Compare Documents

If a document exists in two or more versions, it is possible to compare these efficiently in the viewer.

The first step of a comparison is to select the documents to compare and ensure that they are aligned as well as possible. See The File Selection Bar)

When comparing is enabled, an extra row of radio buttons is displayed in top of the Channels panel.

With these buttons, it is possible to select viewing the current version only, the previous version only, or a combination of the two with different degrees of highlight of the differences. The selected view mode will control not only the image view, but also the channels readout in the Channels panel.

Viewing the current version only

Push the current version button to view only the current version of the document. This is the standard display mode where the previous version is not shown at all.

Viewing the previous version only

Push the previous version button to view only the previous version of the document. The displayed channels will change to those present in the previous version. Note that the image dimensions will stay the same as for the current version.

Viewing both the current and the previous version

There are five different view modes for displaying a combination of the current and the previous channels in the same window. Four of these are reached through the view both button . The functionality of this button is set by right-clicking the button itself. The top four menu items selects which of the four modes that should be activated when the view both button is selected.

The first mode is used to simply overlay the two versions. This is typically used when they together form a complete layout e.g. a left and a right page of a reader spread. Or two parts of a package design that is rendered separately, but where some parts have to be aligned to one another. Use the alignment and alignment offset controls in the top panel to set the correct alignment of the two parts. See The File Selection Bar

Comparing two versions of the same document

The three remaining view modes that can be activated through the view both button are all used to compare different versions of the same document. The only difference between these modes is how the parts of the document that is unchanged between the current and the previous mode are displayed. In all three modes, special highlights colors are used for added and removed details respectively.

Select the view both - show differences mode to show the unchanged image parts with normal colors.

Added channels, i.e. channels only present in the current version of the document, is indicated with a trailing "(+)" after the channel name. In the image, the "added" highlight color - here blue - is used to indicate the content of both added channels and added objects on common channels.

Subtracted channels, i.e. channels only present in the previous version of the document, is indicated with a trailing "(-)" after the channel name. In the image, the "subtracted" highlight color - here red - is used to indicate the content of both deleted channels and deleted objects in common channels.

To make it easier to compare the content of channels that does not have the same definition in the two compared versions, it can be a good idea to revert channel definitions to their previous definition. In our example the channel "660" would have to reverted to "661". This is done as described below and results in a changed display where the changed channel only is listed once and only true image changes are highlighted in the image area.

Select the view both - highlight difference mode to show the unchanged image parts with lightened colors making it easier to spot the differences in a colorful image.

Select the view both - only difference mode to show the changed image parts only. Unchanged areas will be white.

This mode is especially useful for spotting small differences in the navigator or when zoomed to view the entire document.

Selecting compare color space

By changing the compare color space, it can become easier to judge the nature of the differences between the compared documents.

To change the compare color space setting, right-click the active view both button , or .

Three options are available:

• Compare: Channels - This is the default mode. Channels are compared one at a time and added/subtracted content is displayed with two solid highlight colors independently of the magnitude of the difference.
• Compare: HSV - Compare colors rather chan channel content. The HSV color of the two documents are compared and the relative difference is shown in a graded color overlay and common parts are shown in a neutral gray color. The overlay color will be a grade of the selected "Subtracted" color with the strength depending of the magnitude of the difference. This will make it easier to compare documents where the channels are not the same e.g. a CMYK document and a document with a combination of Pantone spot color channels.
• Compare: Automatic - With this selection active, Channels will be used as compare color space if the difinition of all the visible channels are the same in the two compared documents. If this is not the case, HSV compare will be used.

In the example below, the two first documents are compared. The third image is the result of Channels mode compare; everything looks changed because the channel definitions are not matching. The last image is the result of HSV mode compare which in this example gives a better view of the changes made.

Viewing both the current and the reference version - blinking

The view both - blinking mode will toggle between the two compared versions. The toggle interval is fixed. It is possible to use other viewer tools like channel selection, zoom and pan while in blinking compare mode.

Press the View both - blinking button to select this view mode.

Viewing two documents side by side

The side by side view mode presents an alternative way of comparing two versions of a document. In this view mode the image display is split in two tiled sub-windows - one for each version. The display in these window will at all times be fully synchronized with respect to channel selection, view position and zoom ratio.

Press the side-by-side button to select this view mode.

By default, the shape of the image view area will determine if the two versions are displayed next to one another or on top of one another (Automatic tiling). If you want to changes this behavior, right-click the side-by-side button and select either horizontal or vertical tiling.

Viewing two documents side by side with difference view

It is also possible to show get the difference view shown next to the two compared versions. To toggle this function on or off, right-click the side-by-side button and select the Show difference view menu item.

When the function is turned on, three rather than two panels are shown. With the compared view on the right (if vertical tiling) or bottom (if horizontal tiling).

The compare mode will be the one last used for comparing two document versions: the View both - show difference, the View both - highlight difference or the View both - only difference mode.

Displaying two documents with one mirrored (recto-verso)

To check from-back alignment of document elements, the recto-verso display mode can be selected.

By default, the previous version of the image will be mirrored horizontally. To change this behavior, right-click the recto-verso button and select the preferred mirroring mode.

Configure difference highlight colors

If the current colors selected for added and deleted image details respectively are difficult to distinguish from the colors present in the current document, it is simple to select different colors that are more suitable.

Right-click one of the three last difference view mode buttons to get a pop-up menu.

To change the highlight color for added details, select the Change "Added" Highlight Color pop-up menu item.

To change the highlight color for deleted details, select the Change "Subtracted" Highlight Color pop-up menu item.

To display both added and deleted details using the same color, select the Change Both Highlight Color pop-up menu item.

To go back to the original colors (blue and red), select the Reset Difference Highlight Colors pop-up menu item.

When the change is made and the dialog is closed, the difference image will be updated using the newly selected color.

Using difference view to inspect changes in dot percentage and pixel count or screen ruling and angle

The readout of dot percentage, pixel count, screen ruling and angle will change depending on the difference view mode selected. If one of the modes that show both versions is selected, the readouts will show differences between the versions if any.

The value in parenthesis will be the value from the previous version. If only one value is displayed, no differences have been measured.

Compare channels with different names or display color definitions

When comparing documents it can sometimes be advantageous to allow channels to be compared directly even if their channel definitions are changed. An example could be if the channel has simply been renamed from say "Blue" to "Pantone 660" as part of the prepress process.

There are two ways of changing which channels are directly compared to which other channels. One is to use the channels edit dialog (see below) to change the channel definition of the current document to match that of the reference document. The easiest way is however to use the channel matching dialog. See The Channel Matching dialog

Alternatively, documents with non-matching channels can be compared using the HSV color space compare (see above).

Use channel edits to compare channels with different names or display color definitions

If one or more channels in a document has been redefined between the two compared versions of the document, it can be relevant to revert the channel definition changes to allow comparison of the image details in these channels.

Note that only channels in the current version can be edited and that the difference view has to be set to view current only for the channel color edit to be enabled.

To make this operation simple, the channel definitions present in the previous version but not in the current can be easily selected from the current color definition drop-down menu in the Channels Color dialog where they are placed below a horizontal divider line. See The Channel Colors dialog

Adjust comparison settings to distinguish between minor and major differences

When comparing images with documents that cannot be perfectly aligned or has minor tonal changes it can de very useful to be able to specify a threshold on when a difference should be highlighted. This can be done with the difference adjustment controls that can enabled from the right-click popup menu on the channels difference view button.

Simply type a percentage value corresponding to the smallest differences value that you want highlighted.

As an alternative, you can also click the little right arrow next to the label use a slider to do the adjustment.

In the Difference adjustment panel, you can also change the color space used for the comparison. The Default is Channels compare.

Keyboard shortcuts

The Ctrl-S shortcut can be used to quickly toggle between the current and the previous version.