A bit late to this, but I was having the same issues but I did find a fix to it. I have only tested this through one image so far but it seemed to work.
I converted them into JPG-JPEG using XnConvert (I am not advertising this product, it is just the one that worked for me). With the Format settings (in the Format section) as shown in the attached image. Preserve the Extension and the Metadata whilst maxing the quality and setting the DCT to "Float (Best but Slowest)". This worked for me and I hope it will work for you as well should you not have found an answer by now.
Help Sought: Pixelated images on digital picture frame
in Photo & Camera Discussions
Posted
A bit late to this, but I was having the same issues but I did find a fix to it. I have only tested this through one image so far but it seemed to work.
I converted them into JPG-JPEG using XnConvert (I am not advertising this product, it is just the one that worked for me). With the Format settings (in the Format section) as shown in the attached image. Preserve the Extension and the Metadata whilst maxing the quality and setting the DCT to "Float (Best but Slowest)". This worked for me and I hope it will work for you as well should you not have found an answer by now.