I am looking for PSD files viewer. Gimp is too fat for this job. I need something fast and light.
Ubuntu – Fast PSD files preview
software-recommendation
Related Solutions
GPicView
I'll recommend to you this Simple and Fast image viewer.
As you say that you computer is not a super fast calculator you should look for software with a few functions (the fewest possible), and this software meets this requirement, see the next screen-shoot and you will notice it.
You can install it through the Software-Center.
Dolphin has this exact feature, and with a lot of options. The size of the preview can be adjusted quickly simply by adjusting the width of the side panel, showing as much as the entire first page. Depending on the configuration, it can also preview music/video files.
Best Answer
You may like Kuickshow.
"KuickShow is an image browser/viewer with a nice filebrowser to select images to be shown, slideshow support and the ability to display the following image formats: jpg, gif, tiff, png, bmp, psd, xpm, xbm, pbm and eim. Images can be displayed either in their own window, as large as the image, or fullscreen (which shrinks images too large to display). KuickShow also has a slideshow mode."