PhotoShop Layer Masks

Transcription

1 R O S E B R U F O R D C O L L E G E S O U N D & I M A G E D E S I G N N e w - M e d i a A u t h e r i n g U n i t PhotoShop Layer Masks B y R e z a Yo u n e s i May 2000 Semester 2b - Course Year 1 For Matt Ottewill

2 Contents Page 1 Page 2 Page 3 Page 10 Chapter 1 - Channels Chapter 2 - Layer Masks Chapter 3 - Demonstration Bibliography

3 Chapter 1 - Channels Page 1 Channels In order to understand masks and their functions it is important to have basic knowledge about channels and alpha channels. Channels: In PhotoShop images presents images through channels. An black & white is created by a greyscale channel, a RGB image created by three (Red, Green, Black) and a CMYK image created by four (Cyan, Magenta, Yellow, Black). Each of these channels is an 8-bit greyscale channel with 256 values and each channel contains data about the image. According to McClelland: To generate the colour image that you see on the screen, PhotoShop projects the greyscale data in each colour channel through a virtual colour lter. Alpha Channels: In PhotoShop selections can be saved as 8bit alpha channels, which can again be loaded into an image. Since PhotoShop presents an image in four or less channels any additional channel is handled as an alpha channel containing an individual greyscale image. An image can contain up to 24 channels when saved in TIFF or PhotoShop s native le format, however the le size increases with proportionally by increasing number of channels. GIF images are also able to contain one Alpha channel but the GIF format is restricted to 256 colours.

4 Chapter 1 - Layer Masks Page 2 Layer Masks Masks like Alpha channels are 8bit greyscale channels however masks cannot be saved unless converted to a selection or applied permanently to the image. Mask consists of black and white and by defaults the white areas present the visible selection area. Masks can be reshaped and resized by painting /black or white areas to the mask. Layer mask are available from both the layer and the channel palettes and masks are represented by a thumbnail in the layer palette when the speci c layer containing the mask is highlighted. Quick Mask Mode In the Quick Mask the unselected areas are projected through an semi-transparent mask which by default is red. The Mask can be reshaped by using the paint or erase tool. This feature gives the user the opportunity to see the rest of the image while editing in the selected part. The editing facilities in the Quick Mask mode are similar to Layer Masks., Quick Masks are temporary channels and are presented in italics in the Channel palette while working in Quick Mask mode.

5 Chapter 2 - Demonstration Page 3 Demonstration Masks allow advanced users to achieve signi cant results which might have appeared as impossible tasks with the basic PhotoShop tools such as the lasso tool. In order to accomplish better understanding about Layer Masks I will demonstrate some of their practical functions. The purpose of this demonstration is separate the main image from the background. Although the Lasso tool would be an alternative, masks are more suitable in order to create more precise selection.

6 Chapter 2 - Demonstration Page 4 The rst task is to select the colour channel, which presents the best natural contrast between the image and the background. By duplicating the colour channel a mask, containing greyscale data of the image, is created.

7 Chapter 2 - Demonstration Page 5 The High Pass lter exposes the edges and providing more simple and precise editing.

8 Chapter 2 - Demonstration Page 6 The Level tool boosts the contrast which might have been effected by the High Pass lter. However by boosting the contrast the edges set in the previous step might be affected and subsequently cause confusion while editing the mask.

9 Chapter 2 - Demonstration Page 7 By using the eraser tool and painting the shape of the selection is determined. White adds areas to the selection and use black to hide the unwanted areas. Close zooming is necessary to achieve more accurate editing by the edges.

10 Chapter 2 - Demonstration Page 8 Finally select the desirable/white areas by (Ctrl. + click) on the mask channel and return to the composite colour view (click on the RGB7CMYK channel in the channel palette).

11 Chapter 2 - Demonstration Page 9 Now the selection is available for further use and can be exported to other projects by using the basic Copy and Paste tools.

12 Page 10 Bibliography Books Weinmann E. Visual QuickStart Guide PhotoShop5 For Windows & Macintosh.Peachpit Press,1998 Essays & Articles McClelland D. The Great And Mysterious. Macworld Feb.1998