# Uncertainty in Visual Generative AI
## 2 Background
### Image Retrieval and Visual GAI
#### 2.1.2 Text-to-Image Generation  
As pointed out in Table 2, there are several popular text-to-image diffusion models, which rapidly rose in popularity due to their accessibility and ease of use in 2021. Unlike popular generative adversarial networks (GANs) that consist of two neural networks (a discriminator and a generator) that are trained to create new images, a diffusion model adds or removes Gaussian noise to an image depending on the task [50; 80]. OpenAI began the craze with its release of DALL-E in February 2021 [29]. DALL-E is a fine-tuned version of GPT-3 specifically for text-to-image generation through an autoregressive transformer architecture called the discrete variational autoencoder (dVAE) [29; 30]. In response to this, an independent group of researchers introduced a smaller, open-source model originally called DALL-E Mini, but now known as Craiyon [36; 37]. As opposed to DALL-E, Craiyon leverages a bidirectional encoder and pre-trained models to translate a textual prompt to an image [36]. Craiyon is a freemium service for which a free \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Model** & **Open-Source** & **Cost Structure** & **Tier/Image/Version** & **Cost** \\ \hline \multirow{3}{*}{DALL-E 2} & \multirow{3}{*}{No} & \multirow{3}{*}{Pay-per-image} & 1024 \(\times\) 1024 & 0.02 USD/image \\  & & & 512 \(\times\) 512 & 0.018 USD/image \\  & & & 256 \(\times\) 256 & 0.016 USD/image \\ \hline \multirow{3}{*}{\begin{tabular}{c} DALL-E 3 \\ (Quality: HD) \\ \end{tabular} } & \multirow{3}{*}{No} & \multirow{3}{*}{Pay-per-image} & 1024 \(\times\) 1792 & 0.12 USD/image \\  & & & 1792 \(\times\) 1024 & 0.12 USD/image \\  & & & 1024 \(\times\) 1024 & 0.08 USD/image \\ \hline \multirow{3}{*}{\begin{tabular}{c} DALL-E 3 \\ (Quality: Standard) \\ \end{tabular} } & \multirow{3}{*}{No} & \multirow{3}{*}{Pay-per-image} & 1024 \(\times\) 1792 & 0.08 USD/image \\  & & & 1792 \(\times\) 1024 & 0.08 USD/image \\ \hline \multirow{3}{*}{\begin{tabular}{c} Craiyon \\ \end{tabular} } & \multirow{3}{*}{Yes} & \multirow{3}{*}{\begin{tabular}{c} Free; \\ Subscription \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} Free \\ Subscript \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} N/A \\ 6 USD/mo or 60 USD/yr \\ Professional \\ \end{tabular} } \\  & & & & 24 USD/mo or 240 USD/yr \\ \hline \multirow{3}{*}{\begin{tabular}{c} Stable Diffusion 1 \\ \end{tabular} } & \multirow{3}{*}{Yes} & \multirow{3}{*}{\begin{tabular}{c} Free; \\ Pay-per-image \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} Free \\ Stable Diffusion XL 1.0 \\ \end{tabular} } & \multirow{3}{*}{\begin{tabular}{c} N/A \\ 0.016 USD/image \\ Stable Diffusion XL 0.9 \\ \end{tabular} } \\  & & & & 0.005 USD/image \\  & & & & 342 \\  & & & & 342 \\  & & & & 342 \\ \hline \multirow{3}{*}{\begin{tabular}{c} Midjourney \\ \end{tabular} } & \multirow{3}{*}{No} & \multirow{3}{*}{Subscription} & \multirow{3}{*}{\
\begin{tabular}{c} Basic \\ Standard \\ Pro \\ \end{tabular} } & \multirow{3}{*}{
\begin{tabular}{c} 10 USD/mo or 96 USD/yr \\ Standard \\ Pro \\ \end{tabular} } \\  & & & & 342 \\  & & & & 342 \\ \hline \hline \end{tabular}  
* Cost depends on the number of denoising steps; the default number of 30 was used to estimate cost per image offered through Stability AI. 2 Regular Stable Diffusion models’ cost depends on height and width; the default value of 512 \(\times\) 512 was used to estimate cost per image.  
\end{table} 
Table 2: Comparison of text-to-image models (as of September 2023). version exists for public use; however, a subscription plan can be purchased to remove the Craiyon logo and decrease generation time [35]. DALL-E 2 improves upon its earlier version by leveraging Contrastive Language-Image Pre-training (CLIP) embeddings before the diffusion step of the model [31; 32]. In 2022, Google announced two models. First, they revealed Imagen, which is another diffusion model [30], but they later revealed a sequence-to-sequence model called Pathways AutoRegressive Text-to-Image Model (Parti) [42].