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What are thumbnails?

QuickSlideshow can create files consisting of small copies of your pictures, which are displayed on the screen at about the size of your thumbnail (hence the name). These are used to quickly view a collection of pictures, change the order in which pictures are displayed, add new pictures, and remove existing ones.

Thumbnails are intended for small to medium-size collections of pictures (up to a few hundred). Very large collections of pictures may exceed the memory capacity of your Mac. See the section "Memory usage", further on in this document, for more details.

Thumbnails example

Getting started

Opening an existing thumbnail file

If you already have a thumbnail file, just open it from within QuickSlideshow by using the "Open" command under the Thumbnail menu, or double-clicking on it in the Finder.

Creating a new thumbnail file

To create a thumbnail window, use the "New" command under the "Thumbnail" menu which will create a blank thumbnail window. Then add files one at a time by choosing "Add file", or a folder full of files by choosing "Add folder". To add a folder full of files, just choose any file in the desired folder. All files in that folder, and all folders below it, will be added to the thumbnail window.

As pictures are added to the thumbnail window you will see boxes appear on the screen, one for each picture, with the file sequence number (starting at 1) and the file name, inside each box. Then QuickSlideshow will "populate" the thumbnails by reading the images from disk, decoding them, shrinking them, and drawing them inside the boxes. This occurs at a rate of about 1 per second. While pictures are being loaded you can use QuickSlideshow to do other things, such as starting a slideshow, or re-arranging the order of pictures, however response to the mouse and keyboard will be a bit sluggish, due to the disk and CPU overhead of loading thumbnails.

Thumbnails preferences

Viewing the slideshow

When a thumbnail window is open, just press "return" or "enter" and a slideshow will start, displaying all selected thumbnails, or all thumbnails if none are selected. You can also choose "Slideshow" from the "Thumbnails" menu to start the slideshow.

Stopping the slideshow

To stop the slideshow and return to the thumbnail window, just press "Esc" or "Command-period".

Adding more pictures to a thumbnail window

You can add further pictures to the thumbnail window at any time by choosing "Add file" or "Add folder" from the "Thumbnails" window. New pictures are always added to the end of any existing ones.

Removing pictures from the thumbnail window

Simply select the pictures to be removed (by clicking on them, see below for more details about selecting pictures), and then press the "Delete" key, or choose "Clear" from the Edit menu.

Selecting pictures

QuickSlideshow provides various options for selecting pictures in a thumbnail window. Selected pictures can be copied, moved, displayed or deleted.

Selected pictures are displayed with a thin cyan (blue) border. Also, if the picture does not exactly fit into the thumbnail area, the "blank" part of the picture will also be cyan, rather than grey as for unselected pictures.

To select one picture

Click with the mouse on any picture to select it.

To select a range of pictures

Click with the mouse on the first picture in the range, and then hold down the Shift key and click on the last picture in the range. All pictures in that range will be selected.

To select non-continuous pictures

Hold down the "Command" key and click on pictures. As you click on each one it will be added to the selection. If you command-click on a picture that is already selected, it will be deselected.

To select a picture by name

Choose "Find picture by name" from the "Slideshow" menu. Type in enough of the name to uniquely identify the picture you are looking for (e.g. "cat" would find the picture "Pussy cat"). If a match is found, the matching thumbnail is selected, all other thumbnails are de-selected, and the window scrolls if necessary to show the selected thumbnail.

To select a picture by number

Choose "Go to picture number" from the "Slideshow" menu. Type in the desired picture number (the allowable range is shown in the dialog box), and then the appropriate thumbnail is selected, all other thumbnails are de-selected, and the window scrolls if necessary to show the selected thumbnail.

To de-select pictures

Hold down the "Command" key and click on previously selected pictures to de-select them.

To select all pictures

Choose "Select all" from the Edit menu.

To deselect all pictures

Choose "Select none" from the Edit menu.

To invert the selection

Choose "Select inverse" from the Edit menu.

Inverting the selection means that all pictures which were not selected become selected, and all selected pictures are deselected. This is useful on occasions such as when you want to copy, say, all but 10 pictures to another window. It is quicker to select the 10 pictures that you don't want, and then invert the selection, than to select all the pictures that you do want.

Saving thumbnails to disk

Choose "Save" from the Thumbnails menu to save your thumbnail window to disk. Choose "Save as" if you want to save them under a different name.

Re-arranging the order of thumbnails

You can re-order your slideshow by simply selecting thumbnails by clicking on them (see above for more details about selecting thumbnails) and then simply dragging them with the mouse to a new location.

When the mouse is over a valid destination, that is over another thumbnail, or over an empty thumbnail window, the mouse pointer changes to a distinctive shape indicating that you may let go of the mouse button, and the selected thumbnails will be moved to after the thumbnail under the mouse. If the mouse is not over a valid destination the cursor will appear as a "stop sign".

Moving thumbnails

The default behaviour when dragging selected thumbnails with the mouse is to move them, not copy them. When moving thumbnails they are removed from their original location, and moved to the new location.

Copying thumbnails

If you want to make a copy of the selected thumbnails, hold down the option key after you start dragging the selected thumbnails. The mouse pointer will change slightly so that it has a "+" sign as part of it. This is your visual confirmation that you are making a copy. You must leave the option key held down until you release the mouse, or you will move them thumbnails, not copy them.

Moving the selected thumbnails to BEFORE the one you are pointing to

If you want to move or copy the selected thumbnails to before (in front of) the one you have dragged them to, hold down the shift key after you start dragging the thumbnails. The mouse pointer will change slightly so that it has a "left-pointing arrow" as part of it. This is your visual confirmation that you are making to the left of the thumbnail the mouse is over. You must leave the shift key held down until you release the mouse. This is particularly useful for moving the selected pictures to the start of the window.

Dragging to a location that is not currently visible

If the destination thumbnail that you are dragging to is not visible, the window will scroll vertically if you move the mouse to just above, or just below, the edge of the thumbnail window.

Moving or copying thumbnails to another window

You can copy or move thumbnails, as described above, to another thumbnail window. This is useful for, say, opening a thumbnail file with a large collection of pictures, and then dragging selected ones to a new window so that a subset of the original collection is used for a new slideshow.

Viewing individual pictures from the thumbnail window

After selecting one or more pictures by clicking on them, just press "return" or "enter" and the selected pictures will be displayed as a slideshow. Press "Esc" or "Command-period" to stop the slideshow.

Alternatively, you can double-click on a thumbnail to view it. If it is part of a group of selected thumbnails all of the selected ones will be displayed.

Thumbnail viewing options

By choosing "Preferences" from the Thumbnail menu, you can change the size of the thumbnails, and control whether or not:

Note that the larger the thumbnails are the easier they will be to see, but the more disk and memory space they will take up. A 50 X 50 pixel thumbnail file needs 5,300 bytes (5 K) per picture. A 100 X 100 pixel thumbnail files needs 20,300 bytes (20 K) per picture. See "Memory usage" below for more details.

If you resize your thumbnails (by changing the width or height of the images) you should consider reloading any existing images. To do this, choose "Reload" from the Thumbnails menu. Until you do this, any existing thumbnails are stored using the dimensions that you chose when those pictures were loaded. If the current thumbnail size is different from that, then the images are scaled to fit the new dimensions.

If you have gone from smaller images to larger ones, then the old images may look "chunky" as they are scaled. If you have gone from larger images to smaller ones, then although the images may look alright, they will be taking more memory than is now needed to hold them.

Reloading thumbnails

The command "Reload" under the Thumbnails menu removes all thumbnail picture data from memory for the selected thumbnails (or from all thumbnails if none are selected), forcing the thumbnail images to be reloaded from disk. You should do this after changing the size of thumbnails, so that the pictures are reloaded with optimal picture quality and memory usage.

Sorting thumbnails

The command "Sort" under the Thumbnails menu sorts all thumbnails into alphabetic order by filename.

Converting thumbnails to a tag file

If you wish to save disk or memory space you can save your thumbnails as a "Tag file". This is a file that QuickSlideshow can open to show the selected pictures as a slideshow, however the thumbnail picture data (small images) are not saved. Tag files use substantially less disk and memory space than thumbnails. As a guide, a tag file needs about 40 bytes per picture, but a 50 by 50 pixel thumbnail file needs about 5,300 bytes per picture.

You may wish to use a thumbnail window to select and arrange your pictures, but save it as a tag file once the pictures are in the correct order.

If you double-click on a tag file in the FInder then the appropriate slideshow commences after a short delay. You can also open a tag file by using the "Open" command under the File menu.

Tag files can be converted back into thumbnail files as described below.

Converting tag files to thumbnail files

To convert a tag file into a thumbnail file:

The pictures contained in the tag file will be displayed in the thumbnail window. It will take about one second per picture to reload the images from the original files.

Memory usage

Keeping thumbnail pictures in memory takes quite a bit of memory per picture. The exact amount depends on the size of thumbnails that you select, using the "Preferences" command under the Thumbnail menu.

Memory for thumbnails

The approprimate amount of memory needed for holding thumbnails is:

((width * height * 2) + 300) * number-of-thumbnails

For example, if you have 200 thumbnails at 64 X 48 pixels, you will require:

((64 * 48 * 2) + 300) * 200 = 1,288,800 bytes (1.2 Megabytes)

The thumbnail file on disk takes up the same amount of space, plus a couple of hundred bytes for the "file header".

Memory needed for doing a slideshow

In addition to the memory needed for holding the thumbnails in memory, QuickSlideshow needs enough room to hold:

Total memory requirements

Based on the above figures, allocating about 2.5 Mb to QuickSlideshow would let you work with 200 thumbnails, of size 64 X 48 pixels.

Of course, if you wanted to have a second thumbnail window open consisting of another 200 thumbnails, you would need another 1.2 Mb (total of 3.5 Mb) and so on.

Allocating more memory to QuickSlideshow

To allocate more memory to QuickSlideshow, use the "Get Info" command under the File menu in the Finder to open an information window about QuickSlideshow. Then change the Minimum Size to the desired figure. For example, to allocate 3.5 Mb enter 3500 K bytes.

Thumbnails drawn with a blank red box

If there is insufficient memory to load a thumbnail picture, the thumbnail box will be displayed in red rather than grey, to indicate a low memory situation.

How to cope with low memory

First, if you are short of memory, choose a small size for your thumbnails. Even thumbnails as small as 40 X 40 pixels are reasonably easy to view, provided you have your monitor set to thousands or millions of colours. The amount of memory needed for thumbnail images increases in proportion to the square of the picture size, so doubling the size of your thumbnails increases memory requirements by four times.

If you still don't have enough memory to hold your entire slideshow as thumbnails, consider breaking it up into smaller thumbnail files, each containing a logical portion of the slideshow. Then just work on one thumbnail window at a time (closing the ones which are not in use).

You can then save each one as a tag file (which uses a lot less memory), and then combine them by selecting the tag files in the Finder (as a group) and dragging and dropping them onto the QuickSlideshow icon. Having done that you can then save the resulting slide show as a single tag file. Note that the order in which the tag files are processed (displayed) is the same order that you click on them in the Finder.

Optimum number of colours to set your monitor to

The thumbnail images are held as 16-bit RGB images (this is the same as "Thousands of colours" in the Monitors control panel). This image style was chosen because it is the most appropriate for holding many pictures which may use different colour palettes.

For optimal viewing therefore, your monitor should be set to "thousands of colours".

You can use "millions of colours" if you wish, however the images will not be shown an better, and the refresh rate of the screen is slower, due to the Mac having to move more data into its screen buffers.

If you use "256 colours" then the thumbnails will be "dithered" which means that they will still be legible, but not as clear as if you use "thousands" or "millions" of colours.

If you use less than 256 colours, both the thumbnails and the slideshows will be significantly degraded in colour quality.

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Written by Nick Gammon - 5K

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Page updated on Wednesday, 15 December 2004