File size doesnt change when i convert image from 8 bit to 16 bit or vice versa in photoshop am i doing something wrong? Edit

[arex]

In photoshop i opened a 94KB jpeg image and went to image>mode and made sure the RGB colour and 8 bit/channel option is set. I then exported and saved it as a PNG file and the file size is 335kb.

Now i opened the original 94KB jpeg image again and went to image>mode and made sure its RGB colour and 16 bit/channel option is set. I then exported and saved it as a PNG file and the file size is STILL 335kb.

shoudnt the image file size suppose to increase when you increase the colour depth in your image?. Im using the latest adobe photoshop. Im a beginner in photoshop and I dont understand why the file size is still the same. How do i resolve this issue.

 

[USAFRet]

Increasing the color depth does not automagically add new information in the image.

 

[rgd1101]

only if the original image use more then 8 bit color

 

[arex]

When i open the original image it says RGB 8 colour and 8 bit/channel option and when i converted it to 16 bit, the file size dont change. Am i doing something wrong because i have to do this for my college assignment and explain what colour depth is and how it affects file size.

 

[USAFRet]

When i open the original image it says RGB 8 colour and 8 bit/channel option and when i converted it to 16 bit, the file size dont change. Am i doing something wrong because i have to do this for my college assignment and explain what colour depth is and how it affects file size.

Its starting out at 8 bit/channel.
You can't add new information to the image by changing that to 16bit/channel.

For your assignment, go the other way.
Start out with a 16bit/channel image, then reduce it.

 

[arex]

how do i start the other way round? im a noob in Photoshop i only been using it for a month.

 

[USAFRet]

how do i start the other way round? im a noob in Photoshop i only been using it for a month.

Where is your image coming from?

 

[arex]

i downloaded the image from google image and in Photoshop i click file>open and then select the image from my hard drive. It opens the image as 8 bit channel as default.

 

[USAFRet]

i downloaded the image from google image and in Photoshop i click file>open and then select the image from my hard drive. It opens the image as 8 bit channel as default.

Well, that's your issue.
You're starting from the wrong image.

This is a Photoshop class? Digital graphics, or photography?
You need a better source image.

 

[arex]

ok where do i get better source image?

 

[USAFRet]

ok where do i get better source image and yes Im doing unit 30 digital graphics in BTEC LEVEL 3 IT course, its for my M2 and D2 criteria for my coursework.

Seeing as you have Photoshop...you can make one...

 

[arex]

ok so i kinda understand now, you cant really change the colour depth of an image to 16 bit if its already 8 bit colour depth image.

 

[rhysiam]

Also, I don't believe regular JPEG support 16 bits per channel (=48bit per pixel). SO, all JPEG source images will - by a file type limitation - be 8bit colour depth. Then, even if you start with a proper 16bit image and save it as a JPEG, it will get converted down to 8bit. There are extended types of JPEGs which don't have this limitation, but will require image viewers with support for them.

 

[USAFRet]

Also, I don't believe regular JPEG support 16 bits per channel (=48bit per pixel). SO, all JPEG source images will - by a file type limitation - be 8bit colour depth. Then, even if you start with a proper 16bit image and save it as a JPEG, it will get converted down to 8bit. There are extended types of JPEGs which don't have this limitation, but will require image viewers with support for them.

This is true.