Reducing image dimension increases image size - why ?

[Painterman]

Hi

 

I'm sorry if the topic title doesn't leaves the correct impression on what my problem is.

 

I have a .jpeg image which originally had the dimensions 5184 x 3456 and the size was 522kb

 

I have cropped the image and its dimensions is now 2009 x 2997 and saved it as a jpeg again - in the Save Configuration dialog I choose the quality to be 100.

 

The end result is that I now got an image which has the size of 2.07mb !

 

Why did the image size increase 4 times ?

 

What did I do wrong ?

 

 

 

 

[Ishi]

I am rather puzzled why a very huge image with 5184 x 3456 dimensions would have only 522KB file size in the first place when it normally should have 3MBs or more. Are you sure you have checked the properties of the correct file? This might be possible if the image has poor details anyway and lots of pixels with just the same hue. I have scratchy ideas of how this came to be and those are theoretical.

 

If you save a .jpg with 100% quality, the file size tends to go up. I have seen this happen on another image editing program called Photoscape as well.

Edited December 4, 2014 by Ishi

[midora]

What did I do wrong ?

 

You are expecting that the original image has been saved with a quality of 100.

 

Less quality means smaller file size in the case of jpeg.

 

Check the "File size:" info In the save configuration dialog above the preview.

If you are changing the quality slider then you will see the final file size there.

 

And respect the image size in RAM is 70 MB. (5184 x 3456 x 4).

[Painterman]

I am rather puzzled why a very huge image with 5184 x 3456 dimensions would have only 522KB file size in the first place when it normally should have 3MBs or more. Are you sure you have checked the properties of the correct file? This might be possible if the image has poor details anyway and lots of pixels with just the same hue. I have scratchy ideas of how this came to be and those are theoretical.

 

If you save a .jpg with 100% quality, the file size tends to go up. I have seen this happen on another image editing program called Photoscape as well.

 

 

Hi

 

I'm sorry for not providing some rather crucial information in my initial post !

 

The image originally was a 13mb CR2 file (Canon Raw) which I converted in photoshop - after the conversion I ended up with to the 522kb .jpeg file

 

Alle the images are portraits and the background was black-ish in color, so I'll guess this is the reason why photoshop were able to compress the image down to that size.

 

I still have access to the .jpeg files and also photoshop, now is the question if I should try and chop the images and save them afterwards using photoshop instead of using pdn ?

[Pratyush]

That happens because .JPEG is lossy format. It would have about same size if the image was saved in lossless image format like .PNG.
JPEG is lossy compression format which gain smaller size on the cost of image quality. It happens that the lesser the size of the image, more the loss of quality in image. While compressing, some of the details of image are chopped off and what appears in its place is called as JPEG noise. So, whenever you save the older JPEG image in new 100% format, It hardcodes the old JPEG noise into new JPEG. It should be decent trade off of around 75-80 % image quality for during saving.
 
Just try saving with some good level of image quality appropriate for you not the 100%

Edited December 4, 2014 by Pratyush