I studied about a bit map at yesterday.
I understood a algorithm about the bitmap.
See code and explanation below.

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//This method is invoked when choose button clicked
- (void)imagePickerController:(UIImagePickerController*)picker
didFinishPickingImage:(UIImage*)image
editingInfo:(NSDictionary*)editingInfo
{
//Restore the buttons
statusButton.hidden = NO;
colorButton.hidden = NO;
fillColorButton.hidden = NO;
doneButton.hidden = NO;
allClearButton.hidden = NO;
layer1ClearButton.hidden = NO;
layer2ClearButton.hidden = NO;
layer3ClearButton.hidden = NO;
saveButton.hidden = NO;
loadButton.hidden = NO;

//Hide an ImagePickerView
[self dismissModalViewControllerAnimated:YES];

//Create a new UIImage object(originalImage) and substitude originalImage for choose Image.
UIImage* originalImage;
originalImage = [editingInfo objectForKey:UIImagePickerControllerOriginalImage];

//Create a new CGSize object(size) and initize it.it size is full screen size.
CGSize size = { 320, 480 };
//Creates a bitmap-based graphics context and makes it the current context.
UIGraphicsBeginImageContext(size);

//create a CGRect object for use drawInRect
CGRect rect;
rect.origin = CGPointZero;//(0, 0)
rect.size = size;
[originalImage drawInRect:rect];

//Get an image by use UIGraphicsGetImageFromCurrentImageContext method. //this method is Returns an image based on the contents of the current bitmap-based graphics context.
shrinkedImage = UIGraphicsGetImageFromCurrentImageContext();

//Removes the current bitmap-based graphics context from the top of the stack.
UIGraphicsEndImageContext();



//create the CGIMageRef(cgImage) object and institute cgImage for shrinkedImage.CGImage. //CGImage is UIImage class property. CGImageRef cgImage;
cgImage = shrinkedImage.CGImage;

// get an information about image //__SIZE_TYPE__ is macro and iqual to unsigned int //typedef __SIZE_TYPE__ __darwin_size_t; /* sizeof() */ //typedef __darwin_size_t size_t; unsigned int width;//320
size_t height;//480
size_t bitsPerComponent;//8
size_t bitsPerPixel;//32
size_t bytesPerRow;//1280 = 4byte*320
CGColorSpaceRef colorSpace;
CGBitmapInfo bitmapInfo;//8193
bool shouldInterpolate;//true
CGColorRenderingIntent intent;//14081600

width = CGImageGetWidth(cgImage);
height = CGImageGetHeight(cgImage);
bitsPerComponent = CGImageGetBitsPerComponent(cgImage);
bitsPerPixel = CGImageGetBitsPerPixel(cgImage);
bytesPerRow = CGImageGetBytesPerRow(cgImage);
colorSpace = CGImageGetColorSpace(cgImage);
bitmapInfo = CGImageGetBitmapInfo(cgImage);
shouldInterpolate = CGImageGetShouldInterpolate(cgImage);//Returns the interpolation setting for a bitmap image.
intent = CGImageGetRenderingIntent(cgImage);//Returns the rendering intent setting for a bitmap image.
/*kCGRenderingIntentDefault, kCGRenderingIntentAbsoluteColorimetric, kCGRenderingIntentRelativeColorimetric, kCGRenderingIntentPerceptual, kCGRenderingIntentSaturation*/
// Create a dataProvider object and get a data provider
CGDataProviderRef dataProvider;// which you use to move data into and out of Quartz. // CGDataProviderRef allow you to supply Quartz functions with data.
dataProvider = CGImageGetDataProvider(cgImage);//Returns the data provider for a bitmap image.




//get an information about bit map datas
CFDataRef data;
data = CGDataProviderCopyData(dataProvider);//data = 614400byte = 153600(320*480)*4 //Returns a copy of the provider’s data.

//A reference to an immutable CFData object.
UInt8* buffer;//buffer is a pointer to UItnt8 //typedef unsigned char UInt8;

buffer = (UInt8*)CFDataGetBytePtr(data);
//Returns a read-only pointer to the bytes of a CFData object.

// give the effect of change color per pixel
NSUInteger i, j;
for (j = 0; j < i =" 0;" style="font-weight: bold; font-style: italic; color: rgb(255, 0, 0);"> // get the pointer information /*address space↓↓↓// //___________// //１pixel// //___________// //blue // //___________// //green // //___________// //red // //___________// //next pixel // //___________// //blue // //. // //. // //. */
UInt8* tmp;
tmp = buffer + j * bytesPerRow + i * 4;
//tmpはbufferのメモリ空間を頭から４バイトずつ移動しながらピクセルに効果を与えている。
// RGBの値を取得する
UInt8 r, g, b;
r = *(tmp + 3);//r
g = *(tmp + 2);//g
b = *(tmp + 1);//b

// 輝度値を計算する
UInt8 y;
y = (77 * r + 28 * g + 151 * b) / 256;//重み付きの平均値 /* この重み付きの平均値 gray は輝度と呼ばれるもので、カラーテレビの信号処理 に使われます。輝度は色の明るさを表します。 　重みを付けて平均を取るのは、人の視覚は赤・緑・青に対してそれぞれ感度が異 なるためで、 　　　　青 < 赤 < 緑 の順に感度が高くなります。最も感度の高い色に重みを持たせています。 http://www.asahi-net.or.jp/~uc3k-ymd/Glib32/loadbmp.html*/ // 輝度の値をRGB値として設定する /*********ネガポジ************ *(tmp + 1) = 255-b;//b *(tmp + 2) = 255-g;//g *(tmp + 3) = 255-r;//r ***************************/

*(tmp + 3) = 0;//r
*(tmp + 2) = g;//g
*(tmp + 1) = 0;//b

}
}

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I could get the pixel data of image and various effect to image.
for example gray scale nega


I couldn't understand some a method.((UInt8*)CFDataGetBytePtr(data);)
I'll understand it.