Reactive Imaging

There is an art to working with very large Photoshop images. You can't just open a large canvas and begin adding dozens of layers until you run out of memory. Strategies are involved. When large files are common, the strategy begins with system configuration. If is an unusual occurrence, temporary adjustments to work behavior will have to suffice.

1. Only necessary applications | before launching PS, disable all unnecessary apps (iTunes, Safari, etc.); it is too late to do so after PS has begun swapping to scratch disk; restarting your computer is the only reliable way to regain available RAM and disable disk swapping
2. Adjust PS preferences | assign more memory; reduce history states and cache levels; assign external fast scratch disk with contiguous free memory; remember you must restart PS to effect changes
3. Resolution | specify ideal resolution with consideration for all future output; offset printing is typically 250-300 ppi; digital posters often range 100-240 ppi at final output size (>200 ppi for Giclée, high resolution prints on smooth paper)
4. RGB color space | pros: RGB increases available filters and reduces channels (=smaller file size) | cons: large areas of rich black conversions for CMYK printing can be a bit tricky (>300% total ink)
5. TIFF (LZW) | TIFF supports layers, RGB and CMYK; includes options for smaller files than PSD through lossless LZW compression
6. PSB | for super large files, PS includes to ability to save documents in the "large document format"
7. One pixel document | PS saves multiple copies of the file for undos, history, etc. Often overlooked is the clipboard which can get quite large when something is copied. Keep a separate document window open that is 1x1 pixel with the entire area selected (marching ants). Periodically click the window and Copy (cmd-c) to significantly reduce the size of the clipboard.
8. Layer management | several layers may be required for a particular effect; once that is achieved, save the document, open a copy and combine the layers; rarely should every layer for each effect be required throughout development of entire project; global adjustment layers can be added after the main composition is flattened; if you need something from earlier, reopen the prior version, make edits, combine the layer again (shift-opt-cmd-E) and shift-drag it back into the working document
9. Alpha channel management | where possible use vector paths instead of alpha channels and use alpha channels instead of layers