button at upper right and from the resulting menu, choose Vignette. Use the Radius slider to change the size of the vignette or rather(you may have to activate this by clicking the Disclosure Triangle that appears to the right of the Auto button when you put your cursor there).
Drag the control right to make the vignette bigger or left to make it smaller. Use the Softness slider to control the width of the transition area between what is darkened and what isn’t. Drag it right to increase the feather effect, thereby making the transition wider and softer. Click the blue circle with a white checkmark to toggle the vignette off and on to see a before and after.
5/ Customise Book pages — Have you noticed you can build books in Photos just like you could in iPhoto? It’s under the File menu>Create Book.
Happily, you can change page layouts, swap pictures between pages, and add pictures to pages while you’re viewing all the page thumbnails in a book project. In other words, you don’t have to double-click a page to do it.
This results in a much broader view of the overall book project than you ever had in iPhoto because you can still see all the pages while you’re designing the layout. To swap pictures between pages, click and hold your mouse button until the picture on the page sprouts a blue border, and then drag it atop an image on another page. To move the pages themselves, click to activate them and then drag the handle that appears underneath them.
[These tips came from Macworld, where you’ll find an extra tip.]