Is there anyway to reduce the Image file size or Raw RGB buffer ?
Actually I have RGB buffer which it has 500KB with 320X420 size.I tried to save it to disk using UIimage and it comes to 240 KB.
As per the image size, I want it to have less than 50KB or so.(loosing quality is OK)
Is it possible ?
Thanks,
Raghu
See Trevor Harmon's excellent post on the subject.
The 240KB size sounds exactly like the raw RGB image data, uncompressed (320x420x3). Doesn't the iPhone have a PNG or JPEG exporter? The internet says to use UIImageJPEGRepresentation or UIImagePNGRepresentation and NSData writeToFile.
Related
I have an image captured via webcam of my cat (the subject might not be important). I've aquired it as a 31 kB JPG file. When I open it with an image editor, then save it (without alteration) as a PNG (max. compression) it stores as a 297 kB file.
Why is the PNG file 10x larger than the original JPG. As I understand it, opening a JPG is lossless, and saving a PNG is lossless. So, where does all the extra data come from? If the image comes entirely out of the small file, why does it then re-save to 10x the size on disc?
Please read this carefully. I'm not asking why the two formats produce different file sizes from an original image. I'm asking why opening an existing JPG then saving that exact same image as PNG is 10x bigger. I don't think that this is a duplicate question as far as I can ascertain.
Some tests I've done:-
I've looked at both JPG and PNG and they look identical.
I've zipped both files and got cat.jpg.zip as 31 kB, and cat.png.zip as 296 kB. I take this to mean that both files are fully compressed with virtually no latent redundancy.
I've tried this via the BMP format as well; cat.jpg (31 kB) -> cat.bmp (922 kB) -> cat.bmp.zip (404 kB).
Any ideas regarding the mysterious extra data..?
JPEG inherently produces better compression than PNG. However, JPEG trades off fidelity to the original image for better compression. PNG reproduces the original exactly.
If you go from JPEG to PNG, you are not going to see a changes.
If you go from PNG to JPEG, it is likely you ill see a lot of change.
JPEG uses a series of compression techniques. One of them, the DCT, transforms the image. This creates a subtle waviness in color. For example, if you start with a solid red block that is all one color, JPEG produces a lot of slight color variations.
PNG compression relies on finding repeated pixel patterns in scan lines. The subtle color variations introduced by JPEG can make PNG compression less effective.
The extra data you refer to is simply the difference in how the two format represent the same image.
If I take a JPEG image from a camera and convert to PNG, the result is usually about 10 times larger.
For a PNG Graphic image going to JPEG, I normally get files about 1/3 smaller.
JPG uses lossy compression, while PNG uses loseless compression. When you convert JPG to PNG, what actually happens is uncompressing from JPG and saving the results in PNG.
The "extra data" is actually due to different algorithms used.
As for why zipped files also have different size, that's because PNG has to save all pixels(including those JPG has lossy compressed) loselessy.
Is it possible convert anNSData *dataImage witch was a format jpeg or png and convert it to PNG interlaced? i know about compression image UIImagePNGRepresentation but i think it convert just to non-interlaced PNG. So, how should i set option for an UIImage or NSData to interlaced PNG?
UIImagePNGRepresentation makes only non-interlaced png.
Nice question, but i think it is impossible using UIKit.
I think you should use libpng to create interlaced png.
Look at this article , there you can find Minimal Example of writing a PNG File
When you set png header in this method
png_set_IHDR(png_ptr, info_ptr, width, height,
bit_depth, color_type, PNG_INTERLACE_NONE,
PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
try to change PNG_INTERLACE_NONE to PNG_INTERLACE_ADAM7_PASSES
The Picture taken from the iphone cam is nearly 2.5 Mb, How to reduce this size ,I have tried
UIJPEGRepresentation(image,0.1f),but it does not effect the size ?
You really can't reduce the size the images takes up in memory.
When an image is loaded, basically a UIImage object the size wil be width x height x 4 bytes. That is the size the an uncompressed image will take up in memory.
Since you can use compressed images all image, once loaded in a UIImage will be uncompressed.
If you really need so save some memory, save the image to disk and create a thumbnail which you use in your app. Then when need you can load the larger image and use it,
Try using the Resize method in UIImage+Resize.h
https://github.com/AliSoftware/UIImage-Resize
[aImgView setImage:[ImageObjectFromPicker resizedImageWithContentMode:UIViewContentModeScaleAspectFit bounds:YourSize interpolationQuality:kCGInterpolationHigh]];
Currently I am dealing with the problem that I have pdf file with lots of 1024x768 images in it and am trying to optimize the pdf's file size, but the only solution that I thought is good enough for now is compressing the images with jpeg compression. The problem is that I did not find any way to do that with iOS APIs. Am I missing something, is there a way?
I`m welcome to suggestions on how to optimize the pdf with other means (lowering the resolution of the images is not a good solution for me).
Edit: If someone knows another API to use for pdf generation on iOS - links would be much appreciated.
Thanks in advance.
Actually you can use a UIImageJPEGRepresentation. But there's another step, to then use a JPEG data provider to draw the image:
NSData *jpegData = UIImageJPEGRepresentation(sourceImage, 0.75);
CGDataProviderRef dp = CGDataProviderCreateWithCFData((__bridge CFDataRef)jpegData);
CGImageRef cgImage = CGImageCreateWithJPEGDataProvider(dp, NULL, true, kCGRenderingIntentDefault);
[[UIImage imageWithCGImage:cgImage] drawInRect:drawRect];
This worked well for me when drawing to a PDF context. 0.75 compression quality reduced the size of my image-laden PDF by about 75% and it still looked fine.
If anyone is interested I found a solution to my problem by using a free pdf library - libHaru. It gave me the needed functionality to add a JPEG compressed image to the generated pdf file.
If you'd like to compress images you can use UIImageJPEGRepresentation
NSData * UIImageJPEGRepresentation (
UIImage *image,
CGFloat compressionQuality
);
you could jpeg convert/compress a PNG image with
NSData *someImageData = UIImageJPEGRepresentation(pngImage, 0.6); // quality 0.6 (60%) (from 0.0-1.0).
UIImage *newCompressedJPG = [UIImage imageWithData:someImageData];
But i don't think so this will reduce your PDF size. Because when you place the UIImage to your pdf the RAW image get's placed (as far as i know).
Update 1:
its compressibility varies from 0.0 to 1.0 (thanks to Leena)
I have a matlab code and it generates a .png image of 1024*768 resolution. The images are about 450KB in size and I need to know how to optimise and compress these images using matlab.
Can't I play with the quality as in JPEG ?
I read the imwrite manual and don`t seem to find a good way to do this.
Is there any way to achieve it in matlab ?
By design PNG files are lossless - there is no 'quality' to be adjusted (it's probably why a mod changed your question title).
You can reduce the number of colors in the image (the color depth) which will in turn reduce filesize (PNG-8 instead of PNG-24, for example), but the whole point of PNG is it produces lossless images, so there is simple no quality value a la JPEG.
Taken from the manual :
A parameter of input in case it is JPEG:
'Quality' - A number between 0 and 100; higher numbers mean higher quality (less image degradation due to compression), but the resulting file size is larger.
imwrite(x,'c:\1.jpg','Quality',10)
edit: Sorry, I answered this one while the title was JPEG and not PNG.
PNG doesn't support any quality settings - it is a lossless format. The compression it applies is generally as good as possible.