Interpreting "Document Size" in PS

It is believed that many PS users have noticed this, but it is not clear exactly what they mean, because none of the instance tutorials will talk about it. Literally, it seems that "document size" should be the size of the file that represents the PSD, but why are there two numbers? and often the actual file size is very different?

First, the thing underneath the document window, like most software, is called the status bar, which, in addition to the document size, displays information about the document configuration, the time spent in the previous operation, and so on. The default setting for PS is to display the document size (documents sizes). In fact, this "document size" is not related to the actual file size.

The left digit indicates the size of uncompressed image data after all layers (flatten) are merged.

Because the image after the flatten, there is no alpha channel, so it is equal to print the file size (printing size), also basically equal to the current document BMP format when the file size

The right number indicates the data size of all uncompressed content (including layers, channels, paths, and so on). To put it another way, it's memory footprint.

For example, a document with only one layer, the left value is 3m, then the right should be 3x (4/3) =4m, because more than one alpha channel, the channel from RGB to Rgba, more than 1/3; then you add a (not blank) layer, then 4x2=8m.

Readers should have found that the common denominator for these 2 values is "uncompressed", and that the PSD is a compressed format in which PS cannot know the actual file size until it is actually stored. The general actual file size is always smaller than the 2 values (unless you add a lot of smart object layers with large size).

Then say "document size" for possible purposes:

Memory footprint Estimate

In the development of some programs or what the time, should have a certain helping role. This is probably the biggest use of "document Size"

Guidelines for storing formats

Said file size, had to say PSB format, this is a PSD format of the delay, size is not limited (PSD can not be greater than 4G, and more than 2G when many third-party programs can not open, PS default (compatibility settings) do not allow you to save 2g above the PSD) and the maximum length and width of the document supports up to 300000 pixels. If your document is large, especially if the first number is more than 1g, it is recommended that you save the first time as a PSB file, lest the PSD be saved for a long time and then be told that the store failed.

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