ch1:android digital imaging:formats concepts and optimization

android digital image formats:lossless versus lossy

1. GIF is not recommended in androd os , cause is lossless , it doesn‘t not away image data to achieve better compression results.
2. JEPG is lossy digial image file format. it will thorws away image data in order ot achieve smaller file sizes .  and is unrecoverable after compression . so please make sure to save an orginal uncopressed image file
3. the most recommended format is PNG , because it‘s lossless andd has both high image quality and reasonable level of compression efficiency .
4. andoid also support webp image format.

the foundation of digital iamges:pixels and aspect ratio

1. to found out the number of pixels and image , simplely multiply the width pixels by height pixels .
2. aspec ratio will define how square or rectangular an image or display screen is.

The color of digital imagel: color theory and color depth

1. Color values for iamge pixels are defined by the amount of there different colors : red , green ,and blue .
2. the number of bits used to repersent coloer in a igital image is referred to as the color depth f that image.
3. the lowest color depth exists in an 8-bit indexed color image , which has 256 clolr value . it used for GIF and PNG8 formats . the medium color depth image features a 16-bit color depth which contains 65536 colors . but it‘s not supported by android os . a high color depth iamge features a 24-bit color . include JPEG, PNG,TIFF and webP.
4. using 24-bit color depth will give you the hightset quality level. Since it‘s lossless , it has the highest quality compression .

Representing colors in Androd:Hexadecimal Notation

1. it‘s also important to note that in andoid .color is not only used in 2D digital iamgery . also called itmap imagery .
2. #FFFFFF represents a color of whit . As each slot in this 24-bit hexadecimal representation represents on base 16 value . to get 256 for each RGB color will take 2 slots .
3. it‘s important to note that there is also a 32-bits image color depth whose data  values are represented using an ARGB . whre the A stand for alpha . which is short for alpha channel . 
   the alpha stand for transparency 。

Image Compositing : Alpha channels and Blending Modes

1. Blending modes are implemented in Android using the PorterDuff class.
2. Some of Android’s PorterDuff blending modes include ADD, SCREEN, OVERLAY, DARKEN, XOR, LIGHTEN, and MULTIPLY.

Digital Image Masking: A Popular Use for Alpha Channels

1. one of the primary applications for alpha channels is to mask out areas of an image for compositing .
2. Masking is the process of cutting subject matter out of an image and placing it onto its own layer using an alpha channel.
3. You can’t really do effective image compositing without doing masking first, so it’s an important area for graphics designers to master.
4. masking can be done by using selection tools and sharpening and blur algorithms