why has my received image's size increased after transfer?

For my project, i am testing MMS behavior of different file format of different dimension. before sending the MMS, it converts my msg to MMS, converting PNG images to JPG file. Here only the file size reduces drastically because the dimension has reduced. Till now its good.

Now when I send the now JPG image via MMS, if my file sent was 31.2KB, when received it becomes 31.3KB and in some situation the increase is bigger. This happen only with PNG file which upon transmission change the PNG to JPG before sending and thus I receive a bigger (in KB) JPG image. All other format (BMP, JPG, GIF) remain same or decrease in size (KB). I did the same test series more than 10 times and the change is consistent, same change always. It happen with big dimension image only (>500KB) as smaller ones remain PNG format when send and received.

BMP Original Image: bmp_810KB.bmp - 576x480 - 810KB --Sent Image: bmp_810KB.jpg - 288x240 - 8.94KB --Received Image: bmp_810KB.jpg - 288x240 - 8.78KB

JPG Original Image: jpg_810KB.jpg - 1024x957 - 810KB --Sent Image: jpg_810KB.jpg - 514x480 - 34.9KB --Received Image: jpg_810KB.jpg - 514x480 - 28KB

PNG Original Image: png_810KB.png - 700x525 - 810KB --Sent Image: png_810KB.jpg - 640x480 - 55KB --Received Image: png_810KB.jpg - 640x480 - 55.9KB

I have tried to check RGB percentage change, HSV changes, MSE but I cannot get a proper pattern that can explain this increase in size. Is it redundant data? I have no idea how to calculate that on matlab?

If someone has an idea about what can be changing to cause the increase please do help me out.

Thanks, S

Answer 1

[Walter Roberson]

What kind of system are you sending from, and what kind of system are you sending to?

Is it possible that the sending system measures size in "kilobytes" (1024 bytes per kilobyte) and that the receiving system measures size in "kibibytes" (1000 bytes per kilobyte) ?

[Sweta]

If this was the case then for my other test of other formats it should have been same. I do not think it is the system as I used identical set of mobile and the same carrier network for sending and receiving. Even sending the image to the same number gave me the same results; that is I sent the image to my number (sending and receiving on same mobile).

What is strange is that when I sent JPG image, I received a smaller image in size(kb). The increase is happening only with PNG file. When the image is attached to the message, it is converted to MMS.. in this conversion process the PNG image becomes JPG. Only in this case that the image is bigger in size when received.

If not saturation, what else can influence size of an image for it to increase? How can I test it to prove that this given factor is in fact causing the increase... :s

Thank you for your help.

[Walter Roberson]

Wait... why is MMS converting image file formats? Is MMS defined to only be able to encapsulate JPG files? I would have thought that MMS would be able to encapsulate arbitrary binary files, using something similar to MIME ?

[Sweta]

Well for small images there is no conversion, but large images of format BMP or PNG do undergo some conversion so that the image is suitable for MMS (mobile has some limitation as well as the network). In this cropping and resizing process, the image no longer remains in its format, it becomes JPG. I think it depends on the mobile set, which compression or conversion techniques it use.

[Walter Roberson]

It is not impossible that on some images, the (lossless) compression of PNG does better than the compression used in the JPG file (with unknown settings.) In particular, lossless JPG or JPG with 100% "quality" both produce large files.

Looking around I see that the receiving message store (closest to the target system) is responsible for doing any compatibility conversion, and that the conversion is according to that message store's guess of what the capabilities of the receiving system are.

I would suggest using imfinfo() or similar to examine the JPG images to see if it can be determined what compression parameters were used. You might need to examine the EXIF headers.

[Sweta]

I tried imfinfo() but the information is very limited and looks same for sent and received image.

>> info = imfinfo('png_2000KB_s.jpg')

info =

           Filename: 'C:\Program Files\MATLAB\R2012a\Mine_Test\png_2000KB_s.jpg'
        FileModDate: '03-Jul-2013 19:12:24'
           FileSize: 65134
             Format: 'jpg'
      FormatVersion: ''
              Width: 640
             Height: 480
           BitDepth: 24
          ColorType: 'truecolor'
    FormatSignature: ''
    NumberOfSamples: 3
       CodingMethod: 'Huffman'
      CodingProcess: 'Sequential'
            Comment: {}

>> info = imfinfo('png_2000KB_r.jpg')

info =

           Filename: 'C:\Program Files\MATLAB\R2012a\Mine_Test\png_2000KB_r.jpg'
        FileModDate: '02-Jul-2013 19:17:28'
           FileSize: 66043
             Format: 'jpg'
      FormatVersion: ''
              Width: 640
             Height: 480
           BitDepth: 24
          ColorType: 'truecolor'
    FormatSignature: ''
    NumberOfSamples: 3
       CodingMethod: 'Huffman'
      CodingProcess: 'Sequential'
            Comment: {}

I am using MATLAB2012 and to get info about EXIF I have to install ExifTool. I will try your suggestion and check the Exif info to see if there are some differences in there.

Thanks for your suggestion. Will keep you posted :) Thanks

[Walter Roberson]

Huffman / Sequential is JPEG's lossless compression algorithm. It is not as efficient as the DEFLATE algorithm used for PNG files, because of the preprocessing that PNG uses to reduce the complexity of the bitstream, and the improvements that dynamic huffman (DEFLATE) can have over static huffman (JPEG)

[Sweta]

I tried to extract the EXIF info and I find only one similarity in all my files which have increased in size.. the JFIFVersion! For my sent files it is JFIFVersion 1.01, but my received files are JFIFVersion 1.02.

FileName : png_1799KB_s.jpg ------------------------------ FileName : png_1799KB_r.jpg

FileSize : 41 kB ---------------------------------------------------- FileSize : 42 kB

FileType : JPEG --------------------------------------------------- FileType : JPEG

MIMEType : image/jpeg ----------------------------------------- MIMEType : image/jpeg

JFIFVersion : 1.01 ------------------------------------------------ JFIFVersion : 1.02

EncodingProcess : Baseline DCT, Huffman coding ---- EncodingProcess : Baseline DCT, Huffman coding

YCbCrSubSampling : YCbCr4:2:0 (2 2) --------------------- YCbCrSubSampling : YCbCr4:2:0 (2 2)

ImageSize : 582x480 ---------------------------------------------- ImageSize : 582x480

Can this change in format (and all other info remaining same) be a reason for a slight change in size? Some which were 1.01, changed to 1.02 but has a change in YCbCrSubSampling from YCbCr4:2:0 to YCbCr4:2:0 (2 2). Those were the JPEG files which decrease in size.

Only PNG from origin converted to 1.01 first and changed to 1.02 upon received but all other info are same. Apparently JFIF 1.02 stores more info? However, I did not find yet a reliable source online that states that JFIF 1.02 did influence file size. According to you, can this explain the slight increase in size? If yes, how to prove this?

Thank you very much for your help.